Micro 8.12 Microbiology and Parasitology Problem-Solving Flashcards
- 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 the following results were obtained after 24 hours:
Blood agar plate = >100,000 col/mL of gram-positive cocci resembling staphylococci
MacConkey agar = No growth
CNA plate = Inhibited growth
Hemolysis = Neg
Novobiocin = Resistant
Catalase = +
This isolate is:
A. Staphylococcus saprophyticus
B. Micrococcus luteus
C. Staphylococcus aureus
D. Streptococcus pyogenes
A. Staphylococcus saprophyticus
- An outbreak of S. aureus in the hospital nursery 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 agar
C. Mannitol salt agar
- A 12-month-old boy who had a fever of 103°F and was listless 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
B. Microbiology
- 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
D. No, the specimen is unsuitable for the recovery of mycobacteria
- A lymph node biopsy specimen obtained from a 30-year-old male patient was submitted to the microbiology laboratory for culture and AFB smear for mycobacteria. The specimen was fixed in formalin. This specimen should be:
A. Accepted for AFB smear preparation and cultured
B. Rejected
C. Held at room temperature for 24 hours and then cultured
D. Cultured for anaerobes only
B. Rejected
- A 49-year-old man who traveled to Mexico City returned with severe dysentery. His symptoms were fever; abdominal cramping; and bloody, mucoidal, frequent stools. In addition to this, many WBCs were seen in the Gram-stained smear. Stool culture gave
the following results:
Gram staining = gram-negative rods
Lactose = +
Indole = +
Urease = Neg
Lysine decarboxylase = Neg
Motility = Neg
What is the most likely organism?
A. Salmonella spp.
B. Proteus mirabilis
C. Escherichia coli
D. Enteroinvasive E. coli (EIEC)
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:
H2S = Neg
Citrate = +
Motility = Neg
Lactose = +
Indole = +
Urease = +
VP = +
Resistance to ampicillin and carbenicillin
What is the most likely identification?
A. Klebsiella oxytoca
B. Proteus mirabilis
C. Escherichia coli
D. Klebsiella pneumoniae
A. Klebsiella oxytoca
- An immunocompromised 58-year-old female patient on chemotherapy received 2 units of packed RBCs. The patient died 3 days later, and the report from the autopsy revealed that her death resulted from septic shock. The blood bags were submitted for culture, and the following results were noted:
GROWTH OF AEROBIC GRAM-NEGATIVE RODS ON BOTH MACCONKEY AND BLOOD AGARS
Lactose = Neg
Indole = Neg
Urease = +
Sucrose = +
VP = Neg
Motility 22°C = +
Citrate = Neg
H2S = Neg
Motility 37°C = Neg
What is the most likely identification?
A. Escherichia coli
B. Yersinia enterocolitica
C. Enterobacter cloacae
D. Citrobacter freundii
B. Yersinia enterocolitica
- A pediatric patient who had had been camping with his parents was admitted to the hospital with severe bloody diarrhea and complications of hemolytic uremic syndrome (HUS). Several stool specimens were submitted for culture and the following results
noted:
Gram staining = Many gram-negative rods, with no WBCs seen
Blood agar = Normal flora
MacConkey agar = Normal flora
MacConkey agar with sorbitol = Many clear colonies (sorbitol negative)
Hektoen agar = Normal flora Campy agar = No growth
What is the most likely identification?
A. Yersinia spp.
B. E. coli O157:H7
C. Salmonella spp.
D. Shigella spp
B. E. coli O157:H7
- A 14-year-old patient presented to the emergency department; he had been to the doctor’s office 2 days ago with abdominal pain, diarrhea, and a low-grade fever. He was diagnosed at the emergency department with pseudoappendicular syndrome. Cultures from the stool containing blood and WBCs showed the following results:
AEROBIC GRAM-NEGATIVE RODS ON MACCONKEY AGAR (CLEAR
COLONIES)
Campy agar = No growth
Lactose = Neg
Sucrose = +
Citrate = Neg
Indole = Neg
VP = Neg
H2S = Neg
Motility 37°C = Neg
Motility 22°C = +
Hektoen agar = NF
What is the most likely identification?
A. Yersinia enterocolitica
B. Salmonella spp.
C. Shigella spp.
D. Escherichia coli
A. Yersinia enterocolitica
- Culture of the sputum specimen from a 13-year-old patient with CF grew a predominance of short, gram-negative rods that tested oxidase negative. On MacConkey, chocolate, and blood agar plates, the organism appeared to have lavendergreen pigmentation. Further testing showed the following:
Motility = +
Glucose = + (oxidative)
Lysine decarboxylase = +
DNase = +
Maltose = + (oxidative)
Esculin hydrolysis = +
What is the most likely identification?
