SUCCESS! In Clinical Laboratory Bacteriology Aerobic G-N

A fermentative gram-negative bacillus that is oxidase positive, motile, and grows well on MacConkey agar is A. Aeromonas hydrophila B. Pseudomonas aeruginosa C. Stenotrophomonas maltophilia D. Yersinia enterocolitica

A. Aeromonas hydrophila is typically found in fresh water and has been implicated in human infections. Growth on MacConkey agar and a positive oxidase reaction are characterisic of this organism. A positive oxidase reaction differentiates this organism from all of the Enterobacteriaceae, except the recently added Plesiomonas shigelloides. On sheep blood agar, many strains of Aeromonas produce beta-hemolysis.

The causative agent of the septicemic, hemolytic disease known as Oroya fever is A. Bartonella bacilliformis B. Burkholderia mallei C. Haemophilus aegyptius D. Yersinia pestis

A. Bartonella bacilliformis is the causative agent of Oroya fever and verruga peruana. It is a pleomorphic, gram-negative rod that is an intracellular parasite of red blood cells and can be cultured from blood in the acute stage of the disease. The disease is rare and occurs primarily in South America

Which of the following is an ocasional cause of respiratory tract infections and is rapidly urea positive? A. Bordetella bronchiseptica B. Brucella abortus C. Campylobacterfetus D. Escherichia coli

A. Bordetella bronchiseptica in humans produces either a respiratory illness or wound infections. The organism is a part of the normal respiratory flora of laboratory animals such as rabbits and guinea pigs. B. bronchiseptica may cause problems for researchers because it can cause outbreaks of bronchopneumonia in experimental animals. It also causes kennel cough in cannines.

The porphyrin test is most useful for the identification of which of the following? A. Campylobacter B. Haemophilus C. Moraxella D. Neisseria

B. Strains of Haemophilus able to synthesize heme are identified by the porphyrin test. Species such as H. influenzae, which require heme, would give a negative test result, whereas H. parainfluenzae would be positive. A red color is indicative of a positive reaction in this test

The porphyrin test determines an organism's requirement for A. Cystiene B. Hemin C. NAD D. Thiol

B. The porphyrin test is commonly used to test for the X factor (hemin) requirement of Haemophilus spp. A positive test result indicates that the organism possesses the enzymes to convert aminolevulinic acid (ALA) into porphyrins and, therefore, would not require hemin. If porphyrins are produced, this rapid test will show red fluorescence under UV light after a 4-hour incubation period.

Which of the following organisms produce a positive phenylalanine deaminase reaction? A. Citrobacterfreundii B. Klebsiella pneumoniae C. Providendia stuartii D. Yersinia enterocolitica

C. Members of the tribe Proteae are characteristically positive for phenylalanine deaminase (PDA). This includes Proteus vulgaris, Providencia stuartii, and Morganella morganii. Tatuella ptyseos belongs to the family Enterobacteriaceae and is also PDA positive.

The characteristics of being lactose negative, citrate negative, urease negative, lysine decarboxylase negative, and nonmotile best describe which organism? A. Proteus vulgaris B. Yersinia pestis C. Salmonella enterica D. Shigella dysenteriae

D. Shigella dysenteriae D. Shigella dysenteriae, the type species of the genus, is a causative agent of bacillary dysentery. Differential and selective media for the recovery of enteric pathogens from stool samples would demonstrate Shigella species as H2S negative, non-lactose-fermenting, gram-negative bacilli. Further biochemical testing would generally show these organisms to be unable to use citrate as their sole carbon source, unable to decarboxylate the amino acid lysine, and urease negative.

Swimmer's ear, a form of external otitis is commonly caused by A. Acinetobacter baurnannii B. Bordetella bronchiseptica C. Haemophilus influenzae D. Pseudomonas aeruginosa

D. Swimmer's ear is a form of external otitis common to persons who swim and fail to completely dry their ear canals when they get out of the water. The organism most commonly associated with this condition is Pseudomonas aeruginosa. It is an organism known to be an opportunistic pathogen and one that favors a watery environment.

The classic toxigenic strains of which serogroup are implicated in epidemic infections of Vibrio cholerae? A. Ol B. O2 C. O3 D. O4

A. Classic epidemic strains of Vibrio cholerae are included in the antigenic O group 1. The Ogawa and Inaba strains are considered the predominant epidemic strains. In the last few years the strain O139 has also been associated with outbreaks of cholera.

The Haemophilus influenzas vaccine protects against which serotype? A. Serotype a B. Serotype b C. Serotype c D. Serotype d

B. Before the development of an effective vaccine, the strain of Haemophilus influenzae found to be implicated in the majority of cases of bacterial meningitis in children 1-6 years of age was serotype B. This serotype is surrounded by a weakly immunogenic polyribitol phosphate capsule. The widespread use of Haemophilus influenzae type b (Hib) vaccine beginning in 1985 has significantly reduced the incidence of invasive H. influenzae type b disease

The causative agent of melioidosis is A. Burkholderia cepacia B. Burkholderia pseudomallei C. Moraxella catarrhalis D. Stenotrophomonas maltophilia

B. Burkholderia pseudomallei is the causative agent of melioidosis. The bacterium is found in soil and water in subtropical areas of Southeast Asia and Australia. Melioidosis exhibits several forms, from skin abscesses to abscess formation in internal organs.

The majority of clinical isolates of Klebsiella are A. K. ozaenae B. K. pneumoniae C. K. aerogenes D. K. oxytoca

B. K. pneumoniae B. Klebsiella pneumoniae is the species most frequently recovered from the vast majority of clinical cases. Members of the genus Klebsiella have a capsule and appear mucoid on cultures. This highly encapsulated organism can cause severe pneumonia, nosocomial infections of several types, infantile enteritis, and other extraintestinal infections.

Which of the following is not true about Pasteurella multocida? A. Most common human infections occur in soft tissues, bones, and joints. B. Humans harbor the organism as part of their normal flora. C. It is the most virulent of the species in the genus. D. It grows on sheep blood agar.

B. Pasteurella multocida is the species in the genus most often encountered in the clinical laboratory. It is normal oral flora in animals, not humans, and it is an opportunistic pathogen. The mode of transmission generally involves traumatic inoculation of the organism through the skin. P. multocida grows on sheep blood agar but not on MacConkey agar.

Plesiomonas was recently moved to which family? A. Brucelleaceae B. Enterobacteriaceae C. Legionellaceae D. Vibrionaceae

B. Plesiomonas was previously in the family Vibrionaceae. Based on nucleic acid and antigenie studies, it was recently moved to the family Enterobacteriaceae. P. shigelloides is the only species in this genus. Infection in humans has manifested mainly as diarrheal diseases, and a waterborne mode of transmission is often the source.

An example of a halophilic microorganism is A. Morganella morganii B. Plesiomonasshigelloid.es C. Vibrio parahaemolyticus D. Yersinia pestis

C. Vibrio parahaemolyticus is classified as a halophilic Vibrio sp. requiring increased osmotic pressure, in the form of salt, for growth. This makes routine biochemical test media less than optimal because of their low NaCl content. Growth in the presence of 1 % NaCl but no growth in media without the added Na+ is the test for the differentiation of halophilic organisms. Marine water is the normal habitat of most Vibrio spp.

Vibrio vulnificus is a well-established human pathogen that is known to cause A. Gastroenteritis B. Pneumonia C. Pyelonephritis D. Wound infections

D. Vibrio vulnificus is a halophilic lactosefermenting organism. The isolate is associated with two distinct clinical conditions: primary septicemia and wound infection. Septicemia with this organism appears to be correlated in most cases with preexisting hepatic disease. Septicemia due to V. vulnificus characteristically produces a fulminant disease with a high mortality rate. Wound infection with this organism is usually associated with trauma and contact with a marine environment

Colonies that are said to resemble "droplets of mercury" are characteristic of A. Bordetella pertussis B. Burkholderia cepacia C. Campylobacter jejuni D. Yersinia pestis

A. Bordetella pertussis is the etiologic agent of pertussis, or whooping cough. On BordetGengou or Regan-Lowe agars, the organism forms small, round colonies that resemble mercury droplets. A nasopharyngeal swab is recommended as the optimal specimen for the recovery of this agent.

Milk has classically been the primary food associated with the transmission of some diseases, especially for those diseases of cattle transmissible to humans, such as A. Brucellosis B. Glanders C. Meliodosis D. Pontiac fever

A. Brucella infects cattle and may be transmitted to humans by the ingestion of contaminated milk or other dairy products. Milk is able to support the growth of many clinically significant microorganisms, which may often be ingested in unpasteurized dairy products. Meliodosis and glanders are caused by Burkholderia pseudomallei and B. mallei, respectively. Pontiac fever is caused by Legionella pneumoniae. None of these is transmitted by milk.

