Analytic Procedures for Bacteriology-Blood and Bone Marrow

The red ring at the top of the media in this tube indicates a positive indole reaction. The precursor substance in the medium from which the indole is produced is:

tryptophan

GN Broth (Gram-Negative Broth)

used for the recovery of gastrointestinal pathogens from stool specimens. GN Broth is used for the recovery of Salmonella and Shigella species.

Bismuth Sulfite Broth

used to isolate Salmonella species. It uses glucose as a primary source of carbon. BLBG and bismuth stop gram-positive growth. Bismuth sulfite agar tests the ability to use ferrous sulfate and convert it to hydrogen sulfide.

BacT/ALERT

uses colorimetric sensor methodology located at the bottom of the blood culture bottle to identify the growth of bacterial organisms. As CO2 is produced, the CO2 will dissolve in the water within the sensor and free hydrogen ions will be generated. As a result of hydrogen ion production, a color change will occur from blue to light green to yellow as the pH decreases. The instrument will read this color change and alert the microbiologist that a blood culture is positive.

CNA agar

will inhibit gram negative organism, staphylococci, Bacillus spp., and coryneforms, making it useful for specimens with mixed flora. Therefore, it is a selective type of agar.

Moraxella species

normal flora of the respiratory tract. Commonly causes respiratory, eye, ear, and sinus infections. Are large, pink to brown colonies in color and produce a hockey puck-type colony that easily glides across the surface of chocolate media.

Kingella kingae

predilection for causing infections of the bones and joints, particularly of young children, and is associated with juvenile osteomyelitis.

The organism Acinetobacter baumannii is known to have caused which of the following outbreaks?

Afghanistan and Iraq U.S. solider outbreak, Acinetobacter baumannii is nicknamed Iraqibacter because it is commonly isolated from soldiers injured in Afghanistan and Iraq.

Which of the following is only observed in Salmonella infections and not in Shigella infections?

Animals serve as a reservoir of infection. Shigella infections are only exhibited in humans while Salmonella infections are found in many animals, in addition to humans. Both types of infections have diarrhea as the major symptom. Endotoxin is produced by all gram-negative bacteria, and exotoxin is only produced by Shigella.

Which one of the following pathogenic anaerobic bacteria is MOST frequently isolated in clinical laboratories?

Bacteroides fragilis. Bacteroides is a predominant anaerobic bacterium of the human colon, represent the major group of obligate anaerobes involved in human infections and are known to cause either bacteremia or localized abscesses. Of the numerous species of Bacteroides, Bacteroides fragilis is the most frequent clinical isolate.

A cancer patient was admitted to the hospital with fever, tachycardia, and a drop in blood pressure. Due to the patient being treated for cancer, her chemotherapy had been administrated through an intravenous catheter. To rule out a catheter-related infection, the physician ordered two sets of blood cultures with one set being collected from the catheter site and the second set being collected by venipuncture. After 48 hours, the patient had positive blood cultures that grew Staphylococcus epidermidis. How will the physician know if the Staphylococcus epidermidis present is due to an infected catheter or is a contaminant?

Both blood culture sets (catheter and venipuncture) will be positive

capable of producing an extremely potent, lethal neurotoxin?

Botulinum toxin is an extremely potent and deadly neurotoxin produced by Clostridium botulinum and a few other Botulinum species. Foodborne botulism is caused by germination of spores in improperly preserved food, with subsequent ingestion of the toxin.

A patient was admitted to the hospital for fever, chills, weight loss, headaches, and fatigue. The patient mentioned that he had cut his hand while hunting wild boar a couple of weeks ago. Blood cultures were received in the microbiology laboratory and several days later a bone marrow specimen on the patient was received. The blood culture was positive after 5 days and the bone marrow grew a small, convex, smooth colony after 48 hours on sheep blood and chocolate agar. A gram stain was performed and demonstrated small Gram-negative coccobacilli organisms. Which of the following organisms is the cause of infection for this patient?

Brucella suis, commonly found in the wild boar population. Brucella species are facultative, intracellular organisms that can live in neutrophils, monocytes, and macrophages. As a result, can circulate throughout the bloodstream and invade other organs such as the spleen, liver, and bone marrow. People who have Brucella infections can be asymptomatic or symptomatic and those who are asymptomatic have a delay in medical treatment. This delay can result in relapsing brucellosis and possibly further complications of the disease. Complications that can occur are arthritis, spondylitis, and endocarditis.

