SKIN, SOFT TISSUE, AND BONE
The colonies illustrated on the blood and chocolate agar plates represent a slow-growing bacterial species that is endogenous in the oral cavity and upper respiratory tract. It may be recovered from human bite skin infections incurred during fist fights. Note the pitting of the agar surrounding the colonies growing in the chocolate agar plate. The Alk/Alk non fermentative reaction seen in the Kligler Iron Agar tube to the left in the lower photograph indicates the non-fermentation of glucose, also indicated by the lack of carbohydrate assimilation in the individual carbohydrate reaction tubes to the right of the KIA tube. A reduction of nitrate is seen and decarboxylation of ornithine is also positive. Based on these observations, select from the multiple choices listed the correct identification of this bacterial isolate:
Eikenella corrodens
The organism pictured below was a Gram positive rod isolated from a sore on the hand of a fish market employee. It is shown on triple sugar iron agar. The organism is also catalase negative and non-spore forming. The most likely identification is:
Erysipelothrix rhuziopathiae
The photograph illustrates a classic case of scrofula infection, most commonly caused by Mycobacterium scrofulaceum. The age range when this condition is most likely to appear is:
18 months-7 years
Which bacterial genus contains fastidious, facultative intracellular, gram-negative bacilli that causes a zoonosis called tularemia?
Francisella
A gram-negative rod isolated from a burn patient produced a bluish green pigment and the following test results: Characteristic fruity odorTriple sugar iron (TSI) agar: Alkaline/alkalineMotility: PositiveOxidase: PositiveOxidative/fermentation (OF) glucose: Oxidative utilization only What is the MOST probable genus of this isolate?
Pseudomonas
The well circumscribed cutaneous papule with the distinct outer erythematous border illustrated in the upper photograph developed over a period of 5 days at the site of a tick bite. The lower photograph illustrates colonies growing on a buffered charcoal yeast extract agar plate that had been inoculated with material from the ulcer bed three days before. Tiny, pale-staining Gram negative coccobacilli were seen on Gram stain. The most likely causative agent is:
Francisella tularensis
The growth on a blood agar plate as illustrated in the photograph was prepared from the surface drainage of a subcutaneous abscess of a 50-year-old man following a deep penetrating splinter wound. The colonies on this young culture are small, rough, gray-white, and non-hemolytic. Older larger colonies became sunken centrally having a "molar tooth" appearance. The Gram stain reveals gram-positive branching filaments. Key biochemical reactions include hydrolysis of Esculin, nitrate reduction, and negative catalase. From these observations, select from the multiple choices the identification of this isolate:
Actinomyces israeli
The organism Acinetobacter baumannii is known to have caused which of the following outbreaks?
Afghanistan and Iraq U.S. soldiers outbreak
The bacterial species commonly found in association with deep tissue actinomycosis is:
Aggregatibacter actinomycetemcomitans
The well circumscribed, ulcerating pustule illustrated in the upper photograph evolved over 8 days following direct contact with raw animal hides that had been shipped from Central Asia. The lesion began as a small papule, which progressively enlarged, ultimately ulcerated and became covered centrally with a black eschar. The lower photomicrograph is a gram stain prepared from a colony that grew within 48 hours on blood agar. The most likely agent of this infection is:
Bacillus anthracis ("malignant pustule")
Which of the following is considered a normal skin flora organism?
Bacillus subtilis
All of the following organisms are aerobic organisms, EXCEPT?
Bacteroides fragilis
An abdominal wound culture grows E. coli on the aerobic culture. The anaerobic culture has growth of two, gram- negative rods, one of which is aerobic. The other gram negative rod has 2+ growth on BBE plate and is resistant to kanamycin, colistin, and vancomycin disc. What is this organism's identification?
Bacteroides fragilis group
Aspiration material recovered from a ruptured appendix abscess was inoculated to anaerobic culture media per laboratory protocol. Gray colonies (> 1 mm) grew anaerobically in 24 hours on BBE agar, blackening the media. The photograph illustrates the gram stain features of the organism. The bacterial species most likely associated with the abscess is:
Bacteroides fragilis group
The bacterial species most likely associated with bacillary angiomatosis is:
Bartonella henselae
Each of the following bacterial species are commonly associated with wound infections following a dog bite except?
