An emergency department physician ordered a culture and sensitivity test on a catheterized urine specimen obtained from a 24-year-old female patient. A colony count was done and gave the following results after 24 hours: This isolate is: A. Staphylococcus saprophyticus B. Micrococcus luteus C. Staphylococcus aureus D. Streptococcus pyogenes

An outbreak of Staphylococcus aureus in the nursery department prompted the Infection Control Committee to proceed with an environmental screening procedure. The best screening media to use for this purpose would be: A. CNA agar B. THIO broth C. Mannitol salt agar D. PEA aga

A listless 12-month-old boy with a fever of 103°F was taken to the emergency department. He had been diagnosed with an ear infection 3 days earlier. A spinal tap was performed, but only one tube of CSF was obtained from the lumbar puncture. The single tube of CSF should be submitted first to which department? A. Chemistry B. Microbiology C. Hematology D. Cytology/Histology

A 65-year-old female outpatient was requested by her physician to submit a 24-hour urine specimen for protein and creatinine tests. He also requested testing for mycobacteria in the urine. Should the microbiology laboratory accept this 24-hour specimen for culture? A. Yes, if the specimen is kept on ice B. Yes, if the specimen is for aerobic culture only C. No, the specimen must be kept at room temperature D. No, the specimen is unsuitable for the recovery of mycobacteria

A lymph node biopsy obtained from a 30-year-old male patient was submitted to the microbiology laboratory for a culture and AFB smear for mycobacteria. The specimen was fixed in formalin. This specimen should be: A. Accepted for AFB smear and cultured B. Rejected C. Held at room temperature for 24 hours and then cultured D. Cultured for anaerobes only

A 49-year-old man who traveled to Mexico City returned with a bad case of dysentery. His symptoms were fever; abdominal cramping; and bloody, mucoidal, frequent stools. In addition to this, many WBCs were seen on the Gram stain smear. Stool culture gave the following results: What is the most likely organism? A. Salmonella spp. B. Proteus mirabilis C. Escherichia coli D. Enteroinvasive E. coli (EIEC)

An 80-year-old male patient was admitted to the hospital with a fever of 102°F. A sputum culture revealed many gram-negative rods on MacConkey agar and blood agar. The patient was diagnosed with pneumonia. The following biochemical results were obtained from the culture: What is the most likely identification? IMVIC +-++ A. Klebsiella oxytoca B. Proteus mirabilis C. Escherichia coli D. Klebsiella pneumoniae

An isolate of Staphylococcus aureus was cultured from an ulcer obtained from the leg of a diabetic 79- year-old female patient. The organism showed resistance to methicillin. Additionally, this isolate should be tested for resistance or susceptibility to: A. Erythromycin B. Gentamicin C. Vancomycin D. Kanamycin

An immunocompromised 58-year-old female chemotherapy patient received 2 units of packed RBCs. The patient died 3 days later, and the report from the autopsy revealed that her death was due to septic shock. The blood bags were cultured, and the following results were noted:

A pediatric patient with severe bloody diarrhea who had been camping with his parents was admitted to the hospital with complications of hemolytic uremic syndrome (HUS). Several stool specimens were cultured with the following results noted: What is the most likely identification? A. Yersinia spp. B. E. coli O157:H7 C. Salmonella spp. D. Shigella spp.

A 14-year-old emergency department patient had been to the doctor’s office 2 days previously with abdominal pain, diarrhea, and a low-grade fever. He was diagnosed with pseudoappendicular syndrome. Cultures from the stool containing blood and WBCs showed the following results: What is the most likely identification? A. Yersinia enterocolitica B. Salmonella spp. C. Shigella spp. D. Escherichia coli

A sputum culture from a 13-year-old cystic fibrosis patient grew a predominance of short, gram-negative rods that tested oxidase negative. On MacConkey, chocolate, and blood agar plates, the organism appeared to have a lavender-green pigment. Further testing showed: What is the most likely identification? A. Stenotrophomonas maltophilia B. Acinetobacter baumannii C. Pseudomonas aeruginosa D. Burkholderia (P.) cepacian

A patient with a human bite wound on the right forearm arrived at the clinic for treatment. The wound was inflicted 36 hours earlier, and a culture was taken by the physician on duty. After 48 hours, the culture results were: What is the most likely identification of this facultative anaerobe? A. Pseudomonas aeruginosa B. Acinetobacter baumannii C. Kingella kingae D. Eikenella corroden