A technologist subcultures a positive blood culture and notes the following characteristics on the isolated colonies displayed in the image below: - Growth of non-hemolytic colonies with a ground-glass appearance, displaying a "Medusa Head", as indicated by the arrows - Gram stain reveals a large, gram-positive rod with central and subterminal spores that do NOT swell the cells - Catalase positive - Non-motile What would be the MOST likely conclusion and action?

Cannot rule out Bacillus anthracis, refer isolate to your Laboratory Response Network (LRN) Reference Laboratory.

Beta hemolytic colonies grew from the blood culture bottle after 18 hours of incubation (see image). If the gram stain shows gram-positive cocci, which of the following tests would be helpful with making a preliminary identification? A. Catalase B. Regrow on CNA plate C. Serological testing D. Vancomycin susceptibility

Catalase. Streptococci are catalase negative while the Staphylococci are catalase positive, which is helpful in establishing a genus identification.

The disk to test for methicillin-resistant staphylococci

Cefoxitin. Although penicillinase-resistant penicillins, such as methicillin, nafcillin, and oxacillin, are the mainstay of anti-staphylococcal therapy, resistance is common.

An uncommon laboratory isolate, the colonies on blood agar, as seen in the top upper frame of the composite image were cultured from the throat swab of a 10 year old girl presenting with a red throat and mucosal pseudomembrane. These tiny gray-white, non hemolytic colonies are non-descriptive. Distinctive are the black pigmented colonies as observed on Tinsdale agar (lower image in the top composite photograph). Illustrated in the lower composite photomicrograph (upper image) are slender gram positive bacilli. Bacilli with meta-chromatic granules are observed in a methylene blue stained microscopic mount (lower image).

Corynebacterium diphtheriae

Francisella tularensis requires for optimal growth?

Cysteine for optimal growth, grows best on CHOC or other media containing cysteine. However, colonies may not be visible for 3-4 days. F. tularensis does not grow on MAC or EMB. Positive tests for F. tularensis include catalase and beta-lactamase. Negative results include oxidase, X and V factor requirements, and urease.

Arcanobacterium haemolyticum colonies on blood agar are also small and beta-hemolytic also and are catalase-negative.

Distinctive is a reverse CAMP reaction in which the zones of hemolysis are in a cup-shaped downward projection rather than extending upward. Motility and esculin reactions are negative.

Which of the following Enterococcus species is motile, mannitol positive, pyruvate negative, and is a rare cause of clinical infections?

Enterococcus casseliflavus is rarely isolated and is the only Enterococcus species other than Enterococcus gallinarum that is motile. It is also mannitol positive

The upper image is a photomicrograph of a Gram stain prepared from a positive blood culture obtained from a 68 year old female with an indwelling urinary bladder catheter. Smooth, gray, faintly beta hemolytic colonies were recovered in subcultures of the positive bottle. The tubes shown in the lower photograph are: - an esculin slant (left) displaying intense brown coloration - a 6.5% sodium chloride broth (right) showing cloudy growth The most likely identification is:

Enterococcus faecalis, The Gram stain is gram-positive cocci in pairs and short chains consistent with Enterococcus species. The hydrolysis of esculin and ability to grow in 6.5% sodium chloride are characteristics consistent with that species. Enterococcus faecalis can be alpha, beta, or gamma hemolytic on sheep blood agar.

An autopsy of a 1-year-old female admitted to the emergency room 4 hours prior to her death revealed Waterhouse-Friderichsen syndrome. Blood and nasopharyngeal cultures taken prior to her death should reveal an oxidase-positive, Gram-negative diplococcus with the following biochemical reactions:

Glucose positive, Maltose positive, Lactose negative and Sucrose negative is the correct answer since Neisseria meningitidis causes Waterhouse-Friderichsen syndrome and it is positive only for glucose and maltose.

Which of the following statements reflect accurate identifications of Enterococcus species?

Gram positive cocci in pairs or chains, catalase negative, esculin positive, PYR positive, vancomycin intermediate, motile, yellow pigment: Enterococcus casseliflavus. Both E. gallinarum and E. casseliflavus are motile. In addition, E. casseliflavus possesses a yellow pigment.

Blood culture bottles utilized in continuous monitoring systems, such as the BacTec, use resins or charcoal to do which of the following?