In suspected cases of brucellosis, what is the most sensitive specimen to submit for culture? A. Bone marrow B. Nasopharyngeal swab C. Sputum D. Stool

A. Brucella spp. are fastidious, gram-negative, coccobacillary organisms. They are predominantly animal pathogens, but occasionally produce disease in humans. The usual specimens for recovery of Brucella are blood and bone marrow, with the latter considered the more sensitive

An environmental sampling study of respiratory therapy equipment produced cultures of a yellow, nonfermentative (at 48 hours), gram-negative bacillus from several of the nebulizers, which would most likely be species of A. Chryseobacterium B. Pseudomonas C. Alcaligenes D. Moraxella

A. Chryseobacterium A. Chryseobacterium spp. are ubiquitous in the environment and are especially associated with moist soil and water. Chryseobacterium (formerly Flavobacterium) meningosepticum, a known nosocomial pathogen, has been implicated in outbreaks of meningitis in hospitals and is associated with the use of contaminated respiratory therapy equipment. Adult human infections are rare; these opportunistic microorganisms occur primarily in immunocompromised patients

Hemolytic uremic syndrome is a complication after infection with A. E. coli O157:H7 B. Salmonella Typhi C. Vibrio cholerae Ol D. Yersinia enterocolitica

A. E. coli O157:H7 produces a toxin similar to Shiga toxin produced by Shigella dysenteriae. It is most commonly transmitted by ingestion of undercooked ground beef or raw milk. Hemorrhagic colitis is characteristic of infection, but infection can also lead to hemolytic uremic syndrome resulting from toxin-mediated kidney damage.

Edwardsiella tarda is occasionally isolated in stool specimens and can biochemically be confused with A. Salmonella B. Enterohemorraghic E. coli C. Vibrio cholerae D. Yersinia enterocolitica

A. Edwardsiella tarda is a motile member of the family Enterobacteriaceae and as such is characteristically peritrichously flagellated. These organisms are infrequently isolated in the clinical laboratory. Biochemically they may initially resemble Salmonella in many ways, such as hydrogen sulfide production and the inability to ferment lactose.

Which of the following reactions is typical for Escherichia coli? A. Beta-hemolytic on sheep blood agar B. Colorless colonies on MacConkey agar C. Colorless colonies on xylose-lysinedesoxycholate agar D. Green colonies with black centers on Hektoen enteric agar

A. Escherichia coli is a lactose-fermenting member of the family Enterobacteriaceae. Various selective and differential agars are available for the differentiation of lactose fermenters from those that do not degrade lactose. In some media H7S production may be demonstrated. Isolates of E. coli would produce yellow colonies at 24 hours on xylose-lysine-desoxycholate (XLD) agar. Non-lactose fermenters such as Shigella would produce red colonies on XLD agar. On MacConkey agar, lactose fermenters produce pink colonies; on Hektoen enteric agar, colonies would be orange. Most strains of E. coli are beta-hemolytic on sheep blood agar.

Which of the following is not true of Shigella sonnei? A. Large numbers of organisms must be ingested to produce disease. B. The organism produces an inflammatory condition in the large intestine with bloody diarrhea. C. The organism produces disease most commonly in the pediatric population. D. The organism is a delayed lactose fermenter.

A. Large numbers of organisms must be ingested to produce disease A. Shigella has a low infecting dose and has been reported to cause outbreaks in daycare centers and can be spread to family members. These organisms are found in humans only at the time of infection; they are not part of the normal flora. Transmission is by the fecal-oral route, typically by ingestion of contaminated foods or water.

Legionella pneumophila A. Infections are most often acquired from environmental sources B. Metabolizes a number of carbohydrates C. Stains easily on the routine Gram stain D. Does not autofluoresce

A. Legionella pneumophila requires the use of special laboratory media for cultivation and does not stain well by the conventional Gram stain. Most Legionella spp. are motile, are biochemically inert, and autofluoresce.The primary mode of transmission is by the airborne route, usually in association with an environmental source of bacteria.

Which of the Neisseria spp. produces acid from glucose but not from maltose, lactose, or sucrose? A. Neisseria gonorrhoeae B. Neisseria lactamica C. Neisseria meningitidis D. Neisseria sicca

A. Neisseria gonorrhoeae is identified in the clinical laboratory by its ability to ferment only glucose. The diagnosis of the sexually transmitted disease caused by this agent can be definitively made only by the isolation and identification of N. gonorrhoeae in the clinical laboratory. Morphologically, all members of the genus are alike, and all are oxidase positive, which makes definitive identification procedures necessary. Nucleic acid amplification tests are also used frequently to diagnose gonorrhea.

Which of the following is true of Neisseria gonorrhoeae ? A. Adversly affected by fatty acids in clinical specimens B. Rapid growth on sheep blood agar C. Ferments glucose and maltose D. ONPG positive

A. Neisseria gonorrhoeae is the causative agent of gonorrhoea and is very sensitive to drying, temperature variations, and fatty acids in clinical material. N. gonorrhoeae will grow on chocolate agar but not sheep blood agar. Incubation under CO2 is required for recovery, and selective media like Thayer-Martin are recommended.

A gram-negative, "kidney bean" cellular morphology is a distinguishing characteristic of A. Neisseria meningitidis B. Yersinia pestis C. Bartonella spp. D. Actinobacter spp

A. Neisseria meningitidis and N. gonorrhoeae are most commonly described as having a "kidney bean" cellular morphology. Occasionally some Moraxella spp. will exhibit this morphology. These gram-negative coccal organisms appear characteristically as diplococci, with the paired cells having adjacent walls that are flattened. Neisseria are important human pathogens

Pyocyanin is characteristically produced by A. Pseudomonas aeruginosa B. Pseudomonasfluorescens C. Shewanella putrefaciens D. Stenotrophomonas maltophillia

A. Pyocyanin is the nonfluorescent, blue-green, diffusable pigment produced by Pseudomonas aeruginosa. It is the only bacterium able to produce this pigment. Pyocyanin mixes with the yellow pigment fluorescein to turn culture media green. Most P. aeruginosa strains can be identified presumptively by their characteristic grapelike odor, colony morphology, and blue-green pigment.

The enterotoxins of both Vibrio cholerae Ol and noninvasive (toxigenic) strains of Escherichia coli produce serious diarrhea by what mechanism? A. Stimulation of adenylate cyclase, which gives rise to excessive fluid secretion by the cells of the small intestine B. Penetration of the bowel mucosa C. Stimulation of colicin production D. Elaboration of a dermonecrotizing toxin

A. Stimulation of adenylate cyclase, which gives rise to excessive fluid secretion by the cells of the small intestine A. Enterotoxins are produced in the intestinal tract and primarily cause diarrhea. The heatlabile enterotoxin of Escherichia coli, which resembles cholera toxin, acts to stimulate the enzyme adenylate cyclase. The stimulation of the enzyme adenylate cyclase by the toxin increases the production of cyclic AMP, causing rapid gastrointestinal fluid loss. Diarrhea results following stimulation of the secretion of chloride ions by the cells lining the small intestine.

A positive indole reaction is characteristic of A. Escherichia coli B. Proteus mirabilis C. Salmonella Choleraesuis D. Serratia marcescens

A. The indole reaction is a widely used method for differentiating lactose-positive Escherichia coli from other members of the family Enterobacteriaceae. Organisms such as E. coli, which possess the enzyme tryptophanase, are able to metabolize the amino acid tryptophan with the production of indole, pyruvic acid, and ammonia. Indole represents the "I" in the IMViC reactions, a battery of tests used for the identification of the Enterobacteriaceae

The etiologic agent of whooping cough is A. Bordetella pertussis B. Brucella suis C. Francisella tularensis D. Haemophilus ducreyi

A. Whooping cough, or pertussis, is caused by Bordetella pertussis, a minute, encapsulated, nonmotile, gram-negative, pleomorphic bacillus. The best identification method is the polymerase chain reaction. Regan-Lowe medium is recommended for the isolation of this agent.

Fecal cultures are inoculated on thiosulfate-citrate-bile salts-sucrose agar specifically for the isolation of A. Shigella B. Vibrio C. Campylobacter D. Salmonella

B. A highly selective medium, thiosulfate-citratebile salt-sucrose (TCBS) is used for the isolation of Vibrio spp. Species able to ferment sucrose, such as V. cholerae, produce yellow colonies. Non-sucrose-fermenting organisms produce green colonies.

Which of the following is not appropriate for the cultivation of Neisseria gonorrheae? A. Chocolate agar B. Cefsulodin-irgasan-novobiocin agar C. Martin-Lewis agar D. Modified Thayer-Martin agar

B. A variety of media has been developed to aid in the isolation of Neisseria gonorrhoeae from specimens containing mixed flora. Examples include Martin-Lewis, modified Thayer-Martin, GC-Lect, and New York City media. The most commonly used nonselective medium for the isolation of N. gonorrhoeae is chocolate agar. Cefsulodin-irgasan-novobiocin (CIN) is a selective and differential medium for the isolation of Yersinia enterocolitica and Aeromonas.