A. Stenotrophomonas maltophilia
B. Acinetobacter spp.
C. Pseudomonas aeruginosa
D. Burkholderia (P.) cepacia
A. Stenotrophomonas maltophilia
- 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 as follows:
GRAM-STAINING = GRAM-NEGATIVE STRAIGHT, SLENDER RODS
Chocolate agar plate = “Pitting” of the agar by small, yellow, opaque colonies
Oxidase = +
Motility = Neg
Catalase = Neg
Glucose = +
Growth in increased CO2 = + Growth at 42°C = Neg
What is the most likely identification of this facultative anaerobe?
A. Pseudomonas aeruginosa
B. Acinetobacter spp.
C. Kingella kingae
D. Eikenella corrodens
D. Eikenella corrodens
E. corrodens is part of the normal flora of the human mouth and typically “pits” the agar. This organism is capnophilic (needing increased CO2).
- A dog bite wound to the thumb of a 20-year-old male patient became infected. Culture grew a gram-negative, slender rod, which was a facultative anaerobe. The following results were noted:
Oxidase = +
Catalase = +
“Gliding” on the agar was noted.
Motility = Neg
Capnophilic = +
What is the most likely identification?
A. Pseudomonas aeruginosa
B. Capnocytophaga canimorsus
C. Acinetobacter spp.
D. Proteus mirabilis
B. Capnocytophaga canimorsus
C. canimorsus is associated with septicemia or meningitis following dog bites. All Capnocytophaga strains are capnophilic, facultative anaerobic, gram-negative, slender or filamentous rods with tapered ends.
- 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. Escherichia coli O157:H7 or Shigella spp.
C. Staphylococcus aureus or Clostridium perfringens
D. Salmonella or Staphylococcus spp.
B. Escherichia coli O157:H7 or Shigella spp.
- When testing for coagulase properties, staphylococci isolates from a 67-year-old male patient with diabetes showed a positive tube test (free coagulase) result. The organism should be identified as:
A. Staphylococcus aureus
B. Staphylococcus haemolyticus
C. Staphylococcus saprophyticus
D. Micrococcus luteus
A. Staphylococcus aureus
- An isolate of S. aureus was cultured from an ulcer obtained from the leg of a 79-year-old female patient with diabetes. The organism showed resistance to methicillin. This isolate should be additionally tested for resistance or susceptibility to:
A. Erythromycin
B. Gentamicin
C. Vancomycin
D. Kanamycin
C. Vancomycin
- An isolate recovered from a vaginal culture obtained from a 25-year-old female patient who is 8 months pregnant is shown to be 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
B. Bacitracin, CAMP, PYR
Group B streptococci (S. agalactiae) are important pathogens and can cause serious neonatal infections. Women who are found to be heavily colonized vaginally with S. agalactiae pose a threat to the newborn, especially within the first few days after delivery. The infection acquired by the infant is associated with pneumonia.
- Which organism is the most often recovered gram-positive coccus (catalase negative), displaying α-, β-, or γ-hemolysis on blood agar from a series of blood culture specimens obtained from patients with endocarditis?
A. Streptococcus agalactiae
B. Clostridium perfringens
C. Enterococcus faecalis
D. Pediococcus spp.
C. Enterococcus faecalis
- 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 (MTM)
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
A. Smear of urethral exudate (male only) shows typical gram-negative, intracellular diplococci; growth of oxidase-positive, gram-negative diplococci on selective agar (MTM)
- “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. Escherichia coli
C. Gardnerella vaginalis
- 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 spp.?
A. Hanging-drop motility (25°C) and catalase
B. PYR and bacitracin
C. Oxidase and glucose
D. Coagulase and catalase
A. Hanging-drop motility (25°C) 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 M. tuberculosis?
A. Niacin = +
Nitrate reduction = +
Photochromogenic = Neg
B. Niacin= Neg
Optochin = +
Catalase = +
C. PYR = +
Urease = +
Bacitracin = +
D. Ampicillin = Resistant
Penicillin = Resistant
A. Niacin = +
Nitrate reduction = +
Photochromogenic = Neg
M. tuberculosis is niacin positive and nonphotochromogenic. This organism takes up to 3 weeks to grow on selective agar.
- Which biochemical tests should be performed 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. Indole, phenylalanine deaminase, and urease
- A gram-negative nonfermenter was isolated from a culture taken from a patient who had suffered burns. Which of the following is the best choice of tests to differentiate P. 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
B. Oxidase, motility, growth at 42°C
P. aeruginosa has a distinctive grape odor. The best tests to differentiate it from Acinetobacter spp. are growth at 42°C, oxidase, and motility.