A dog bite wound to the thumb of a 20-year-old male patient became infected. The culture grew a gram-negative, slender rod, which was a facultative anaerobe. The following results were noted: “Gliding” on the agar was noted. What is the most likely identification? A. Pseudomonas aeruginosa B. Capnocytophaga canimorsus C. Acinetobacter baumannii D. Proteus mirabilis

A patient exhibits fever, chills, abdominal cramps, diarrhea, vomiting, and bloody stools 10 to 12 hours after eating. Which organisms will most likely grow from this patient’s stool culture? A. Salmonella or Yersinia spp. B. E. coli O157:H7 or Shigella spp. C. Staphylococcus aureus or Clostridium perfringens D. Salmonella or Staphylococcus spp

When testing for coagulase properties, staphylococci isolates from a 67-year-old male diabetic patient showed a positive tube test (free coagulase). The organism should be identified as: A. Staphylococcus aureus B. Staphylococcus haemolyticus C. Staphylococcus saprophyticus D. Micrococcus luteus

An isolate recovered from a vaginal culture obtained from a 25-year-old female patient who is 8 months pregnant is shown to be a gram-positive cocci, catalase negative, and β-hemolytic on blood agar. Which tests are needed for further identification? A. Optochin, bile solubility, PYR B. Bacitracin, CAMP, PYR C. Methicillin, PYR, trehalose D. Coagulase, glucose, PYR

Which organism is the most often recovered gram-positive cocci (catalase negative) from a series of blood cultures obtained from individuals with endocarditis? A. Streptococcus agalactiae B. Clostridium perfringens C. Enterococcus faecalis D. Pediococcus spp.

A presumptive diagnosis of gonorrhea can be made from an exudate from a 20-year-old emergency department patient if which of the following criteria are present? A. Smear of urethral exudate (male only) shows typical gram-negative, intracellular diplococci; growth of oxidase-positive, gram-negative diplococci on selective agar (modified Thayer–Martin) B. Smear from vaginal area shows gram-negative diplococci; growth of typical colonies on blood agar C. Smear from rectum shows typical gram-negative diplococci; no growth on chocolate agar D. Growth of gram-negative cocci on MacConkey agar and blood agar

“Clue cells” are seen on a smear of vaginal discharge obtained from an 18-year-old female emergency department patient. This finding, along with a fishy odor (amine) after the addition of 10% KOH, suggests bacterial vaginosis caused by which organism? A. Staphylococcus epidermidis B. Streptococcus agalactiae C. Gardnerella vaginalis D. E. coli

A 1-month-old infant underwent a spinal tap to rule out bacterial meningitis. The CSF was cloudy, and the smear showed many pus cells and short gram-positive rods. After 18 hours, many colonies appeared on blood agar that resembled Streptococcus spp. or L. monocytogenes. Which of the following preliminary tests should be performed on the colonies to best differentiate L. monocytogenes from Streptococcus agalactiae spp.? A. Hanging-drop motility (25°C) and catalase B. PYR and bacitracin C. Oxidase and glucose D. Coagulase and catalase

Acid-fast positive bacilli were recovered from the sputum of a 79-year-old man who had been treated for pneumonia. Which of the following test reactions after 3 weeks of incubation on Löwenstein–Jensen agar are consistent with Mycobacterium tuberculosis? A. Niacin (+), Nitrate reduction (+), Photochromogenic (-) B. Niacin (-), Optochin (+), Catalase (+) C. PYR (+), Urease (+), Bacitracin (+) D. Ampicillin (R), Penicillin (R)

Which biochemical tests should be performed in order to identify colorless colonies growing on MacConkey agar (swarming colonies on blood agar) from a catheterized urine specimen? A. Indole, phenylalanine deaminase, and urease B. Glucose, oxidase, and lactose utilization C. Phenylalanine deaminase and bile solubility D. H2S and catalase

A gram-negative nonfermenter was isolated from a culture taken from a burn patient. Which of the following is the best choice of tests to differentiate Pseudomonas aeruginosa from Acinetobacter spp.? A. Growth on MacConkey agar, catalase, growth at 37°C B. Oxidase, motility, growth at 42°C C. Growth on blood agar, oxidase, growth at 35°C D. String test and coagulase test