Bordetella bronchiseptica
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
A fusiform-shaped, Gram negative, oxidase negative bacillus that produces colonies with marginal finger-like projections was recovered from the oral cavity of a patient with periodontal disease. The most likely identification is:
Capnocytophaga ochracea
Human dog bite infections may be caused by each of the following bacterial species except:
Capnocytophaga ochracea
In the image to the right, letter B represents what type of endospore placement?
Central
A sample from a wound infection, suspected case of gas gangrene, was cultured and showed anaerobic colonies that are small, smooth, light gray-yellow and surrounded by a distinctive double zone of beta hemolysis (arrows). Gram stain, as illustrated in the lower photomicrograph, are large, non-spore forming, "box-car" shaped gram positive bacilli. What is this organism that is also related to outbreaks of food-borne diarrhea following ingestion of contaminated meat products?
Clostridium perfringens
Which of the following organisms is most likely to be associated with gas gangrene:
Clostridium perfringens
Which of the following organisms is responsible for myonecrosis with gas gangrene, food poisoning as well as necrotizing enteritis, a life threatening that causes ischemic necrosis of the jejunum?
Clostridium perfringens
Which of the following organisms produces a double zone of hemolysis on blood agar?
Clostridium perfringens
A 25-year-old man was experiencing some difficulty in chewing and swallowing food. He had incurred a deep laceration of the lower leg in a lawn mower incident one week before. The wound was healing but signs of infection persisted. The image shows the Gram stain of a spreading, gray colony isolated from an aspirate of the wound, incubated under anaerobic conditions. Three additional bacterial species were recovered on blood agar incubated aerobically. What is the most likely identification of this anaerobic organism?
Clostridium tetani
All of the following are common causes of infective endocarditis, EXCEPT?
Corynebacterium jeikeium
Illustrated in this photograph are latex agglutination reactions of an unknown beta hemolytic streptococcus recovered from a blood culture. Each reaction is labeled by the group number tested. Of the choices listed, which source is most likely the primary infection for the suspected organism?
Deep wound cellulitis
Clenched-fist cellulitis is commonly found in patients whom have been in a physical altercation. Which organism below is the most likely cause of this condition?
Eikenella corrodens
Illustrated in this photograph are colonies growing on the surface of a chocolate agar plate. The colonies were recovered from a subcutaneous infection of the forearm and had a bleach odor. The most likely identification is:
Eikenella corrodens
Which of the following organisms "pits" the agar, and smells like bleach?
Eikenella corrodens
All of the following descriptions about Pasteurella species are true, EXCEPT
Grows well on MacConkey agar.
A 21-year-old female developed painful swelling of the left knee along with a low grade fever. The knee was painful to palpation, an effusion was evident, and the overlying skin was slightly erythematous. Fluid was aspirated and a gram stain was performed (as seen in the images to the right). Based on the Gram stain morphology, which of the following bacterial species is LEAST likely to serve as the etiologic agent in the case described?
Haemophilus influenzae
The term "HACEK" is often associated with infective endocarditis. All of the following organisms are included in the "HACEK" group, EXCEPT?
Haemophilus influenzae
Corynebacterium jeikeium is often associated with which of the following conditions?
Infected indwelling devices in AIDS patients
An 87-year old patient had a foot wound that grew gram-negative rods on McConkey agar as pink to dark pink oxidase-negative colonies along with the following results: TSI: A/AIndole: neg.MR: neg.VP: pos.Citrate: pos.H2S: neg.Urea: pos.Motility: neg.Ornithine: neg.Antibiotic susceptibility: Carboxicillin and ampicillin resistant, all others sensitive.
Klebsiella pneumonia
What is the probable identity of an organism isolated from a wound culture that demonstrates the following test results? Phenylalanine Deaminase = negative TSI = A/A gas Citrate = positive Lysine = positive SIM = negative/negative/negative Urea = weakly positive
Klebsiella pneumoniae
The anaerobe producing the double zone of hemolysis, seen in this photograph, can be presumptively identified as Clostridium perfringens. The enzyme producing the outer zone of hemolysis is:
Lecithinase
A group of Canadian travelers were visiting the island of Kauai in Hawaii for a summer vacation. They noticed a cave in the middle of the island that contained a 10 ft deep pool of water. Much to their surprise, they were the only individuals enjoying this newly discovered swimming hole. A few days later, all swimmers became ill. Their physician believed they all had Weil disease. Which of the following organisms can cause this disease?