The species of Campylobacter noted to produce septicemia, septic arthritis, meningitis, jaundice with hepatomegaly, and thrombophlebitis in debilitated patients is A. C. coli B. C. fetus C. C. laris D. C. sputorum

B. Campylobacter fetus subsp. fetus is occasionally implicated in human disease. This organism, unlike C. jejuni, is characterized as producing extraintestinal symptoms. Those persons most at risk of infection are those with preexisting disease who are in a debilitated condition.

Campylobacter spp. are associated most frequently with cases of A. Osteomyelitis B. Gastroenteritis C. Endocarditis D. Appendicitis

B. Campylobacter jejuni rivals Salmonella as the most common bacterial cause of diarrheal disease in humans. Campylobacter enterocolitis is characterized by fever, bloody diarrhea, and abdominal pain. Special selective culture media and incubation under a microaerophilic atmosphere at 42°C are required for the recovery of this organism from clinical samples.

Which of the the following is not true of Haemophilus spp.? A. Obligate parasites B. Grow well on sheep blood agar C. Small, pleomorphic, gram-negative coccobacilli D. Many are found as normal flora in the human respiratory tract.

B. Chocolate agar is the preferred culture medium for Haemophilus. Unlike 5% sheep blood agar, it provides both hemin (X factor) and NAD (V factor) required for growth. H. ducreyi grows best in a special medium, Mueller-Hinton-based chocolate agar, supplemented with 1% IsoVitaleX and 3 |ag/mL of vancomycin. Haemophilus spp. are obligate parasites of animals and are found primarily in the upper respiratory tract and oral cavity.

Which of the following is not true about the laboratory diagnosis of pertussis? A. Regan-Lowe medium is the recommended medium. B. DFA test results are definitive and do not need to be confirmed by culture. C. Calcium alginate or Dacron swabs are recommended over cotton-tipped swabs for specimen collection. D. Material collected from the nasopharynx is optimal for detection of the causative agent.

B. Direct fluorescent antibody (DFA) test results for Bordetella pertussis are rapid but presumptive. Both positive and negative test results must be confirmed by culture. The quality of the test result depends greatly on the experience of the microscopist, the quality of the antibody, and the microscope. Material collected from thenasopharnyx with calcium alginate swabs for DFA and culture is recommended.

One of the most common etiologic agents of community-acquired uncomplicated cases of cystitis is A. Enterobacter aerogenes B. Escherichia coli C. Klebsiella pneumoniae D. Proteus vulgaris

B. Escherichia coli is frequently the etiologic agent of community-acquired cystitis. This agent can be easily recognized by its fermentation of lactose, negative citrate reaction, and positive indole test. On eosin methylene blue agar, Escherichia coli produces characteristic dark colonies with a metallic sheen.

Why are cultures for Gardnerella vaginalis not recommended? A. The bacteria grow so slowly that results take too long to be relevant. B. Isolation of the bacteria may not be clinically significant. C. It is unsafe to grow this bacterium. D. Artificial media are not available.

B. Gardnerella vaginalis is associated with bacterial vaginosis, but cultures are not recommended for diagnosis. Many women carry G. vaginalis as normal vaginal flora; therefore, the isolation of the organism may not be clinically significant. The disease can be diagnosed by detecting "clue" cells, vaginal epithelial cells with gram-variable bacilli attached to their surface.

Infection of the gastric mucosa leading to gastritis or peptic ulcers is most commonly associated with A. Campylobacter jejuni B. Helicobacter pylori C. Salmonella Typhi D. Shigella sonnet

B. Helicobacter pylori is found in the human gastric mucosa colonizing the mucous layer of the antrum and fundus but does not invade the epithelium. Approximately 50% of adults over the age of 60 years are infected, with the incidence of gastritis increasing with age. H. pylori has been cultured from feces and dental plaque, supporting the theory of a fecal-oral or oral-oral route of transmission.

The organism that is linked to peptic ulcers and is the most frequent cause of gastritis is A. Campylobacter jejuni B. Helicobacter pylori C. Salmonella Typhimurium D. Yersinia enterocolitica

B. Helicobacter pylori is implicated as an etiologic agent of gastritis and peptic ulcer disease. This organism can be demonstrated in gastric biopsy specimens. H. pylori produces a strong positive urease test result.

Foodborne outbreaks of brucellosis are most commonly associated with eating A. Raw shellfish B. Imported cheese C. Contaminated potato salad D. Improperly cooked hamburger

B. Ingestion of contaminated unpasteurized (raw) milk or cheese is one of the primary routes of infection. Brucellosis is found worldwide, and symptoms vary from asymptomatic to a debilitating systemic infection. Only four of the six species are typically pathogenic for humans: B. abortus, B. melitensis, B. suis, and B. canis.

A young man developed keratitis associated with the use of contact lenses that had been immersed in a contaminated cleaning solution. The most common bacterial etiologic agent in such cases is A. Chiyseobacterium meningosepticum B. Pseudomonas aeruginosa C. Francisella tularensis D. Escherichia coli

B. Keratitis is a serious clinical condition that is characterized by inflammation of the cornea, which, if not appropriately treated, may lead to loss of vision. Pseudomonas aeruginosa is the most common agent of bacterial keratitis associated with lens-cleaning solution. Pseudomonads are opportunistic pathogens that are commonly associated with contaminated fluids.

Kingella denitrificans can be differentiated from Neisseria gonorrhoeae because it is A. Able to grow on Thayer-Martin agar B. Able to reduce nitrates C. Oxidase positive D. Glucose positive

B. Kingella denitrificans is most often associated with endocarditis. It is morphologically similar to Neisseria gonorrhoeae both on Gram stain and colonies on culture media. Confusion is further compounded by its ability to grow on modified Thayer-Martin medium and its positive oxidase and glucose reaction. The ability of K. denitrificans to reduce nitrates is a key test for its differentiation from N. gonorrhoeae.

Which of the following is not a characteristic of Klebsiella (Calymmatobacteriuni) granulomatis? A. Is often sexually transmitted B. Is isolated on chocolate agar C. Is the causative agent of granuloma inguinale D. Can be diagnosed by detection of Donovan bodies in clinical specimens

B. Klebsiella granulomatis, formerly Calymmatobacterium granulomatis, is the etiologic agent of the sexually transmitted disease granuloma inguinale. It is a pleomorphic, gram-negative, encapsulated bacillus, although it does not Gram stain well. First seen as inclusions (Donovan bodies) in mononuclear cells from genital ulcers stained with the Giemsa or Wright stain, these organisms are extremely difficult to recover.

Lack of motility is a characteristic of A. Enterobacter B. Klebsiella C. Salmonella D. Serratia

B. Klebsiella spp. are all nonmotile, which aids in their identification. Klebsiella spp. produce a capsule resulting in mucoid colonies. Shigella, another genus in the family Enterobacteriaceae, is also nonmotile.

Buffered charcoal yeast extract agar is the recommended medium for the recovery of A. Hafnia alvei B. Legionella pneumophila C. Neisseria meningitidis D. Vibrio cholerae

B. Legionella pneumophila, the causative agent of Legionnaires disease, can be recovered from respiratory tract secretions. The bacterium is fastidious and, like Francisella tularensis, requires cystiene or cystine for growth. The culture medium most commonly recommended is buffered charcoal yeast extract (BCYE) agar, which is incubated in a moist chamber at 35°C. Growth on this medium may not be visible for 3 to 4 days, after which further identification procedures may be carried out.

Besides Pseudomonas aeruginosa, which of the following is an important cause of lower respiratory tract infections in patients with cystic fibrosis? A. Actinobacillus actinomycetemcomitans B. Burkholdia cepacia C. Chiyseobacterium meningosepticum D. Serratia marcescens

B. Like Pseudomonas aeruginosa, Burkholderia cepacia is a ubiquitous opportunistic organism. Although P. aeruginosa is by far the most important cause of lower respiratory tract infections in patients with cystic fibrosis, B. cepacia is also a significant cause of morbidity. Both of these bacteria are oxidase positive and will grow on MacConkey agar. P. aeruginosa typically produces a green discoloration of the medium it is grown on.

Legionella pneumophila is the etiologic agent of both Legionnaires disease and A. Swine fever B. Pontiac fever C. Rift Valley fever D. San Joaquin Valley fever

B. Pontiac fever is caused by Legionella pneumophila, as is Legionnaires disease, but it is not as serious an infection. This febrile illness is characteristically self-limited and does not demonstrate significant pulmonary symptoms. The incubation period, unlike that for Legionnaires disease, is short, followed by symptoms of malaise, muscle aches, chills, fever, and headache.