A Haemophilus spp., recovered from a throat culture obtained from a 59-year-old male patient undergoing chemotherapy, required hemin (X factor) and NAD (V factor) for growth. This species also hemolyzed horse erythrocytes on blood agar. What is the most likely species? A. H. ducreyi B. H. parahaemolyticus C. H. haemolyticus D. H. aegyptius

Large gram-positive bacilli (boxcar shaped) were recovered from a blood culture taken from a 70-yearold female diabetic patient. The following results were recorded: What is the most likely identification? A. Clostridium perfringens B. Fusobacterium spp. C. Bacteroides spp. D. Clostridium sporogenes

Anaerobic gram-negative rods were recovered from the blood of a patient after gallbladder surgery. The bacteria grew well on agar containing 20% bile, but were resistant to kanamycin and vancomycin. What is the most likely identification? A. Clostridium perfringens B. Bacteroides fragilis group C. Prevotella spp. D. Porphyromonas spp.

In Breakpoint Antimicrobial Drug Testing, interpretation of susceptible (S), intermediate (I), and resistant (R) refers to testing antibiotics by using: A. The amount needed to cause bacteriostasis B. Only the specific concentrations necessary to report S, I, or R C. An MIC of 64 μg/mL D. A dilution of drug that is one tube less than the toxic level

. A CSF sample obtained from a 2-week-old infant with suspected bacterial meningitis grew gramnegative rods on blood and chocolate agars. The following results were noted: What is the correct identification? A. Pseudomonas aeruginosa B. Chryseobacterium meningosepticum C. Acinetobacter baumannii D. E. coli

During the summer break, several middle-aged elementary school teachers from the same school district attended a 3-day seminar in Chicago. Upon returning home, three female teachers from the group were hospitalized with pneumonia, flulike symptoms, and a nonproductive cough. Routine testing of sputum samples revealed normal flora. Further testing using buffered CYE agar with L-cysteine and α-ketoglutarate in 5% CO2 produced growth of opaque colonies that stained faintly, showing thin gram-negative rods. What is the most likely identification? A. Legionella pneumophila B. Haemophilus influenzae C. Eikenella corrodens D. Streptococcus pneumoniae

A vancomycin-resistant gram-positive coccobacillus resembling the Streptococcus viridans group was isolated from the blood of a 42-year-old female patient undergoing a bone marrow transplant. The PYR and leucine aminopeptidase (LAP) tests were negative. The following results were noted: What is the correct identification? A. Leuconostoc spp. B. Enterococcus spp. C. Staphylococcus spp. D. Micrococcus spp.

A catalase-negative, gram-positive coccus resembling staphylococci (clusters on the Gramstained smear) was recovered from three different blood cultures obtained from a 60-year-old patient diagnosed with endocarditis. The following test results were noted: What is the correct identification? A. Leuconostoc spp. B. Gemella spp. C. Enterococcus spp. D. Micrococcus spp.

An immunocompromised patient with prior antibiotic treatment grew aerobic gram-positive cocci from several clinical specimens that were cultured. The organism was vancomycin resistant and catalase negative. Additional testing proved negative for enterococci. What other groups of organisms might be responsible? A. Leuconostoc spp. and Pediococcus spp. B. Streptococcus pyogenes and Streptococcus agalactiae C. Micrococcus spp. and Gemella spp. D. Clostridium spp. and Streptococcus bovis

A catalase-positive, gram-positive coccus (clusters on Gram stain smear) grew pale yellow, creamy colonies on 5% sheep blood agar. The specimen was recovered from pustules on the face of a 5-year-old girl with impetigo. The following test reactions indicate which organism? A. Micrococcus spp. B. Streptococcus spp. C. Enterococcus spp. D. Staphylococcus spp.