Leptospira interrogans
Erythema migrans, spirochetemia, and chronic arthritis are three stages in the progress of:
Lyme disease
A culture was taken of a conjunctival exudate. The bacterial species, represented by the tiny colonies seen on this chocolate agar plate were recovered after 48 hours incubation at 35°C. The isolate was cytochrome oxidase positive and highly susceptible to penicillin. What is the most likely identification of this organism?
Moraxella lacunata
A 30-year-old woman developed progressive, painful swelling of the right foot after incurring traumatic penetration of the soft tissue by a splinter. The wound initially healed. The upper photograph is a direct Gram stain of purulent material expressed from a sinus tract. The lower photograph illustrates the colony that grew out in 72 hours, which had a "musty" odor. The most likely identification is:
Nocardia brasiliensis
Which of the following organisms is a cause of cutaneous infections?
Nocardia brasiliensis
The following is the BEST test to differentiate between Aeromonas hydrophila and Escherichia coli from a wound culture:
Oxidase production
The organism growing on Blood Agar and MacConkey Agar in the attached photograph was recovered from the burn wound of a patient. The Gram stain is also attached. This organism is a non-fermenter and can grow at increased temperatures (42 °C). Upon additional testing, the organism was positive for pyocyanin production. Which of the following is the most likely presumptive identification of this organism?
Pseudomonas aeruginosa
Edwardsiella tarda is known to be associated with which of the following animals?
Reptiles
Rocky Mountain spotted fever (RMSF) is transmitted by the bite of a tick infected with:
Rickettsia rickettsii
Each of the following statements regarding Rickettsiaceae are correct EXCEPT:
Rocky mountain spotted fever is almost always geographically restricted to the Rocky mountain region
Which of these organisms is associated with the condition known as toxic shock syndrome?
Staphylococcus aureus
A 30-year-old laboratory worker in New York, doing extensive research on laboratory mice, developed sudden onset of fever, chills, headache and muscle aches. He remembered being bitten by one of the mice about a week previously, although the skin wound healed without incidence. A direct gram stain from the laboratory worker is shown and includes the microrganism causing disease.
Streptobacillus moniliformis
A patient presents with cellulitis and culture growth small beta hemoytic colonies on 5% Sheep blood agar. The gram stain of the organism is included. What is the most ikely cause of the infection.
Streptococcus pyogenes
The ability of streptococci to spread within the tissues and cause rapidly advancing cellulitis is due to the production of several virulence factors. Each of the following correctly describes the effects of the specific virulence factor EXCEPT:
Streptolysin S is associated with the rash of scarlet fever and the pathogenesis of streptococcal toxic shock like syndrome.
The colonies growing on Middlebrook agar as shown in the upper left photograph were recovered after 5 days incubation from an aspirate from a superficial skin infection. The gram stain revealed branching bacilli as seen in the lower image. These organisms are acid-fast negative. Illustrated in the upper right photograph are colonies growing on casein medium demonstrating hydrolysis. The MOST likely identification is:
Streptomyces species
Examine this photo of a 5% sheep blood agar plate from a wound culture workup. All of the following direct tests would be helpful in making an immediate presumptive identification of the organism growing on the plate EXCEPT
Thermostable endonuclease
All of the following statements concerning Rickettsia species are true, EXCEPT:
They are cultured in many hospital laboratories.
Infections with Eikenella corrodens is associated with:
Trauma associated with human teeth
The gram negative bacillus illustrated in the lower photomicrograph was recovered from a skin wound incurred while the patient was swimming in sea water around the Western U.S. coast of the Gulf of Mexico. Note that the gray-yellow colonies grow well on blood agar (upper composite image to the left), but the colonies on TCBS agar (Thiosulfate Citrate Bile Sucrose - composite image to the right) are pale green, indicating the lack of sucrose utilization. The short, slightly curved gram negative bacilli seen in a gram stain (lower photomicrograph) are consistent with Vibrio species, but not species specific. Select the presumptive identification of this isolate.
Vibrio vulnificus
Which of the following animals is a a likely source of human tularemia infections?
Wild rabbits
A small gram-negative rod isolated from an eye grows on chocolate agar and it produces satellite growth around staphylococci colonies on sheep blood agar. The organism requires:
X factor and V factor
An 8-year-old boy underwent a laparotomy for clinical signs and symptoms of acute appendicitis. Instead, the appendix did not appear inflamed, but the mesenteric lymph nodes were enlarged and edematous. The photomicrograph is a close-in H & E section of an area within one of the lymph nodes, showing hyperplasia and focal necrotizing inflammation. What bacterial species most likely causing this reaction?