Inactivate and absorb out antimicrobial agents. Resins and charcoal are able to absorb out and inactivate antimicrobial agents, which will enhance the recovery of microorganisms. However, when reading Gram stains from bottles that use charcoal, caution should be used as the charcoal can be misinterpreted as Gram-positive cocci.

chemical products resulting from the deamination of the amino acid tryptophan, under the action of the enzyme tryptophanase, produced by indole-positive bacterial species.

Indole, along with pyruvic acid and ammonia

Observed in the top photographs are colonies growing on blood agar after 24 hours incubation, obtained from a positive blood culture. The colonies are tiny and surrounded by narrow zones of beta hemolysis. The initial presumptive identification was that of a Streptococcus and a CAMP test was set up. A follow-up Gram stain (middle image) revealed Gram-positive bacilli in loose clusters rather than cocci. The lower image demonstrates a rectangular zone of hemolysis in the CAMP test, compared to the arrow-head shape of a control Streptococcus. From these observations, select the most likely presumptive identification of this isolate.

Listeria monocytogenes. Colonies on blood agar are initially small, gray to yellow-white, surrounded by narrow zones of beta hemolysis, and look almost exactly like Streptococcus agalactiae. Characteristic of L. monocytogenes is a positive CAMP reaction with a rectangular zone of beta hemolysis in contrast to the arrow-head shape produced by Streptococcus agalactiae.

A culture from a sputum specimen grew a mucoid, lactose fermenting organism. Biochemical testing on this isolate gave the following key reactions: VP: positive; Indole: negative; Urea: 1+, Motility: nonmotile, Citrate: positive. What is the most likely organism given the site of isolation and biochemical reactions?

Klebsiella pneumoniae. Biochemical test results such as VP-positive, Urea-1+, Motility- nonmotile, citrate- positive, and indole are helpful in separating Klebsiella from Escherichia coli in the clinical microbiology laboratory.

Bacillus cereus

Large, box-car-shaped gram-positive bacilli are observed in microscopic mounts that lie singly or in short chains. Central and sub-terminal ellipsoidal spores are also distinctive. colonies on blood agar are large, flat with a matte appearance, spreading, with gray-white round surfaces with fimbriated edges. Beta hemolysis is observed.

CAMP Test for the identification of Listeria monocytogenes

Listeria monocytogenes is streaked at right angle to the streak of beta-hemolytic Staphylococcus aureus on sheep blood agar plate. Then incubate the plate in ambient air at 37 degree Celsius for 24 hours. Positive CAMP: Enhanced zone of beta-hemolysis and a smaller less obvious rectangular zone of hemolysis.

Which of the following instruments is used for continuous monitoring of mycobacterial growth?

MGIT 960, a fully automated system to detect growth of mycobacteria. This instrument uses a MGIT (modified Middlebrook 7H9 broth) that incorporates a fluorescence quenching based oxygen sensor for detection. If a mycobacterium organism is growing, the oxygen will be utilized, and the concentration will decrease allowing the sensor to fluoresce.

Which of the following organisms is an aerobic, gram-negative diplococcus that does not ferment sugars and is DNAse positive?

Moraxella catarrhalis is a common laboratory isolate that is distinguished from other gram-negative diplococci, including Neisseria species and Kingella species, by not fermenting any of the commonly tested carbohydrates and is DNAse positive. It is also aerobic.

The most common organism that causes septic arthritis in patients under 30 years of age is:

Neisseria gonorrhoeae. Septic arthritis in patients under the age of 30 is most commonly associated with acute gonorrhea caused by infections with Neisseria gonorrhoeae. Gonococci may invade the bloodstream, resulting in disseminated gonococcal infection (DGI). Complications of DGI include permanent joint damage, endocarditis, and rarely meningitis.

Illustrated in the image to the right is a tube of tryptophane agar with a positive indole reaction, as seen by the red ring at the top of the medium. It is necessary to use xylene extraction and Ehrlich's reagent rather than the conventional Kovac's reagent when detecting indole production by which of the following organisms?

Porphyromonas asaccharolytica.. Ehrlich's reagent is formulated in ethyl alcohol rather than the isoamyl alcohol contained in Kovac's reagent. For bacterial species that are extremely weak producers of indole, such as Porphyromonas asaccharolytica, the indole in the medium must first be extracted with xylene or a comparable organic compound and then reacted with the more sensitive Ehrlich's reagent.