A wound (skin lesion) specimen obtained from a newborn grew predominantly β-hemolytic colonies of gram-positive cocci on 5% sheep blood agar. The newborn infant was covered with small skin eruptions that gave the appearance of a “scalding of the skin.” The gram-positive cocci proved to be catalase positive. Which tests should follow for the appropriate identification? A. Optochin, bile solubility, PYR B. Coagulase, glucose fermentation, DNase C. Bacitracin, PYR, 6.5% salt broth D. CAMP, bile-esculin, 6.5% salt broth

A 20-year-old female patient entered the emergency clinic complaining of abdominal pain, fever, and a burning sensation during urination. An above-normal WBC count along with pus cells and bacteria in the urine specimen prompted the emergency physician to order a urine culture. The colony count reported for this patient revealed >100,000 col/mL of a nonhemolytic, catalasenegative, gram-positive organism on 5% sheep blood agar. The following test results indicate which organism? A. Enterococcus faecalis B. Streptococcus pyogenes C. Streptococcus agalactiae D. Streptococcus bovis

A sputum specimen from an 89-year-old male patient with suspected bacterial pneumonia grew a predominance of gram-positive cocci displaying alpha-hemolysis on 5% sheep blood agar. The colonies appeared donut shaped and mucoid and tested negative for catalase. The most appropriate tests for a final identification are: A. Coagulase, glucose fermentation, lysostaphin B. Penicillin, bacitracin, CAMP C. Optochin, bile solubility, PYR D. Bile esculin, hippurate hydrolysis

A tissue biopsy specimen of the stomach was obtained from a 38-year-old male patient diagnosed with gastric ulcers. The specimen was transported immediately and processed for culture and histology. At 5 days, the culture produced colonies of gramnegative (curved) bacilli on chocolate and Brucella agar with 5% sheep blood. The cultures were held at 35°C–37°C in a microaerophilic atmosphere. The colonies tested positive for urease. The most likely identification is: A. E. coli B. Helicobacter pylori C. Enterococcus faecalis D. Streptococcus bovis

A catalase-positive, gram-positive short rod was recovered from the blood of a prenatal patient. The organism appeared on 5% sheep blood as white colonies surrounded by a small zone of beta hemolysis. The following tests were performed, indicating the patient was infected with which organism? A. Listeria monocytogenes B. Streptococcus agalactiae C. Streptococcus pyogenes D. Lactobacillus spp.

An emergency department physician suspected Corynebacterium diphtheriae when examining the sore throat of an exchange student from South America. What is the appropriate media for the culture of the nasopharyngeal swab obtained from the patient? A. Chocolate agar B. Thayer–Martin agar C. Tinsdale medium D. MacConkey agar

A 25-year-old pregnant patient complained of vaginal irritation. Cultures taken for STDs proved negative. A Gram-stained vaginal smear revealed many epithelial cells with gram-variable short rods (coccobacilli) covering the margins. What is the most likely cause of the vaginosis? A. Group B streptococci spp. B. Gardnerella vaginalis C. Staphylococcus aureus D. Staphylococcus saprophyticus

A 50-year-old male transplant patient was experiencing neurological difficulties after a pulmonary infection. A spinal tap revealed a cloudy CSF with a Gram-stained smear revealing grampositive long-beaded bacilli. An acid-fast smear showed filamentous partially acid-fast bacilli. What is the most likely identification of the organism? A. Nocardia asteroides B. Mycobacterium avium C. Mycobacterium bovis D. Legionella spp

. A 22-year-old pregnant woman (third trimester) entered the emergency department complaining of diarrhea, fever, and other flulike symptoms. Blood cultures were ordered along with a urine culture. After 24 hours, the urine culture was negative, but the blood cultures revealed a gram-positive short rod that grew aerobically on blood agar. The colonies were small and smooth, resembling a Streptococcus spp. with a small narrow zone of β-hemolysis. The following test results indicate which organism? A. Listeria monocytogenes B. Streptococcus pneumoniae C. Streptococcus agalactiae D. Corynebacterium spp.

Anaerobic gram-positive, spore-forming bacilli were recovered from the feces of a chemotherapy patient with severe diarrhea. The patient had undergone antibiotic therapy 1 week prior. The fecal culture produced growth only on the CCFA plate. No aerobic growth of normal flora was seen after 48 hours. The following results were noted: What is the correct identification? A. Clostridium perfringens B. Clostridium tetani C. Clostridium sordellii D. Clostridium difficile

Anaerobic gram-positive diphtheroids (nonspore formers) were cultured from two separate blood culture bottles (at 5 days) obtained from a 25-year-old patient admitted to the hospital with dehydration, diarrhea, and other flulike symptoms. Four other blood culture bottles did not grow any organisms at 7 days and were discarded. The following results were obtained from the recovered anaerobe: What is the correct identification? A. Eubacterium lentum B. Propionibacterium acnes C. Actinomyces spp. D. Peptostreptococcus spp.