Association with faucet aerators and humidifiers used with ventilators in intensive care units is commonly a factor in outbreaks of infections with which of the following microorganisms? A. Klebsiella pneumoniae B. Pseudomonas aeruginosa C. Salmonella spp. D. Serratia marcescens

B. Pseudomonas aeruginosa is a major cause of hospital-acquired infections. These opportunistic organisms are able to survive in moist environments for prolonged periods and may be transferred to immunocompromised patients. Pseudomonas infections in recent years have accounted for as much as 10% of nosocomial infections.

The characteristic growth pattern known as "satelliting" is associated with A. BurkhoIderia pseudomallei B. Campylobacterjejuni C. Haemophilus influenzas D. Yersinia pestis

C. "Satellitism" is the name given to the appearance of colonies of Haemophilus influenzae on sheep blood agar medium around colonies of organisms that provide an essential growth factor. H. influenzae requires both hemin and NAD. Colonies of some organisms, such as Staphylococcus and Neisseria, produce NAD, which diffuses into the surrounding agar and enables H. influenzae to grow.

Which of the following is not a correct description regarding Aeromonas hydrophila? A. Beta-hemolytic B. Catalase positive C. ONPG negative D. Oxidase positive

C. Aeromonas can be differentiated from many other fermentative gram-negative bacilli, such as the Enterobacteriaceae, in that they are oxidase positive. Isolates are ONPG and catalase positive. On sheep blood agar medium, colonies are beta-hemolytic. A. hydrophila is found in soil and water and has been isolated from a variety of human infections.

Which of the following nonfermenters is rarely isolated in the U.S.? A. Pseudomonas aeruginosa B. Stenotrophomonas maltophilia C. Burkholderia mallei D. Burkholderia cepacia

C. B. cepacia is the most common Burkolderia spp. in clinical specimens. P. aeruginosa is the most common gram-negative bacillus that is not in the family Enterobacteriaceae and Stenotrophomonas maltophilia the second most common. B. mallei has not been isolated recently in the U.S.

Which of the following is the most common indicator of bacterial vaginosis? A. Eikenella B. Capnocytophaga C. Gardnerella D. Listeria

C. Gardnerella vaginalis is associated with cases of bacterial vaginosis (B V) formerly called "nonspecific vaginitis." Although G. vaginalis is probably not involved in the pathogenesis of B V, its presence in high numbers is considered a presumptive diagnosis. These small, gram-negative bacilli are frequently seen in great numbers on the surface of epithelial cells ("clue cells") taken from the vagina

Color Plate 28 • shows the Gram stain of cerebrospinal fluid from a 1-year-old girl suspected of having meningitis. After 24 hours of growth, small tan colonies were isolated on chocolate agar incubated in CO2. Sheep blood agar also incubated in CO2 had no growth. Which of the following organisms should be suspected? A. Brucella canis B. Bordetella parapertussis C. Haemophilus influenzae D. Neisseria meningitidis

C. Color Plate 28 • is a Gram stain of a cerebrospinal fluid specimen revealing many white blood cells. All of the bacteria listed are fastidious; however, Haemophilus influenzae would be expected to grow on chocolate agar but not sheep blood agar (SBA). Neisseria meningitidis, also an important cause of meningitis, would be expected to grow on SBA incubated in CO2. Bordetella parapertussis and Brucella sp. would likely grow on both SBA and chocolate agar, and both are uncommon isolates.

Colonies of Neisseria sp. turn color when a redox reagent is applied. The color change is indicative of the activity of the bacterial enzyme A. Beta-galactosidase B. Urease C. Cytochrome oxidase D. Phenylalanine deaminase

C. Cytochrome oxidase C. The genus Neisseria contains organisms that possess cytochrome oxidase activity. Colonies can be identified by the development of a dark purple color following the application of tetramethyl-p-phenylenediamine dihydrochloride. The reaction relies on the property of the molecule to substitute for oxygen as an electron acceptor. In the presence of the enzyme and atmospheric oxygen, the molecule is oxidized to form indophenol blue

Production of a yellow pigment is characteristic of which of the following Enterobacter sp.? A. E. aerogenes B. E. cloacae C. E. sakazakii D. E. taylorae

C. Enterobacter sakazakii produces a yellow pigment that aids in its presumptive identification. Some strains of E. cowanii are also pigmented. E. sakazakii is an occasional clinical isolate that has been linked to respiratory tract infections and wounds

Which of the following has a negative oxidase test? A. Aeromonas B. Chryseobacterium C. Hafnia D. Vibrio

C. Hafnia alvei is a member of the family Enterobacteriaceae and is oxidase negative. It has been isolated from a variety of clinical specimens but is generally considered clinically insignificant. Aeromonas, Chryseobacterium, and Vibrio are all oxidase positive.

Which of the following organisms is unable to grow on MacConkey agar? A. Bordetella bronchiseptica B. Burkholderia cepacia C. Kingella denitrificans D. Plesiomonas shigelloides

C. Kingella spp. are gram-negative bacilli or coccobacilli that may appear in short chains. K. denitrificans can be isolated from the human upper respiratory tract, will grow on modified Thayer-Martin agar, and is oxidase-positive. The growth of this organism is inhibited by MacConkey agar, and growth is poor on triple sugar iron agar.

Of the following microorganisms, which one will turn a dark purple when tetramethyl-p-phenylenediaminehydrochloride is applied? A. Acinetobacter baumannii B. Stenotrophomonas maltophilia C. Moraxella catarrhalis D. Yersinia enterocolitica

C. Moraxella catarrhalis possesses the enzyme indophenol oxidase. When a 1% solution of tetramethyl-p-phenylenediamine (oxidase reagent) is applied to colonies of these organisms, the colonies turn a purple color, which rapidly darkens. The other species listed are oxidase negative.

The flattened adjacent sides of the cellular appearance of which microorganism are said to resemble kidney beans? A. Aeromonas hydrophila B. Campylobacter jejuni C. Neisseria gonorrhoeae D. Pasteurella multocida

C. Neisseria gonorrhoeae is said to resemble a kidney bean on Gram stain because of its characteristic gram-negative diplococcal morphology in which the adjacent sides are flattened. Typically these organisms are found intracellularly when direct smears of clinical material are examined.Smears from the female genital tract must be interpreted with caution, however, because other normal flora microorganisms are morphologically similar.

Which of the Neisseria spp. produces acid from glucose and maltose but not sucrose or lactose? A. Neisseria gonorrhoeas B. Neisseria lactamica C. Neisseria meningitidis D. Neisseria sicca

C. Neisseria meningitidis is a human pathogen most commonly associated with meningitis. These oxidase-positive, gram-negative diplococci are identified either by fermentation tests or serologic methods that use specific antisera. N. meningitidis ferments both glucose and maltose.

When an epidemiologic survey for the detection of upper respiratory tract earners of Neisseria meningitidis or Bordetella pertussis is being conducted, the optimal type of specimen to be obtained for culture is A. Anterior nares B. Buccal cavity C. Nasopharyngeal D. Throat

C. Neisseria meningitidis is the etiologic agent of one form of inflammation of the meninges, known as epidemic cerebrospinal meningitis. Infection with Bordetella pertussis produces the highly contagious upper respiratory infection pertussis. Both diseases are spread by droplet infection or fomites contaminated with respiratory secretions. The microorganisms are present in greatest numbers in the upper respiratory tract, and specimens for isolation and identification should be collected on nasopharyngeal swabs.

Which of the following is not true regarding virulent strains of Vibrio cholerae? A. Adherent to enterocytes B. Mucinase production C. Nonmotile D. Toxigenic

C. Pathogenic mechanisms of V. cholerae include adherence to enterocytes via pili, motility, enzymes such as protease and mucinase, and the production of an enterotoxin. Epidemic strains colonize the small intestine where they elaborate choleragen, an enterotoxin. Disease is produced when the enterotoxin stimulates the secretion of large volumes of fluids into the intestinal lumen.

In cases of legionellosis A. Person-to-person transmission is common B. Farm animals are important animal reseroirs C. Patients can present with a self-limited nonpneumonic febrile illness D. Specimens may be cold enriched to enhance recovery of the organism

C. Pneumonic legionellosis and the nonpneumonic illness known as Pontiac fever are the two clinical forms of disease caused by Legionella pneumophila. The optimal temperature for cultivation is 35°C, and cold enrichment is not appropriate. Direct fluorescent antibody is often used diagnostically, and erythromycin is the drug of choice for therapy.

A positive phenylalanine deaminase reaction is characteristic of A. Hafiiia alvei B. Moraxella catarrhalis C. Proteus vulgaris D. Salmonella Enteritidis

C. Proteus vulgaris is able to deaminate phenylalanine. The test is performed by inoculating the isolate on a slant of medium containing phenylalanine and, after incubation, adding a 10% solution of ferric chloride. A dark green color on the slant after addition of the reagent is a positive result.