Specimen handling from patients with symptoms consistent with tularemia requires work in a biological safety cabinet. Although PCR may confirm infection with Francisella tularensis, the following culture characteristics and tests aid in presumptive identification:

No growth on MAC, slow growth on CHOC; oxidase negative, positive catalase and ß-lactamase.

Systemic inflammatory response syndrome (SIRS)

Occurs due to a dysregulation of the immune system due to infections. If a person has an increase in two or more of the following, then they are considered to be having a SIRS response: Increase in body temperature, heart rate, respiration, and/or white blood cell count.

Which Enterobacteriaceae are non-lactose fermenters on MacConkey (MAC) agar, have green colonies with black centers on Hektoen enteric (HE) agar, and on xylose-lysine-deoxycholate (XLD) agar will have red colonies with black centers?

Salmonella spp. are non-lactose fermenters on MAC, have green colonies with black centers on HE, and red colonies with black centers on XLD.

A tech is interpreting a urine culture with a source of suprapubic aspiration. There is one colony of Staphylococcus epidermidis present on the blood agar which was streaked with a 0.01 loop. What should the tech do next?

Report and provide a sensitivity for the S. epidermidis.

Acinetobacter species

non-lactose fermenter and grows easily on sheep blood, chocolate, and MacConkey agar. Acinetobacter species are gram-negative coccobacilli and can often be mistaken for Neisseria species.

Salmonella and Shigella will appear as non-lactose fermenting colonies on MacConkey agar and highly selective media, such as Hektoen enteric (HE). HE medium also includes ferric salts which will show black centers in the colonies if hydrogen sulfide gas is produced.

Salmonella will grow as blue-green colonies (a non-lactose fermenter) with black centers on HE and Shigella will produce colonies without black centers on blue-green HE.

Which of the following is characterized by hypotension due to systemic infection that does not respond to fluid resuscitation (an attempt to replenish body fluid)?

Septic shock. Severe sepsis progresses to septic shock if the hypotension caused by systemic infection does not respond to fluid resuscitation. Septic shock results from the by-products of growing organisms acting on the host body and the host body reacting to the by-products. Gram-negative rods cause the most serious conditions of septic shock. Disseminated intravascular coagulation (DIC) is a complication of septic shock.

The recovery of Mycoplasma hominis from the genital tract of females has been associated with all of the following clinical syndromes

Several recently published studies indicate that the presence of M. hominis in the genital tract of pregnant women may result in premature rupture of membranes, delivery of low birth weight infants, and prematurity

Erysipelothrix rhusiopathiae

Small and gray-white on blood agar. Catalase is negative. The CAMP test is negative. To confirm the identification, the organism is H2S positive, Voges-Proskauer negative, and creates a test-tube brush-like appearance in a gelatin stab.

Bacillus anthracis

commonly encountered through direct contact with sheep, goats, horses, and cattle. Bacillus anthracis infections occur through direct contact with wool or hair of infected animals, inhalation of spores, and ingestion of contaminated meat. In addition, Bacillus anthracis are large Gram-positive rods that grow within 24 hours on sheep blood and chocolate agar.

Purulent material is obtained from a carbuncle and submitted for bacterial culture. Many Gram-positive cocci and white blood cells were seen on a direct smear (top right image). Colonies on blood agar are, smooth and gold/yellow surrounded by a narrow zone of beta hemolysis (top left image). Coagulase tests are shown in the bottom images. The slide coagulase test is negative, but the tube coagulase test is positive. The probable presumptive identification is:

Staphylococcus aureus. The smooth, golden-yellow colonies on blood agar ("aureus") and beta hemolysis, and the grape-like clustering of Gram positive cocci on gram stain are distinctive for a presumptive identification of Staphylococcus aureus. The identification is confirmed by the positive tube coagulase test.

Illustrated in the top photograph are alpha-hemolytic, entire, gray-white convex colonies that are of a bacterial species that was found to be susceptible to vancomycin. In the lower photomicrograph, gram-positive cocci arranged in chains and in loose clusters that are not species distinctive are seen. Select the bacterial species that are uncommonly vancomycin-resistant.

Streptococcus species. Although isolated strains of alpha-hemolytic streptococcus may be vancomycin-resistant, most are susceptible.

