MLPAO Microbiology and Parasitology Diagnostic Methods

Question 1

What is the principle of the latex agglutination test used in microbiology?

Accepted Answer

Latex particles coated with antibodies agglutinate in the presence of target antigen

Answer

Latex agglutination tests use latex particles coated with specific antibodies. When mixed with a specimen containing the target antigen, the antibody-coated particles cross-link, forming visible agglutination. This rapid technique is used for identifying organisms (e.g., Cryptococcus, Group B Strep) and detecting antigens in CSF and other fluids.

Question 2

Which molecular method is the gold standard for detecting Chlamydia trachomatis and Neisseria gonorrhoeae?

Accepted Answer

Nucleic acid amplification test (NAAT)

Answer

NAAT (nucleic acid amplification test) is the gold standard for detecting C. trachomatis and N. gonorrhoeae due to its superior sensitivity and specificity. It can be performed on urine, endocervical, urethral, pharyngeal, and rectal specimens. Culture is still needed for antimicrobial susceptibility testing of N. gonorrhoeae.

Question 3

What is the purpose of performing a Gram stain on cerebrospinal fluid (CSF)?

Accepted Answer

To rapidly identify the presence and morphology of bacteria for urgent empiric antibiotic selection

Answer

Gram stain of CSF provides rapid (minutes) preliminary identification of bacterial meningitis pathogens based on morphology: gram-positive diplococci (S. pneumoniae), gram-negative diplococci (N. meningitidis), or gram-positive rods (Listeria). This guides empiric antibiotic therapy before culture results are available.

Question 4

Which chromogenic medium is used for screening of MRSA in clinical laboratories?

Accepted Answer

CHROMagar MRSA or similar chromogenic MRSA medium

Answer

Chromogenic MRSA media contain cefoxitin (selecting for MRSA) and chromogenic substrates that produce distinctive coloured colonies (typically pink/mauve for S. aureus). These media provide rapid screening results (18-24 hours) for MRSA colonization, which is important for infection prevention and control programs.

Question 5

What is the India ink preparation used to detect?

Accepted Answer

Cryptococcus neoformans capsule in CSF

Answer

The India ink preparation is a negative staining technique that reveals the thick polysaccharide capsule of Cryptococcus neoformans in CSF. The ink particles are excluded by the capsule, creating a clear halo around the yeast cell against a dark background. The cryptococcal antigen test (CrAg) has largely replaced India ink due to higher sensitivity.

MLPAO - Medical Laboratory Professionals Association of Ontario Practice Test

MLPAO - Medical Laboratory Professionals Association of Ontario Practice Test

MLPAO Microbiology and Parasitology Diagnostic Methods