Anaerobic gram-positive bacilli with subterminal spores were recovered from several blood cultures obtained from a patient diagnosed with a malignancy of the colon. The following results were recorded: What is the correct identification? A. Clostridium septicum B. Clostridium perfringens C. Clostridium sordellii D. Propionibacterium acnes

Anaerobic gram-negative bacilli were recovered from fluid obtained from drainage of a postsurgical abdominal wound. The following test results were recorded: What is the correct identification? A. Prevotella spp. B. Bacteroides fragilis group C. Porphyromonas spp. D. Clostridium spp.

Anaerobic, nonpigmented, gram-negative rods were recovered from an anaerobic blood agar plate after 48 hours of incubation. The Gram-stained smear showed thin bacilli with pointed ends. The colonies on blood agar had the appearance of dry, irregular, white breadcrumb-like morphology with greening of the agar. The following reactions were noted: What is the correct identification? A. Fusobacterium nucleatum B. Bacteroides fragilis C. Clostridium perfringens D. Peptostreptococcus spp.

A 2-month-old infant in good health was scheduled for a checkup at the pediatrician’s office. After arriving for the appointment, the mother noted white patches on the baby’s tongue and in his mouth. The baby constantly used a pacifier. What is the most likely organism causing the white patches? A. Cryptococcus neoformans B. Candida albicans C. Aspergillus fumigatus d. None of these

A 69-year-old male patient who was a cigarette smoker visited the doctor’s office complaining of a cough and congestion of the lungs. Routine cultures of early morning sputum (×3) for bacteria as well as for AFB revealed no pathogens. A fungal culture was also ordered that grew the following on Sabouraud dextrose agar after 3 days: Hyphae = Septate with dichotomous branching Spores = Produced by conidial heads with numerous conidia Colonies = Velvety or powdery, white at first, then turning dark greenish to gray (reverse = white to tan) Vesicle = Holding phialides usually on upper two thirds only What is the most likely identification? A. Aspergillus niger B. Absidia spp. C. Mucor spp. D. Aspergillus fumigatus

A young male patient with a fungus of the feet visited the podiatrist for relief from the itching. A culture was sent to the microbiology laboratory that grew after 8 days on Sabouraud dextrose agar. Colonies were powdery pink with concentric and radial folds, with the reverse side showing brownishtan to red in color. Other observations were: The most likely identification is: A. Trichophyton mentagrophytes B. Trichophyton rubrum C. Candida albicans D. Aspergillus niger

A 79-year-old female nursing home patient was admitted to the hospital with a fever and central nervous system dysfunction. Routine blood work and blood cultures were ordered. After 48 hours, the blood cultures revealed a budding yeast. The following tests performed from Sabouraud dextrose agar (after 3 days of growth) showed: What is the most likely identification? A. Candida albicans B. Cryptococcus laurentii C. Cryptococcus neoformans D. Candida tropicalis

A dehydrated 25-year-old male patient was admitted to the hospital with symptoms similar to those of chronic fatigue syndrome. Serological testing proved negative for recent streptococcal infection, Epstein–Barr virus, and hepatitis. Which of the following viral serological tests should help with a possible diagnosis? A. CMV B. Echovirus C. Respiratory syncytial virus D. Measles virus

A nursing student working in the emergency department accidentally stuck herself with a needle after removing it from an intravenous set taken from a suspected drug user. The best course of action, after reporting the incident to her supervisor, is to: A. Test the student for HIV virus if flulike symptoms develop in 2–4 weeks B. Immediately test the patient and the student for HIV using an EIA or ELISA test C. Perform a Western blot assay on the student’s serum D. Draw blood from the student only and freeze it for further testing

A 30-year-old female patient complained of vaginal irritation and symptoms (fever, dysuria, and inguinal lymphadenopathy) associated with sexually transmitted disease (STD). Examination showed extensive lesions in the genital area. Chlamydia spp. testing, Neisseria gonorrhoeae, and Gardnerella vaginalis cultures were negative. Rapid plasma reagin (RPR) testing was also negative. What is the next line of testing? A. Darkfield examination B. Herpes simplex testing C. Trichomonas spp. testing D. Group B streptococcal testing