A budding yeast with pseudohyphae and clusters of gram-positive staphylococci were observed in a Gram stain smear prepared from a positive blood culture. What is the MOST likely source of the infection?

The most likely source of the infection is an indwelling catheter. The budding yeasts with pseudohyphae are indicative of Candida species. The staphylococci seen here are in distinct grape-like clusters, most consistent with S. aureus. Either of these species could account for any one of the clinical conditions indicated in this exercise; however, the most likely common source for both organisms would be an indwelling catheter. Catheters are vulnerable to colonization with organisms found on the patient's skin. Both S. aureus and C. albicans have been recovered as normal skin biota.

All HACEK members are known to cause

endocarditis

This photograph is of an isolate from a stool culture on a 4-year-old child with gastroenteritis. The medium contains cefsulodin, irgasan, novobiocin, bile salts, mannitol, neutral red, and crystal violet. Further identification tests will most likely identify this isolate as:

Yersinia enterocolytica. Cefsulodin-irgasan-novobiocin (CIN) agar is selective for Y. enterocolytica. It forms red-centered colonies because the mannitol is fermented causing a change in pH of the neutral red indicator.

Streptococcus agalactiae

can also cause bacterial meningitis, in neonates (less than one-month-old) and infants (1 to 23 months of age), and Listeria monocytogenes in infants and in adults older than 65 years of age.

Cardiobacterium hominis

infects the aortic valve more frequently than other HACEK organisms.

Aminoglycosides and tetracyclines

interfere with the 30S ribosomal subunit (protein synthesis inhibitors).

Staphylococcus saprophyticus

involved in urinary tract infections, particularly in middle-aged females and can grow in 6.5% sodium chloride; however, it appears as Gram positive cocci in clusters rather than in chains and does not hydrolyze esculin.

Thioglycollate broth

is an enrichment medium for anaerobes, aerobes, and facultative organisms.

Treponema pallidum

is the agent of venereal syphilis if left untreated in the primary stage can develop secondary and even tertiary stages with systemic symptoms. Organs involved in these late stages include the eyes, ears, liver, and central nervous system.

Chlamydia trachomatis

is the most common sexually transmitted bacterial pathogen and a major cause of pelvic inflammatory disease (PID), ectopic pregnancy, and infertility (serovars D-K). Some serovars are responsible for endemic trachoma worldwide (A, B, Ba, and C), or lymphogranuloma venereum (L1, L2, L2a, and L3).

Aggregatibacter (formerly Actinobacillus) actinomycetemcomitans

member of the normal oral flora and is a major cause of juvenile periodontitis. In these individuals, it can cause destruction of the alveolar bone supporting the teeth.

Prevotella species

most commonly found as normal microbiota of the oral cavity. Prevotella melaninogenica is known to cause oral, pulmonary, skin, and soft tissue infections.

This member of the Enterobacteriaceae was isolated from a stool specimen and gave the following biochemical reactions: TSI: K/A, no gas, no H2S Citrate: Positive Lysine decarboxylase: Negative Ornithine decarboxylase: Positive Indole: Negative This organism agglutinated in Group D Shigella antiserum. All of the above biochemical results are consistent with this identification, EXCEPT? A. TSI B. Citrate C. Lysine D. Indole

Citrate. Shigella species are all citrate negative. The other three results are all consistent with an identification of Shigella sonnei.

Eikenella corrodens is associated with

Clenched fist infection. Eikenella corrodens is a normal inhabitant of the oropharynx. Most infections result of trauma especially human bite wounds or fistfights. Inflammation of the knuckles following fistfights may occur and are known as clenched fist wounds or infections. This is a member of the HACEK group.

Streptococcus pneumoniae

Colonies are large and mucoid indicating the synthesis of capsular polysaccharide. Narrow zones of alpha hemolysis may be observed. More mature colonies may present sunken centers often referred to as "checker pieces". S. pneumonia is also susceptible to optochin. Lancet-shaped Gram positive cocci in pairs ("diplococci").

Staphylococcus epidermidis

Colonies are white, raised, convex colonies and are not hemolytic on blood agar. Catalase-positive and coagulase negative. Sensitive to novobiocin, providing an important test to distinguish it from Staphylococcus saprophyticus, which is coagulase-negative, but novobiocin-resistant.

Reagent added to the incubated media to detect the presence of indole?