Pus was aspirated from an empyema. A Gram stain of the aspirated material showed many white blood cells and numerous gram-negative bacilli. The culture grew many colonies producing a soluble green pigment. The most likely etiologic agent in this case would be A. Chromobacterium violaceum B. Legionella pneumophila C. Pseudomonas aeruginosa D. Serratia marcescens

C. Pseudomonas aeruginosa has not only a characteristic grapelike odor but also a bluegreen color. These oxidative, motile organisms are oxidase positive and are able to grow at 42°C. In humans these opportunistic organisms cause many types of infections, but they are primarily associated with burn wound infections.

Chronic carriers, persons who remain infected with an organism for long periods, are typically associated with the dissemination of A. Bordetella pertussis B. Campylobacter jejuni C. Salmonella Typhi D. Yersinia pestis

C. Salmonella Typhi is commonly spread by chronic carriers. Without treatment, this enteric bacillus can be carried throughout a person's lifetime and is sequestered most often in the gallbladder. Carriers are usually asymptomatic, and the presence of the organism can be confirmed only by isolation and identification in the clinical laboratory

Which of the following is not an appropriate medium for primary isolation of Bordetella pertussis ? A. Regan-Lowe B. Bordet-Gengou C. Modified Skirrow's medium D. Buffered charcoal yeast extract

C. The diagnosis of pertussis, or whooping cough, is confirmed by culture. Regan Lowe, a charcoal-based medium, provides the best results. Cephalexin is often added to make the medium selective. Isolation of the etiologic agent is best done within the first week of the illness. Modified Skirrow's medium is a primary plating media for Campylobacter spp

In the past, povidone iodine, tincture of iodine prep pads and swabs, and other disinfectants have been recalled because of microbial contamination. The most likely organism to be isolated in these cases is A. Bordetella bronchiseptica B. Klebsiella pneumoniae C. Pseudomonas aeruginosa D. Serratia marcescens

C. The recalls described illustrate the ubiquitous nature of Pseudomonas aeruginosa in the environment and its resistance to many disinfectants. In addition, the bacterium has minimal nutritional requirements and the ability to tolerate a wide range of temperatures (4-42°C). P. aeruginosa is an opportunistic pathogen commonly associated with hospital-acquired infections.

The symptom of diffuse, watery diarrhea that produces a relatively clear stool containing mucus flecks is suggestive of an infection caused by A. Enterohemorrhagic Escherichia coli B. Shigella dysenteriae C. Vibrio cholerae D. Yersinia enterocolitica

C. Vibrio cholerae produces an exotoxin that causes infected individuals to lose massive amounts of fluids. Severe dehydration is usually the cause of death in untreated patients. Proper therapy begins with intravenous fluids to restore the patient's water volume and electrolyte balance. The microorganism does not invade the intestinal mucousa but is attached to the surface of enterocytes. The other bacteria listed produce toxins or invasive diseases that often produce inflammation resulting in bloody diarrhea.

Brucella spp. are A. The etiologic agents of relapsing fever B. Small spiral organisms C. Primarily a cause of endogenous human infections D. Intracellular pathogens

D. Brucella spp. are small, gram-negative intracellular parasites implicated in zoonotic infection of humans. Brucellosis presents as an undulant febrile illness. In the U.S., disease caused by Brucella sp. is mainly job related or involves food or animal associations, such as in hunters or those who drink raw milk.

Which of the following is true concerning Campylobacter jejuni ? A. Catalase negative B. Isolated best at 24°C C. Hydrogen sulfide positive D. A leading cause of bacterial diarrhea worldwide

D. Campylobacter jejuni is an important human pathogen most commonly associated with cases of bloody diarrhea, fever, and abdominal pain in humans. Special handling of cultures suspected to contain this organism is required for optimal recovery. Cultures should be incubated at 42°C in a microaerophilic atmosphere and examined at 24 and 48 hours for spreading nonhemolytic colonies, which may be slightly pigmented. Wet mounts demonstrate the typical "darting" motility of this isolate.

Which of the following is not characteristic of Eikenella corrodens? A. It is a thin, gram-negative bacillus. B. Colonies sometimes pit the surface of the agar medium. C. It is found in the mouth and upper respiratory tract of humans. D. It is often found in pure culture when recovered from infections.

D. Eikenella corrodens is a facultatively anaerobic gram-negative bacillus that requires hemin in the culture medium to grow aerobically. This organism, which is a part of the normal indigenous flora of humans, is seldom found in pure culture. It is commonly associated with polymicrobial infections following bite or clenched-fist wounds. Infections of the face and neck may also involve this organism, which produces pitting of the agar on which it is isolated.

Which of the following is not characteristic of Haemophilus influenzae biogroup aegyptius? A. Indole negative B. Requires V factor C. Requires X factor D. Aminolevulinic acid positive

D. Haemophilus influenzae biogroup aegyptius causes a conjunctivitis followed by invasive disease known as Brazilian purpuric fever. The bacterium requires both X and V factors and is therefore negative for delta-aminolevulinic acid (ALA). It resembles H. influenzae biotype III in that it is indole negative, urease positive, and ornithine decarboxylase negative

Which of the following Legionella spp. is positive for hippurate hydrolysis? A. L. micdadei B. L. longbeachae C. L. gormanii D. L. pneumophila

D. Legionella pneumophila is able to hydrolyze hippurate. L. pneumophila will also autofluoresce. Although most of the studies done on legionellosis are based on this species, L. pneumophila is not the only one associated with human disease.

Which of the following organisms would most likely produce the biochemical reactions shown in Color Plate 27 •? A. Citrobacterfreundii B. Proteus mirabilis C. Providencia rettgeri D. Salmonella

D. Most serotypes of Salmonella produce hydrogen sulfide in triple sugar iron agar. As seen in Color Plate 27 •, they demonstrate a positive lysine and a negative urease reaction, which differentiates them from Proteus spp., which also produce H2S. It is important to be able to quickly differentiate those organisms resembling Salmonella from other H2S-producing organisms such as Citrobacter freundii and Edwardsiella tarda.

New York City agar was developed for the isolation of A. Bordetella pertussis B. Campylobacter fetus C. Haemophilus influenzae D. Neisseria gonorrhoeae

D. New York City (NYC) medium was developed by the New York City Public Health Laboratory for the isolation of Neisseria gonorrhoeae. It is a horse serum-based medium that is selective by the addition of colistin, vancomycin, and amphotericin B. Modified Thayer-Martin, another commonly used selective medium for N. gonorrhoeae, is chocolate based.

Erythromycin eye drops are routinely administered to infants to prevent infections by A. E. coli B. Haemophilus influenzae C. Pseudomonas aeruginosa D. Neisseria gonorrhoeae

D. Ophthalmia neonatorum, a form of conjunctivitis, is associated with Neisseria gonorrhoeae. The infection is transmitted to the newborn by the mother as it passes through the birth canal. The use of an ophthalmic solution of erythromycin is recommended for the prevention of this form of conjunctivitis.

The optimal specimen for the recovery of Bordetella pertussis is A. Anterior nares swab B. Blood C. Expectorated sputum D. Nasopharyngeal swab

D. Posterior nasopharyngeal cultures are recommended for the recovery of Bordetella pertussis in suspected cases of pertussis (whooping cough). Swabs of the nasopharynx are inoculated on the selective agar Regan-Lowe. Cephalexin is added to the culture medium to inhibit the growth of contaminating indigenous flora.

Which of the following diseases is most likely to be acquired from a hot tub or whirlpool? A. Q fever B. Erysipelas C. Acinetobacter cellulitis D. Pseudomonas dermatitis

D. Pseudomonads are ubiquitous microorganisms generally associated with moist environments. Cases have been increasing as the popularity of health spas increases. In some cases the pattern of dermatitis caused by these organisms matches the areas covered by the individual's swimsuit. When not properly maintained, whirlpools create a favorable environment for the growth of these organisms.

An example of an oxidase-positive, glucose nonfermenting organism is A. Aeromonas hydrophila B. Escherichia coli C. Klebsiella pneumoniae D. Pseudomonas aeruginosa

D. Pseudomonasa aendgnosa is the most commonly encountered gram-negative species that is not a member of the family Enterobacteriaceae. It is ubiquitous in nature and is found in homes and hospitals. It is an opportunistic pathogen responsible for nosocomial infections.

A positive gelatin reaction is characteristic of A. Morganella morganii B. Proteus vulgar is C. Salmonella Typhimurium D. Serratia liquefaciens

D. Serratia liquefaciens, as its name implies, is able to liquefy gelatin. This bacterium is not thought to be a primary pathogen and is onlyrarely isolated from clinical specimens. The positive arabinose reaction is one way of differentiating this isolate from Serratia marcescens.

Severe disseminated intravascular coagulation often complicates cases of septicemia caused by A. Acinetobacter sp. B. Moraxella sp. C. Neisseria gonorrhoeae D. Neisseria meningitidis

D. The Waterhouse-Friderichsen syndrome of disseminated intravascular coagulation occurs in cases of fulminant meningococcemia—Neisseria meningitidis septicemia. Invasion of the circulatory system by N. meningitidis may produce only a transient bacteremia or meningitis or may go on to cause a rapidly fatal infection. In cases of meningococcemia with intravascular coagulation, acute adrenal insufficiency due to hemorrhage into the adrenal gland may result.