Yersinia enterocolitica
What bacteria is responsible for the bubonic plaque?
Yersinia pestis
Which of the following is the most common etiologic agent identified in prosthetic valve endocarditis?
Staphylococcus epidermidis
A methicillin-resistant Staphylococcus aureus was recovered from a wound infection. Which antibiotic would be used for treatment?
Vancomycin
A 49-year-old farmer developed swelling of the neck beneath the left jaw with enlargement of the left posterior cervical lymph nodes. The photograph to the right is representative of a direct gram stain prepared from purulent material aspirated from one of the enlarged lymph nodes. The organism was not acid fast. What is the MOST likely identification?
Actinomyces israelii
A Gram stain of drainage from an open wound revealed gram-positive bacilli with spores. This description would commonly rule out which one of the following organisms? (Choose the BEST response.)
Clostridium perfringens
The organism that is a strict anaerobe, non-motile, gram-negative bacillus, occurring in abscesses and associated with peritonitis is MOST likely:
Bacteroides spp.
Observed growing on chocolate agar after 4 days of incubation are non-descript tiny, circular, smooth colonies. Growth on sheep blood agar is typically absent or minimal. In the Gram stain, as illustrated in the upper photomicrograph, thin, long fusiform Gram negative bacilli are observed. This organism was isolated from a skin abscess at the site of a dog bite. The Kligler Iron Agar reaction was A/A indicating carbohydrate assimilation, with distinctive positive test reactions for dextrose, sucrose, and maltose. With these observations, select the identification of this isolate.
Capnocytophaga species
Eikenella corrodens is associated with which of the following?
Clenched fist infection
From the choices listed below, which organism is classified as an obligate anaerobe?
Clostridium novyi
An 18-year-old woman woke up in the morning to find that her left knee was hot, swollen, and very painful. She could not walk to work and a friend offered her a ride to the clinic. She had never had a swollen joint before. Physical exam revealed a tender knee joint which yielded purulent synovial fluid on aspiration. Gram negative intracellular diplococci were seen on Gram stain. She also had a cervical discharge that was cultured. The cause of her infection would grow best on:
Modified Thayer Martin (MTM) agar at 35º C with CO2
Tiny translucent gray colonies were recovered on blood agar from a patient with purulent conjunctivitis. Gram negative diplococci were seen on Gram stain. The preparation illustrated in this photomicrograph was obtained from colonies growing at the margin of inhibition of a 10 µg/mL penicillin disk. The most likely identification is:
Moraxella lacunata
The colonies illustrated in the upper photograph, recovered from a cat bite skin lesion of a child, reveal good growth of entire, convex, gray-white, smooth colonies on blood and chocolate agars. The colonies on blood agar are non-hemolytic and growth was not observed on MacConkey agar. Coccoid to rod-shaped Gram-negative bacilli are observed in the Gram stain. Positive tube reactions for indole, Voges Proskauer, ornithine, arginine, and strong production of esculin are observed in the lower photograph. The cytochrome oxidase reaction is also positive. With these observations, select the best choice for the identification of this isolate.
Pasteurella multocida
The upper image of a blood agar plate illustrates the smooth, gray, nonhemolytic colonies that were recovered after 36 hours incubation from a wound of the forearm of a 14-year-old boy following a dog bite. The colony had a musty or mushroom odor and is oxidase positive. It did not grow on MacConkey agar. The lower image illustrates the gram stain prepared from the colony. The most likely identification is:
Pasteurella multocida
The colonies illustrated in the composite blood agar/MacConkey agar to the left were recovered from an inflammatory infection of the oral cavity of a 16-year-old student. The colonies on both agar plates incubated anaerobically are small, entire, and smooth with a light gray-yellow pigmentation. Small gram-negative rods arranged singly and in loose clusters had been observed microscopically in a gram-stained preparation. Spot indole and lipase reactions are positive. Note in the image to the right the alk/alk non-fermentative carbohydrate reaction on Kligler Iron agar, with lack of fermentation of the sugars presented in the tubes to the right (asaccharolytic). Select from the multiple choices the name of this anaerobic, asaccharolytic, gram-negative isolate.
Porphyromonas asaccharolytica
Infections with this organism typically either present as primary septicemia or wound infections. Septicemia likely occurs after the organism is ingested while consuming shellfish. Wound infections are associated with some type of aquatic exposure. What organism does this describe?