P-dimethylaminobenzaldehyde

Sodium polyanethol sulfonate (SPS) with a concentration of 0.025% - 0.05% can be found in blood culture bottles. This additive has anticoagulant, anticomplementary, and antiphagocytic properties.

Inactivates and absorbs out complement, inactivates and absorbs out coagulation factors, and inactivates neutrophils and monocytes.

The purpose of the additive SPS (sodium polyanethol sulfonate) that is in continuous monitoring system blood culture bottles is to

Inactivates and absorbs out complement, inactivates and absorbs out coagulation factors, and inactivates neutrophils and monocytes. SPS is most known for its anticoagulant, anticomplementary, and antiphagocytic properties even though it can interfere with aminoglycoside activity.

Who should a technologist contact if an organism is isolated that cannot be ruled out as a potential agent of bioterrorism?

The Laboratory Response Network (LRN) reference laboratory. The sentinel laboratory should NOT make the decision that a bioterrorism event has occurred, thus should not contact law enforcement or public health officials.

oxidase test

The oxidase test determines the presence of the cytochrome oxidase system that oxidizes reduced cytochrome with molecular oxygen. Helpful in differentiating between the Enterobacteriaceae, which are oxidase negative (except for Plesiomonas spp.), and the pseudomonads, which are oxidase positive. Neisseria spp. are also oxidase-positive.

The Gram stain shown in the image was prepared from a positive anaerobic blood culture bottle after 36 hours incubation. Based on the morphology of the bacterial cells (some with spores, noted by the blue arrows), what is the most likely identification?

The presence of spores rules out Clostridium perfringens, which virtually never produces spores in clinical infections. Lactobacillus rhamnosus is a non-spore-forming, gram-positive bacilli, rarely isolated in blood cultures. Although gram-negative appearing bacilli (over decolorized) are observed, presence of spores eliminates Bacteroides fragilis. By elimination, Clostridium septicum is the correct answer.

The presence of a polysaccharide capsule helps to prevent phagocytosis and protect against the oxidative burst of neutrophil lysosomal granules if phagocytosis does occur.

Bacteria with a polysaccharide capsule have a high level of virulence. The capsule masks the surface receptors on the bacterium which prevents recognition by phagocytic cells.

A 25-year-old motorcyclist incurred superficial and deep penetrating lacerations of his right shoulder when thrown off his speeding vehicle into the ditch. The shoulder became painful and continued to swell over the next 24 hours. The bacterial species shown in the upper image was recovered after 36 hours under anaerobic incubation and the lower image illustrates the microscopic features. What is the most likely identification?

Clostridium perfringens, post-trauma gas gangrene. The double zone of hemolysis seen in the upper image (the blue arrow indicates the inner zone of beta hemolysis, the green arrow the outer faint zone of lecithinase activity) is characteristic of C. perfringens, helping to differentiate this species from C. septicum.

The flat, spreading gray-white colonies with an outer zone of beta hemolysis as observed on the surface of an anaerobic blood agar plate shown in the upper image were recovered from a blood culture of an elderly man leading to a potential diagnosis of cancer of the colon. Observed in the gram stain are short gram-positive bacilli, some with distinctive central and sub-terminal spores. The organism is a lactose fermenter and produces DNAse.

Clostridium septicum, Distinctive, are flat, spreading gray-white colonies with surrounding beta hemolysis. Short varying sized rectangular gram-positive coccobacilli, some of which have distinctive central and sub-terminal spores. Associated with cancer of the colon. Key characteristics are fermentation of glucose and lactose, hydrolysis of gelatin, and production of DNAse.

Streptococcus agalactiae (Group B)

Colonies on blood agar are relatively large, smooth, transparent, and surrounded by a small zone of beta hemolysis. The Group B antigen latex agglutination is positive. S. agalactiae is commonly associated with in-utero and para-natal infections.

This non-hemolytic organism was isolated from the blood culture of a patient. The image shows the organism's reactions in 6.5% NaCl broth and on bile esculin agar. With further testing, this isolate will most likely be identified as:

Enterococcus spp. it is 6.5% NaCl positive (growth with color change from purple to yellow) and bile esculin positive (growth and darkening of the slant).