Which of the the following does not describe Acinetobacter sp.? A. Commonly susceptible to most antimicrobials B. Generally coccobacillary in morphology C. Oxidase negative D. Infections associated with use of medical devices

A. Acinetobacter is widely distributed in nature and commonly colonizes hospitalized patients. Infection occurs mainly in compromised hosts. Its resistance to many of the commonly used antimicrobial agents limits the selection of therapeutic agents.

Violet-colored colonies are typically produced by A. Chromobacterium violaceum B. Chryseobacterium meningosepticum C. Pseudomonas aeruginosa D. Serratia marcescens

A. Chromobacterium violaceum is a motile, gram-negative bacillus found in soil and water that can be pathogenic for humans. The production of a non-water-soluble violet pigment by these organisms aids in their identification. Chromobacterium is catalase and oxidase positive and generally attacks carbohydrates fermentatively.

Eikenella corrodens is an opportunistic pathogen, but it is most noted for causing A. Abscesses of the oral cavity B. Pneumonia C. Postsurgical wound infections D. Urinary tract infections

A. Eikenella corrodens can be normal flora of the oral cavity of humans. It is a weak pathogen that is associated with polymicrobial abscesses of the oral cavity. E. corrodens will grow on sheep blood and chocolate agars. Some strains will produce pitting of the agar.

Haemophilus ducreyi is the causative agent of A. Chancroid B. Lymphogranuloma venereum C. Trachoma D. Whooping cough

A. Haemophilus ducreyi is the causative agent of chancroid, a serious sexually transmitted disease. The disease is more prevalent in the tropics than in temperate parts of the world. The bacteria produce buboes in the groin and can cause a septicemia.

The selective nature of Hektoen enteric agar is due to the inclusion of which one of the following? A. Bile salts B. fiz's'-sodium metasulfate C. Bromthymol blue D. NaCl

A. Hektoen enteric agar was developed to improve the isolation of Shigella and Salmonella from stool specimens. The selective nature of this agar is due to bile salts. The medium also contains three carbohydrates—lactose, sucrose, and salicin—along with a pH indicator to detect carbohydrate fermentation. Fermentative organisms turn the medium yellow. Ferric ammonium citrate and sodium thiosulfate are included in the medium to detect H2S production. H2Sproducing organisms appear as black-centered colonies.

Which of the following is not urease positive? A. Salmonella B. Helicobacter pylori C. Proteus mirabilis D. Yersinia enterocolitica

A. Salmonella is urease negative and H2S positive. The negative urease reaction would help to differentiate it from an H2S-positive Proteus spp. Yersinia enterocolitica and Y. pseudotuberculosis are both urease positive. A rapid positive urease is a key test for the identification of H. pylori.

Some strains of Serratia marcescens produce a red-colored pigment. Pigment production is enhanced by A. Incubation at 22°C B. Incubation at 42°C C. Growth on sheep blood agar D. Growth on typtic soy agar without blood

A. Serratia marcescens is a chromogenic member of the family Enterobacteriaceae. S. marcescens is the most clinically significant of the genus and is frequently involved in nosocomial infection. The red pigment produced is not water soluble and is demonstrated more readily by incubation at room temperature than at 35°C

The K antigen of the family Enterobacteriaceae is A. Heat labile B. The somatic antigen C. Located on the flagellum D. The antigen used to group Shigella

A. The K (capsule) antigen surrounds the bacterial cell and masks the somatic antigens of the cell wall, which are used to group members of the Enterobacteriaceae. These heat-labile antigens can be removed by heating a suspension of the culture at 100°C for 10-30 minutes. Antisera that contain K antibody can be used to demonstrate the presence of the capsular antigens.

A positive Voges-Proskauer reaction is characteristic of A. Enterobacter aerogenes B. Escherichia coli C. Proteus vulgaris D. Providencia rettgeri

A. The Voges-Proskauer (VP) test is a broth test that detects the presence of acetoin from the metabolism of glucose in the medium. A red color indicates a positive reaction. The most common clinical isolates from the genera Providencia, Escherichia, Salmonella, and Proteus are generally VP negative, whereas most members of the Klebsiella, Enterobacter, and Serratia are positive. Enterobacteriaceae that are VP positive are typically methyl red negative.

In suspected cases of brucellosis, the optimal specimen to be collected for the isolation of the etiologic agent is A. Blood B. Urine C. Cerebrospinal fluid D. Nasopharyngeal exudates

A. The etiologic agents of brucellosis are the brucellae, which are small, nonmotile, gramnegative coccobacilli that are facultative intracellular parasites. Isolation of these organisms is difficult. In suspected cases, which are generally job related, multiple blood cultures are recommended for optimal recovery of the agent. Bone marrow cultures have been found to be positive when cultures of blood failed to recover the organism.

When performing the oxidase test, which of the following would not be appropriate? A. The reagent used is o-nitrophenyl-(3-D-galactopyranoside. B. A nichrome wire loop should be used to acquire inoculum for testing. C. Colonies from sheep blood agar can be used. D. A positive colony turns dark purple within 10 seconds after application of the reagent

A. The oxidase test detects those organisms that produce the enzyme cytochrome oxidase. A 1% solution of dimethyl- or tetra-methyl-p-phenylenediamine dihydrochloride is applied to filter paper, and the test organism is then rubbed into the impregnated area. Because Nichrome wire may cause a false-positive result, a platinum or plastic loop or wooden applicator stick should be used to pick the colony. The rapid development of a dark purple color in the area where the organism was inoculated is a positive oxidase test.

For the selective isolation of Vibrio spp. the recommended agar is A. Thiosulfate-citrate-bile salt-sucrose agar B. Charcoal yeast extract agar C. Mannitol salt agar D. Tinsdale agar

A. Thiosulfate-citrate-bile salt-sucrose (TCBS) agar is recommended for use in the selective isolation of Vibrio spp. associated with cholera, diarrhea, or food poisoning. The selective agent in this medium to inhibit gram-positive organisms is oxgall, a naturally occurring substance containing bile salts and sodium cholate. Sucrose is the carbohydrate in the medium. V cholerae and V. alginolyticus ferment sucrose and appear as large yellow colonies. V. parahemolyticus is unable to ferment sucrose and exhibits colonies with blue to green centers.

Isolation of Neisseria gonorrhoeae A. Is enhanced by cold enrichment B. Requires incubation under increased CO2 C. From contaminated sites is made easier by the use of CIN agar D. Is not affected if clinical specimen is refrigerated before culturing

B. Neisseria gonorrhoeae is a fastidious organism requiring the addition of serum or blood to the culture media in order to grow. A selective medium such as modified Thayer-Martin or GCLect should be used for primary isolation, especially from sites that may be contaminated with normal flora. Collection and processing of specimens must be done under optimal conditions, because this organism is sensitive to drying and low temperatures.

An important characteristic of Neisseria gonorrhoeae or the infection it produces is A. A Gram stain of the organism reveals gram-negative bacilli. B. Asymptomatic infections are common in females. C. Produces disease in humans and domestic animals D. The bacteria survive long periods outside the host's body.

B. Neisseria gonorrhoeae is a primary pathogen of the urogenital tract. It is an important cause of sexually transmitted diseases. Surface structures such as pili aid in attachment to mucosal epithelial cells and invasion of submucosa to produce infection.

Reptiles kept as pets are sometimes associated with the transmission of A. Campylobacter B. Helicobacter C. Salmonella D. Vibrio

C. Exotic pets such as iguanas, snakes, and turtles are known to carry Salmonella. Young children who do not practice good handwashing after touching family pets are particularly at risk for infection. Natural medicinal products made from snakes or other animals known to carry Salmonella have been implicated in cases of salmonellosis.

Which microorganism will grow only on culture media supplemented with either cysteine or cystine? A. Actinobacillus lignieresii B. Bartonella bacilliformis C. Francisella tularensis D. Kingella kingae

C. Francisella tularensis requires cysteine or cystine for growth. Glucose-cysteine with thiamine and cystine heart media are commercially available for suspected cases of tularemia. They both require the addition of 5% sheep or rabbit blood. Buffered charcoal yeast extract also supports the growth of F. tularensis, a medium generally used by clinical laboratories for the cultivation of Legionella spp.

Acinetobacter baumannii is characteristically A. Motile B. Oxidase positive C. Sensitive to penicillin D. Able to grow on MacConkey agar

D. Acinetobacter baumannii is not able to reduce nitrate. This species will oxidize but not ferment glucose. Acinetobacter spp. are able to grow on MacConkey agar, and they are oxidase negative, nonmotile, and characteristically resistant to penicillin.