A patient is being seen in the emergency department for a low-grade fever, headache, and general malaise after returning from Africa on a photographic safari. The physician has requested blood for malaria; the laboratory would like to have patient information regarding: A. Specific travel history and body temperature every 4 hours B. Liver function tests and prophylactic medication history C. Transfusion history and body temperature every 4 hours D. Prophylactic medication history and specific travel history

Examination of a modified acid-fast stained fecal smear reveals round structures measuring approximately 8–10 μm, some of which are stained and some of which are not. They do not appear to show any internal morphology. The patient is symptomatic with diarrhea, and the cause may be: A. Blastocystis hominis B. Polymorphonuclear leukocytes C. Cyclospora cayetanensis D. Large yeast cells

A patient has been diagnosed as having amebiasis but continues to be asymptomatic. The physician has asked for an explanation and recommendations regarding follow-up. Suggestions should include: A. Consideration of Entamoeba histolytica versus Entamoeba dispar B. A request for an additional three stools for culture C. Initiating therapy, regardless of the patient’s asymptomatic status D. Performance of barium x-ray studies

Although a patient is strongly suspected of having giardiasis and is still symptomatic, three routine stool examinations (O&P exam) have been performed correctly and reported as negative. Biopsy confirmed the patient had giardiasis. Reasons for these findings may include: A. The patient was coinfected with several bacterial species B. Giardia lamblia tends to adhere to the mucosal surface and more than three stool examinations may be required to confirm a suspected infection C. The organisms present did not stain with trichrome stain and therefore the morphology is very atypical D. Special diagnostic procedures such as the Knott concentration and nutrient-free agar cultures should have been used

A transplant patient is currently receiving steroids. The patient is now complaining of abdominal pain and has symptoms of pneumonia and positive blood cultures with gram-negative rods. The individual has been living in the United States for 20 years but grew up in Central America. The most likely parasite causing these symptoms is: A. Trypanosoma brucei rhodesiense B. Giardia lamblia C. Strongyloides stercoralis D. Schistosoma japonicum

SITUATION: A group of elementary students became ill after eating undercooked ground beef prepared in the school cafeteria. The suspected pathogen, E. coli serotype 0157:H7, is usually recovered using which of the following media? A. XLD agar B. MacConkey agar C. MacConkey agar with sorbitol D. Hektoen agar

SITUATION: Several attendees of a medical conference in the Gulf coast area became ill after frequenting a seafood restaurant. A presumptive identification of Vibrio cholera was made after stool specimens from several subjects grew clear colonies on MacConkey agar and yellow colonies on TCBS agar. Which key tests would help eliminate Aeromonas and Plesiomonas spp.? A. Mannitol fermentation, Na+ requirement B. Oxidase, motility C. Oxidase, nitrate D. Hemolysis on blood agar, catalase

A leg culture from a nursing home patient grew gram-negative rods on MacConkey agar as pink to dark pink oxidase-negative colonies. Given the following results, which is the most likely organism? Antibiotic susceptibility: resistant to carbenicillin and ampicillin A. Serratia marcescens B. Proteus vulgaris C. Enterobacter cloacae D. Klebsiella pneumoniae

A gram-negative rod is recovered from a catheterized urine sample from a nursing home patient. The lactose-negative isolate tested positive for indole, urease, ornithine decarboxylase, and phenylalanine deaminase and negative for H2S. The most probable identification is: A. Edwardsiella spp. B. Morganella spp. C. Ewingella spp. D. Shigella spp

Four blood cultures were taken over a 24-hour period from a 20-year-old woman with severe diarrhea. The cultures grew motile (room temperature), gram-negative rods. A urine specimen obtained by catheterization also showed gramnegative rods, 100,000 col/mL. Given the following results, which is the most likely organism? A. Proteus vulgaris B. Salmonella typhi C. Yersinia enterocolitica D. E. coli

A leg-wound culture from a hospitalized 70-yearold diabetic man grew motile, lactose-negative colonies on MacConkey agar. Given the following biochemical reactions at 24 hours, what is the most probable organism? A. Proteus vulgaris B. Serratia marcescens C. Proteus mirabilis D. Enterobacter cloacae

Three blood cultures taken from a 30-year-old cancer patient receiving chemotherapy and admitted with a urinary tract infection grew lactose-negative, motile, gram-negative rods prior to antibiotic therapy. Given the following biochemical reactions, which is the most likely organism? A. Proteus vulgaris B. Proteus mirabilis C. Serratia marcescens D. Klebsiella pneumoniae