Vibrio vulnificus
Illustrated in the photographs are smooth, entire, gray-white colonies growing on blood agar that are faintly beta hemolytic (left). Light pink-red pigmented entire, smooth colonies grew on MacConkey agar (right). These isolates were recovered from a skin infection incurred by a 28 year old man after swimming in a lake. The pink-red pigmentation of colonies on MacConkey agar suggest lactose fermentation. Biochemical reactions included Acid/Acid KIA reactions indicating fermentation of glucose. Oxidase was positive. Other positive reactions include indole, DNAse, and esculin. Additional biochemical tests identified this isolate as Aeromonas species. The pink-red colonies growing on MacConkey may suggest one of the Enterobacteriaceae. Which of the following choices will exclude this possibility?
Positive oxidase reaction
Illustrated in the photograph is the 4 day slow growth of colonies recovered on an anaerobic culture. Note the small size of the colonies growing on anaerobic blood agar, distinctive for brown-black pigmentation surrounded by a wide zone of beta hemolysis. Gram stain revealed small, gram-negative coccobacilli. Most strains are biochemically inactive, although glucose and lactose fermentation are positive (saccharolytic). A common source would be from an infection of the oral cavity or from an infected human bite wound. From these observations, select from the multiple choices the identification of this isolate.
Prevotella melaninogenica
What virulence factor is not inherent to bacterium?
Production of opsonins
A 22-year-old construction worker incurred 3rd degree burns to the chest and arms when a boiler he was installing blew up. On the 5th hospital day the weeping wounds became infected, exuding what was described as green pus. The image illustrates the Gram stain prepared on a direct smear of the exudate. What is the MOST likely bacterial cause of the infection?
Pseudomonas aeruginosa
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). They were 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 reactions for catalase, nitrate reduction, esculin, and pyrazinamidase. Based on these observations, select the presumptive identification of this isolate.
Rothia dentocariosa
An infective agent of skin wound infections and an agent of toxic shock syndrome, the large, entire, golden-yellow, smooth convex colonies on blood agar were recovered from a swab specimen after 48 hours incubation at 37o C. In the image to the right, clusters of gram-positive cocci were observed microscopically in a gram stain prepared from one of the colonies. The coagulase reaction was positive. With these observations, select the name of this isolate from the choices given.
Staphylococcus aureus
An infective agent of skin wound infections and an agent of toxic shock syndrome, the large, entire, golden-yellow, smooth convex colonies on blood agar were recovered from a swab specimen after 48 hours incubation at 37° C. In the photomicrograph, clusters of Gram positive cocci were observed microscopically in a Gram stain prepared from one of the colonies. The coagulase reactions are pictured in the lower images. With these observations, select the name of this isolate.
Staphylococcus aureus
Purulent material is obtained from a carbuncle and submitted for bacterial culture. Many Gram positive cocci and white blood cells were seen on 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
A left arm abscess collected from an 8-year-old male patient grew small white colonies on 5% sheep blood agar after 24 hours incubation at 35°C in 5-10% CO2. The Gram stain of the organism showed small tightly grouped Gram positive cocci. Which of the following organisms is the most likely identification?
Staphylococcus epidermidis
Each of the bacterial species listed below may be associated with culture-negative endocarditis EXCEPT:
Staphylococcus epidermidis
Out of the given choices below, which one of the following bacteria is the MOST frequent cause of prosthetic heart valve infections occurring after heart surgery?
Staphylococcus epidermidis
The diffuse erythroderma and edema of the hand shown in the upper photograph is of a 24 year old female with fever, headache and hypotension. The blood agar plate shown in the lower photograph was inoculated with purulent material aspirated from a vertebral disk abscess. The most likely condition is:
Toxic shock syndrome
A 27-year-old man who had recently worked as a medical laboratory scientist on the Navajo Native American reservation presented to the emergency department with high fever, diarrhea, and prostration. Axillary lymph nodes were hemorrhagic and enlarged. A smear was prepared from a lymph node aspirate and many Gram negative bacilli were noted. The bacilli demonstrated a marked bipolar staining reaction described as a "safety-pin appearance" with Wayson stain. What is the most likely identification of this organism?
Yersinia pestis
Throughout history, plague pandemics have killed millions. Transmission of the human plague may still occur through bites of rodent fleas or contact with infected animals. What is the causative agent of plague?
Yersinia pestis