Identify the fermentative agent that may infect reptiles and fish as well as humans when they are exposed to contaminated soil or water. A. Aeromonas B. Chromobacterium C. Chryseobacterium D. Enterobacter

A. Aeromonas spp. are found in bodies of fresh water and salt water that can be flowing or stagnant and contaminated with sewage. These organisms are known as one of the animal pathogens that cause "red leg disease" in frogs. The largest number of human cases occurs between May and November and seems to be highly associated with exposure to water or soil.

Shigella sonnet is differentiated from other Shigella sp. by A. A positive ONPG B. Its positive phenylalanine deaminase reaction C. Its negative oxidase reaction D. Its ability to demonstrate motility at 22°C

A. Shigella sonnet is a group D Shigella and is characterized by its ability to ferment lactose. S. sonnei is ONPG positive but is a delayed lactose fermenter. This is the most commonly isolated species of Shigella in the U.S. The genus Shigella is characterized biochemically by being negative for citrate, urease, motility, and lysine decarboxylation.

Which of the following non-lactose fermenting organisms does not produce fluorescein? A. Pseudomonas alcaligenes B. Pseudomonas aeruginosa C. Pseudomonas fluorescens D. Pseudomonas putida

A. The water-diffusible yellow pigment fluorescein (pyoverdin) is produced by members of the Pseudomonas fluorescent group, which includes Pseudomonas aeruginosa, P. fluorescens, and P. putida. The production of pyoverdin can be detected when a culture of the organism is exposed to a short-wavelength, ultraviolet light source. The production of fluorescent pigments is dependent upon nutritional factors; therefore, special media, such as cetrimide, should be used when trying to detect the pigment. Cationic salts such as magnesium sulfate intensify luminescence.

Salmonella Typhi exhibits a characteristic biochemical pattern, which differentiates it from the other salmonellae. Which of the following is not characteristic of S. Typhi? A. Large amounts of H2S are produced in TSI agar. B. Agglutination in Vi grouping serum C. Lysine decarboxylase positive D. Citrate negative

A. Unlike other salmonellae, Salmonella Typhi produces only a small amount of hydrogen sulfide, produces no gas from glucose, is citrate negative, and possesses a capsular antigen (Vi). Identification of Salmonella Typhi, the etiologic agent of typhoid fever, may be delayed if laboratory professionals do not have a good appreciation of its atypical characteristics. It is also important to note that the bacilli appear in the patient's circulatory system several days before a stool culture will be positive.

Yersinia pestis is characteristically A. Urease negative B. Hydrogen sulfide positive C. Motile at 20-25°C D. Oxidase positive

A. Yersinia pestis is the causative agent of plague. The organism is endemic in rodents and is transmitted to humans by the rat flea. This oxidase-negative organism, unlike other Yersinia spp., is nonmotile at 20-25°C. It is also negative for tLS and urease.

Neisseria lactamica closely resembles Neisseria meningitidis but can be differentiated from it by its ability to metabolize A. Maltose B. Lactose C. Glucose D. Sucrose

B. Neisseria lactamica is part of the normal nasopharyngeal flora of humans. In the laboratory this agent may be mistakenly identified as Neisseria meningitidis, an organism of significant pathogenicity. Differentiation of these two species is easily accomplished by demonstrating the fermentation of lactose or an ONPG (o-nitrophenyl-beta-galactopyranoside) positive test.

A number of vacationers who have traveled outside the U.S. have had their vacations interrupted by a case of "traveler's diarrhea," which is commonly associated with which etiologic agent? A. Aeromonas hydrophila B. Escherichia coli C. Proteus mirabilis D. Vibrio parahemolyticus

B. Traveler's diarrhea is caused by strains of toxin-producing invasive or enteropathogenic Escherichia coli. Enterotoxigenic E. coli can produce one or two exotoxins: one is heat stable and one is heat labile. Contaminated food products and water in foreign countries seem to be the major vehicle for human infection with these agents.

Yersinia pseudotuberculosis is known to manifest commonly as which of the following clinical conditions? A. Epiglottitis B. Hepatitis C. Mesenteric lymphadenitis D. Pseudomembranous colitis

C. Mesenteric lymphadenitis is one of the common manifestations of human Yersinia pseudotuberculosis infections. Symptoms produced by this agent closely resemble those of acute appendicitis. This gram-negative coccobacillus grows well on routine culture media and has an optimal growth temperature of 25-30°C.

Cefsulodin-irgasan-novobiocin (CIN) agar is recommended for the recovery of A. Brucella suis B. Cardiobacterium hominis C. Rhodococcus equi D. Yersinia enterocolitica

D. Cefsulodin-irgasan-novobiocin (CIN) agar is recommended for the primary isolation of Yersinia and Aeromonas. Y. enterocolitic produces "bull's-eye" colonies at 48 hours; colonies show a dark red center surrounded by a translucent border. This is a selective and differential agar that supresses the growth of normal fecal flora and differentiates colonies of Y. enterocolitica.

An unheated suspension of Salmonella Typhi typically produces agglutination of Vi antisera. After heating the same suspension, agglutination will occur in which grouping sera? A. A B. B C. C1 D. D

D. Organisms biochemically resembling Salmonella are typically tested using a polyvalent antiserum composed of antibodies against the commonly isolated strains, including antisera against the Vi antigen. The Vi antigen is a heat-labile capsular antigen associated with Salmonella Typhi. After heating a Salmonella Typhi suspension, the Vi antigen has been removed, and the organism can now react with the somatic grouping antisera. Salmonella Typhi demonstrates a positive agglutination reaction in D-grouping sera

A fastidious gram-negative bacillus was isolated from a case of periodontal disease, which upon darkfield examination was noted to have gliding motility. The most likely identification of this etiologic agent would be A. Capnocytophaga B. Chromobacterium C. Kingella D. Plesiomonas

A. Capnocytophaga spp. are fermentative gram-negative bacteria that inhabit the oral cavity of humans. These organisms have been identified as a cause of disease in the oral cavity, and in compromised hosts they have been implicated in systemic disease isolated from cerebrospinal fluid, pleural fluid, and pulmonary secretions. The gliding motility is best observed during the log phase of growth and can be demonstrated by darkfield microscopy and on sheep blood agar by the production of concentrically spreading growth around primary colonies.

The sexually acquired disease characterized by genital ulcers and tender inguinal lymphadenopathy, which is caused by a small, gram-negative bacillus, is known as A. Chancroid B. Bacterial vaginosis C. Syphilis D. Trachoma

A. Chancroid or soft chancre is caused by Haemophilus ducreyi, a small, gram negative coccobacillus. Painful genital lesions and painful swelling of the inguinal lymph nodes characterize the disease. The incubation period following contact with an infected person ranges from 1 to 5 days, after which the patient notes the painful, round, nonindurated primary lesion on the external genitalia. Signs of regional lymphadenitis appear in about one-half of the cases a few days after the appearance of the primary lesion.

Which one of the following organisms would produce a yellow slant and a yellow butt on TSI agar after incubating 18 hours? A. Escherichia coli B. Proteus mirabilis C. Salmonella Typhimurium D. Shigella sonnei

A. E. coli produces an acid over acid (A/A) reaction on TSI agar that indicates that glucose and either lactose or sucrose or both have been fermented. Bacteria that ferment lactose or sucrose produce large amounts of acid in the medium. The enteric pathogens Salmonella and Shigella can be ruled out when such a reaction is observed, because they are generally not able to use either lactose or sucrose within 18 hours.

On Gram stain, a morphology that resembles "seagull wings" is most characteristic of A. Campylobacter jejuni B. Neisseria gonorrhoeae C. Plesiomonas shigelloides D. Yersinia pseudotuberculosis

A. Fresh isolates of Campylobacter jejuni on Gram stain characteristically reveal a "gull-wing" appearance. These gram-negative bacilli are motile with a typical darting pattern on wet mounts. They stain poorly using the Gram stain method, and it is recommended that carbolfuchsin or basic fuchsin be substituted for the counterstain safranin.

A causative agent of the form of conjunctivitis known as pinkeye is A. Haemophilus aegyptius B. Moraxella lacunata C. Chlamydia trachomatis D. Klebsiella ozaenae

A. Haemophilus aegyptius is the causative agent of "pinkeye." This form of conjunctivitis is highly contagious and is frequently seen in children attending daycare centers. The agent is an aerobic gram-negative bacillus that is nonmotile and requires both hemin (X factor) and nicotine adenine dinucleotide (NAD, V factor) for growth.

The single species in the genus Hafiiia is A. alvei B. gergoviae C. ruckeri D. tarda

A. Hafnia is a member of the family Enterobacteriaceae. Hafnia alvei is the only species in the genus. The characteristics of this organism are positive motility and lysine, ornithine, ONPG, and KCN reactions.