A 30-year-old Hispanic pregnant female developed fever and signs and symptoms of meningitis following ingestion of cheese sent by relatives in Mexico. The colonies recovered from a positive blood culture are shown in the upper photograph; the microscopic features are in the lower photograph. The most likely identification is:

Listeria monocytogenes and milk and milk products (when unpasteurized) is well known. Pregnant women and immunosuppressed persons are susceptible to infection with L. monocytogenes following ingestion of various contaminated foods, namely milk and milk products, undercooked chicken, turkeys, and other meats and vegetables.

What virulence factor is not inherent to bacterium? a. Presence of a polysaccharide capsule b. Production of a proteolytic enzymes c. Production of opsonins d. Presence of surface membrane attachment receptors

Opsonins are not inherent part of the bacterial cell, nor are they produced by the bacterium. Opsonins are factors present in the host body fluids that actually work to the disadvantage of the bacterium by enhancing their susceptibility to phagocytosis.

Illustrated in the photograph of the blood agar plate are slow-growing colonies after 72 hours incubation that are pink-white, appear dry, and heaped in areas of confluent growth (arrows). Recovered from a tooth abscess of a 14-year-old boy. Gram stain reveals short gram-positive bacilli that characteristically are in a diphtheroidal arrangement. Key characteristics to provide a definitive identification include positive for catalase, nitrate reduction, esculin, and pyrazinamidase. Based on these observations, select the presumptive identification of this isolate?

Rothia dentocariosa, common recovery from infected teeth and gums. This presumptive identification is supported by the heaped colonies with a light pink-white surface. Long, slender non-spore-forming gram-positive bacilli and cocco-bacilli in a diphtheroidal arrangement are observed in gram stains. Key biochemical reactions include positive catalase, nitrate reduction, esculin hydrolysis, glucose fermentation, and pyrazinamidase.

The most frequent cause of bacterial meningitis in adults and in children is:

Streptococcus pneumoniae is the most common cause of meningitis in adults and in children. Neisseria meningitidis causes meningitis in adults and in children, but not as frequently as S. pneumoniae. Haemophilus influenzae and E. coli usually cause meningitis in infants (1 month to 23 months of age).

Observe the Optochin "P" disc reaction Illustrated in the upper left photograph on the surface of blood agar. Heavy growth of tiny, alpha hemolytic colonies are observed growing on the agar surface that extend to the outer margins of the paper disc. The Gram stain presented in the lower photomicrograph reveals small Gram positive cocci lying singly, in small clusters, and more typically in long chains. This isolate has been recovered from blood cultures in cases of post-valvular endocarditis. Select the presumptive identification of this isolate. A. Streptococcus pneumoniae B. Streptococcus agalactiae C. Streptococcus viridans D. Streptococcus anginosus

Streptococcus viridans. Characteristic are the small, flat, alpha hemolytic colonies observed on blood agar. The long chains of small Gram positive cocci are characteristic. The resistance to optochin with extension of colonies to the borders of the "P" disk and a negative bile esculin reaction are additional features in making a definitive identification. Positive blood cultures with viridians streptococci are seen in patients with subacute bacterial endocarditis, particularly those with pre-existent native-valve disease.

Beta-lactam antibiotics interfere with cell wall synthesis by all of the following, EXCEPT: A. Binding with a transpeptidase. B. Preventing the final stage of peptidoglycan synthesis. C. Interfering with PBPs. D. Targeting the 30S ribosomal subunit.

Targeting the 30S ribosomal subunit. Transpeptidase enzymes catalyze the final stage of peptidoglycan synthesis during cell wall formation. Beta-lactam antibiotics bind with these enzymes, interfering with their function. The transpeptidase enzymes are also referred to as PBP's, or penicillin-binding proteins. Aminoglycosides and tetracyclines interfere with the 30S ribosomal subunit (protein synthesis inhibitors).

Bacteremia

Term used to describe the presence of bacteria in the bloodstream; however, the host immune system will remove the bacteria from the bloodstream without further host issues.

Thayer Martin and LIM Broth

Thayer Martin is used for the recovery of Neisseria gonorrhoeae and Neisseria meningitidis and LIM broth (Todd-Hewitt Broth) is used for the recovery of Streptococcus agalactiae.

Sepsis

term used to describe the presence of actively dividing bacteria in the bloodstream along with SIRS (Systemic inflammatory response syndrome).

keys to the laboratory identification of S. aureus

the growth of large, buttery, golden-yellow colonies on blood agar, the observation of regular, spherical Gram positive cocci on Gram stain, and either tube and/or slide coagulase tests being positive.