MLPAO Microbiology and Parasitology Clinical Applications Flashcards
6 cards from real MLPAO practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 MLPAO Microbiology and Parasitology Clinical Applications flashcards as text
A throat culture grows beta-hemolytic colonies. What additional testing should be performed?
Answer: Bacitracin susceptibility or PYR test to presumptively identify Group A Streptococcus
Beta-hemolytic colonies from throat culture should be tested with bacitracin (Group A Strep is susceptible, most other groups are resistant) or PYR test (Group A Strep is positive) for presumptive identification. Serological Lancefield grouping (latex agglutination) provides definitive group identification. Group A Strep is the primary throat pathogen requiring treatment.
What precautions must be taken when processing specimens suspected of containing Mycobacterium tuberculosis?
Answer: Processing in a certified biological safety cabinet (BSC) with appropriate PPE in a containment level 2 laboratory
M. tuberculosis is transmitted by aerosol and poses an occupational risk. All specimen processing must be performed in a certified Class II biological safety cabinet (BSC) in a containment level 2 laboratory with appropriate PPE. Culture of M. tuberculosis may require containment level 3. Staff should be included in TB surveillance programs.
A CSF specimen has elevated protein, low glucose, elevated WBC with neutrophil predominance, and the Gram stain shows gram-negative diplococci. What is the most likely pathogen?
Answer: Neisseria meningitidis
Gram-negative diplococci (kidney-bean shaped) in CSF with a bacterial meningitis profile (high protein, low glucose, neutrophilic pleocytosis) is classic for Neisseria meningitidis. This is a medical emergency requiring immediate ceftriaxone therapy and close contact prophylaxis with rifampin or ciprofloxacin. It is reportable to public health.
What is the significance of extended incubation (up to 14 days) for blood cultures from patients with suspected endocarditis?
Answer: Some endocarditis pathogens (HACEK group, Brucella) are slow-growing and may not be detected in standard 5-day incubation
HACEK organisms (Haemophilus, Aggregatibacter, Cardiobacterium, Eikenella, Kingella) and other fastidious endocarditis pathogens may require extended incubation (up to 14 days) for detection. Modern automated systems detect most pathogens within 5 days, but the microbiology laboratory should be notified of suspected endocarditis to ensure appropriate incubation.
A stool culture yields a non-lactose fermenting, H2S-positive organism on Hektoen enteric agar. What is the most likely identification?
Answer: Salmonella species
On Hektoen enteric agar, Salmonella appears as blue-green colonies with black centers (H2S production). Salmonella does not ferment lactose or sucrose. Shigella appears similar but does not produce H2S. Further biochemical testing and serotyping are required for complete identification. Salmonella is reportable to public health.
What is the appropriate response when a laboratory identifies Neisseria meningitidis from a clinical specimen?
Answer: Immediately notify the physician and public health for contact prophylaxis
N. meningitidis isolation from any normally sterile site (blood, CSF) requires immediate physician notification and public health reporting. Close contacts need chemoprophylaxis (rifampin, ciprofloxacin, or ceftriaxone) within 24 hours to prevent secondary cases. This is a reportable disease in all Canadian jurisdictions.