Acinetobacter baumannii A. Requires cysteine B. Is oxidase negative C. Ferments glucose D. Does not grow on MacConkey agar

B. Acinetobacter spp. are opportunistic pathogens for humans and are important causes of nosocomial infections. They are oxidase negative and will grow on most laboratory media, including MacConkey agar. Acinetobacter spp. are nonfermenters, but A. baumannii can form pink to purple colonies on MaConkey agar that can be mistaken for lactose fermentation. Many strains of A. baumannii will oxidize glucose.

Blood cultures are recommended for the recovery of which of the following microorganisms? A. Acinetobacter baurnannii B. Brucella canis C. Chlamydia trachomatis D. Yersinia enterocolitica

B. Cultures of blood and bone marrow are the recommended specimens for the isolation of Brucella spp. Inoculation of a blood culture bottle for a continuous monitoring system is the most senstitive recovery method. The lysis-centrifugation method (Isolator®, Wampole Laboratories) is more sensitive than a biphasic culture bottle.

A culture of a decubitus ulcer grew a gram-negative facultative bacillus. On TSI it produced an acid slant, acid butt, and gas. Test reactions in other media were as follows: Citrate :negative Indole :positive Urease: negative ONPG: positive Voges-Proskauer: negative The organism was identified as A. Enterobacter cloacae B. Escherichia coli C. Citrobacter (diversus) koseri D. Providencia stuartii

B. Decubitus ulcers frequently contain normal intestinal flora. The biochemical results are characteristic of Escherichia coli. E. coli is associated with a variety of diseases; it is the predominant organism associated with cases of neonatal meningitis, specticemia, cystitis, appendicitis, and endocarditis

Lack of motility is characteristic of A. Enterobacter cloacae B. Klebsiella oxytoca C. Morganella morganii D. Providencia stuartii

B. Motility can be important in the identification of microorganisms. Of the Enterobacteriaceae, the genera Klebsiella and Shigella are characteristically nonmotile, as is Tatumella. Motility of the Enterobacteriaceae can normally be detected by the use of a semisolid motility medium, which is grossly observed for the determination of motility. The hanging-drop method is perhaps the most accurate means of detecting motility of nonfermentative microorganisms.

Which of the following statements is not true of Brucella? A. Infection may occur via abrasions of the oral mucosa, conjunctiva, and genitals. B. They are fastidious and require supplemented media for isolation. C. The risk of accidental laboratory infection is no greater than with any other organism. D. Phage and dye sensitivity tests are used for identification to the species level.

C. Brucella spp. are harzardous, especially in aerosol-generating procedures. It is important for the laboratory to be notified whenever brucellosis is suspected. Most laboratories send isolates to a reference laboratory for confirmation or definitive identification because they lack specialized media and containment facilities.

Campylobacter jejuni is A. Nonmotile B. Oxidase negative C. Hippurate hydrolysis positive D. A straight gram-negative bacillus

C. Campylobacter jejuni are small, curved, motile gram-negative rods that are hippurate hydrolysis positive. They are found in the gastrointestinal tract of a variety of animals. Campy agar is used for isolation from stool and is incubated at 42°C under microaerophilic conditions (10% CO2, 5% O2 with balance N2) for 72 hours.

Cardiobacterium hominis, an inhabitant of the upper respiratory tract of humans, has been recovered as the etiologic agent from cases of endocarditis. An identifying characteristic of the organism is A. Positive oxidase B. Positive catalase C. Indole negative D. Inability to grow on sheep blood agar

C. Cardiobacterium hominis is a rare pathogen that is recovered predominantly from cases of endocarditis. It is characterized as a fermentative, gram-negative bacillus that is nonmotile, catalase negative, oxidase positive, and weakly indole positive. C. hominis will grow on sheep blood agar, but growth is enhanced by the addition of yeast extract to media.

Which of the following species of Pasteurella is associated with human infections following cat bites? A. P. avium B. P. canis C. P. multocida D. P. stomatis

C. In the genus Pasteurella, P. multocida is the species commonly recovered in clinical specimens. This gram-negative coccobacillus is a normal inhabitant of the oral cavity of domestic animals. Humans most often become infected from a bite or scratch of a cat or dog, which produces a rapidly progressing, painful, suppurative wound infection. Penicillin is an effective drug for the treatment of Pasteurella infections

A gram-negative bacillus was recovered from the urine of a child with a history of recurrent urinary tract infections. The organism was oxidase negative, lactose negative, urease positive, and motile. The most likely identification of this agent would be A. Escherichia coli B. Klebsiella pneumoniae C. Proteus mirabilis D. Pseudomonas aeruginosa

C. Proteus mirabilis is commonly associated with urinary tract infections as well as infections in other parts of the body. It is a motile organism that characteristically swarms across the surface of sheep blood agar plates. Members of the genus Proteus are characteristically rapidly urea positive, lactose negative, and phenylalanine deaminase positive.

Which of the following is the optimal clinical specimen for the recovery of Legionella pneumophila ? A. Stool B. Blood C. Bronchial washings D. Nasopharyngeal swab

C. Tissue samples from the lower respiratory tract (lung biopsy) have the greatest yield of positive cultres for Legionella pneumophila. However, these specimens require invasive procedures and are not commonly performed. Cultures of lower respiratory tract specimens, such as bronchial wash and expectorated sputum, are appropriate for the isolation of L. pneumophila. The bacteria are seldom recovered from blood specimens.

The species of Vibrio closely associated with rapidly progressing wound infections seen in patients with underlying liver disease is A. V. alginolyticus B. V. cholerae C. V. vulnificus D. V. parahaemolyticus

C. Vibrio vulnificus is implicated in wound infections and septicemia. The organism is found in brackish or salt water. Ingestion of contaminated water or seafood is the typical mode of transmission. Wound infections are associated with contamination at the site with organisms in water.

A negative citrate reaction is characteristic of A. Citrobacterfreundii B. Enterobacteraerogenes C. Serratia marcescens D. Shigella boydii

D. Citrate utilization is a common test used for the differentiation of members of the family Enterobacteriaceae. Both Escherichia coli and Shigella boydii are incapable of using citrate as the sole source of carbon as an energy source. Organisms such as Citrobacter freundii, Enterobacter aerogenes, and Serratia marcescens are able to grow on citrate agar and produce a color change from green to blue in the medium. Many Enterobacteriaceae that are Voges-Proskauer positive are also citrate positive.

An organism occasionally misidentified as an enteric pathogen because it produces a large amount of H2S is A. Burkholderia cepacia B. Burkholderia pseudomallei C. Pseudomonas putida D. Shewanella putrefaciens

D. Screening procedures for the recovery of the enteric pathogen Salmonella rely heavily on differential media, which indicate lactose fermentation and the production of H2S. Isolates of Shewanella putrefaciens recovered from stool samples on a medium such as Hektoen enteric agar would resemble Salmonella in that the organism is not able to ferment lactose and does produce a significant amount of H2S. However, unlike Salmonella, some strains of S. putrefaciens will produce acid from sucrose, forming yellow colonies on Hektoen enteric agar.

The method of serogrouping Shigella used in the clinical laboratory is based on A. Bacteriocins B. H antigens C. K antigens D. O antigens

D. The most commonly used method for serogrouping Shigella is based on the somatic oligosaccharide or O antigens. The O antigens are also used to serogroup Escherichia coli and Salmonella. Because Shigella spp. are nonmotile, the H or flagella antigens cannot be used; however, H antigens are used for E. coli and Salmonella. The capsule (K) antigens are used to serogroup Klebsiella pneumoniae.

Serratia spp. are unique in the family Enterobacteriaceae because of their ability to produce extracellular hydrolytic enzymes. Which of the following is not produced by Serratia species? A. DNase B. Gelatinase C. Lipase D. NADase

D. The production of DNase, lipase, and gelatinase differentiates the genus Serratia from other Enterobacteriaceae. Serratia spp., especially S. marcescens, have a close association with nosocomial infections. Serratia can produce severe infections such as septicemia and meningitis and are frequently difficult to eradicate because of the characteristic antimicrobial-resistant strains found in the hospital environment.

Explosive watery diarrhea with severe abdominal pain after eating raw shellfish is most characteristic of infection caused by A. Campylobacter jejuni B. Helicobacter pylori C. Shigella dysenteriae D. Vibrio parahemolyticus

D. Vibrio parahemolyticus is found in brackish or salt water. The mode of transmission is the ingestion of contaminated water or seafood. V. parahemolyticus is halophilic.

A positive DNase would be seen with A. Escherichia coli B. Klebsiella oxytoca C. Proteus mirabilis D. Serratia marcescens

D. When streaked on DNase test medium, colonies of Staphylococcus aureus and Serratia marcescens will demonstrate a positive reaction for DNase activity. Inoculated plates are incubated 18 to 24 hours, after which the plates are flooded with a 0.1% solution of HC1. DNaseproducing organisms are differentiated by the development of a clear zone in the agar around the colonies.