Three consecutive stool cultures from a 25-yearold male patient produced scant normal fecal flora on MacConkey and Hektoen agars. However, colonies on CIN agar (Cefsulodin–irgasan–novobiocin) displayed “bulls-eye” colonies after 48 hours incubation. The patient had been suffering from enterocolitis with fever, diarrhea, and abdominal pain for 2 days. What is the most likely identification of this gram-negative rod? A. E. coli B. Proteus mirabilis C. Yersinia enterocolitica D. Klebsiella pneumoniae

Following a 2-week camping trip to the Southwest (US), a 65-year-old male patient was hospitalized with a high fever and an inflammatory swelling of the axilla and groin lymph nodes. Several blood cultures were obtained, resulting in growth of gram-negative rods resembling “closed safety pins.” The organism grew on MacConkey’s agar showing non–lactosefermenting colonies. Testing demonstrated a nonmotile rod that was biochemically inert. What is the most likely identification? A. Yersinia pestis B. Klebsiella pneumoniae C. Proteus vulgaris D. Morganella morganii

The following results were obtained from a pure culture of gram-negative rods recovered from the pulmonary secretions of a 10-year-old cystic fibrosis patient with pneumonia: Which is the most likely organism? A. Burkholderia pseudomallei B. Pseudomonas stutzeri C. Burkholderia cepacia D. Pseudomonas aeruginosa

A culture from an intra-abdominal abscess produced orange-tan colonies on blood agar that gave the following results: The most likely identification is: A. Shewanella putrefaciens B. Acinetobacter spp. C. Pseudomonas aeruginosa D. Chryseobacterium spp.

A visitor to South America who returned with diarrhea is suspected of being infected with V. cholerae. Select the best medium for recovery and identification of this organism. A. MacConkey agar B. Blood agar C. TCBS agar D. XLD agar

A curved gram-negative rod producing oxidasepositive colonies on blood agar was recovered from a stool culture. Given the following results, what is the most likely identification? A. Vibrio cholerae B. Vibrio parahaemolyticus C. Shigella spp. D. Salmonella spp.

A gram-negative S-shaped rod recovered from selective media for Campylobacter species gave the following results: The most likely identification is: A. Pseudomonas aeruginosa B. Campylobacter jejuni C. Campylobacter fetus D. Pseudomonas putida

A mixture of slender gram-negative rods and coccobacilli with rounded ends was recovered from blood cultures following a patient’s root canal surgery. Given the following results after 48 hours, what is the most likely organism? A. Eikenella corrodens B. Actinobacillus spp. C. Cardiobacterium hominis D. Proteus spp.

A 29-year-old male who often hunted rabbits and spent a lot of time in the woods was admitted to the hospital with skin ulcers on his upper extremities. At 48 hours, a small coccobacillus was recovered from the aerobic blood culture bottle only. The organism stained poorly with Gram stain, but did stain with acridine orange. Cultures taken from the ulcers did not grow on primary media. What is the most likely identification? A. Pseudomonas aeruginosa B. Pseudomonas fluorescens C. Chryseobacterium spp. D. Francisella tularensis

A small, gram-negative coccobacillus recovered from the CSF of a 2-year-old child gave the following results: Which is the most likely identification? A. Haemophilus parainfluenzae B. Haemophilus influenzae C. Haemophilus ducreyi D. Haemophilus aphrophilus

Cultures obtained from a dog bite wound produced yellow, tan, and slightly pink colonies on blood and chocolate agar with a margin of fingerlike projections appearing as a film around the colonies. Given the following results at 24 hours, which is the most likely organism? A. Actinobacillus spp. B. Eikenella spp. C. Capnocytophaga spp. D. Pseudomonas spp.

Two blood cultures on a newborn grew βhemolytic streptococci with the following reactions: Which is the most likely identification? A. Group A streptococci B. Group B streptococci C. Group D streptococci D. Nongroup A, nongroup B, nongroup D streptococci

80. Sputum from a patient with pneumonia produced many colonies of gram-negative diplococci on a chocolate plate that were also present in fewer numbers on MTM after 48 hours. Given the following results, what is the most likely identification? A. Moraxella catarrhalis B. Neisseria flavescens C. Neisseria sicca D. Neisseria elongat