CSMLS Clinical Microbiology Techniques Questions and Answers

Question 1

A clinical microbiology laboratory adopts MALDI-TOF MS for routine bacterial identification. What is the underlying principle of this technology?

Accepted Answer

Analysis of ribosomal protein profiles by mass spectrometry

Answer

Detection of specific nucleic acid sequences using fluorescent probes

Answer

Measurement of enzymatic activity through colorimetric substrate changes

Answer

Determination of fatty acid methyl esters (FAME) by gas chromatography

Question 2

A laboratory in Alberta is following a common two-step algorithm for the diagnosis of Clostridioides difficile infection (CDI) from a stool sample. The first step is a screening test for Glutamate Dehydrogenase (GDH) antigen, which is positive. What is the most appropriate second step to confirm active, toxin-producing CDI?

Accepted Answer

Perform a nucleic acid amplification test (NAAT) for the toxin B gene (tcdB)

Answer

Perform a cell culture cytotoxicity assay

Answer

Repeat the GDH antigen test on a new sample

Answer

Culture the organism on cycloserine-cefoxitin-fructose agar (CCFA)

Question 3

A medical laboratory technologist performs a Modified Hodge Test (MHT) to screen for carbapenemase production in a Klebsiella pneumoniae isolate. A distinct 'cloverleaf-like' pattern of indented growth of the indicator organism (E. coli ATCC 25922) is observed around the test streak. How should this result be interpreted?

Accepted Answer

The isolate is positive for carbapenemase production

Answer

The test is invalid due to over-inoculation of the indicator strain

Answer

The isolate is negative for carbapenemase production

Answer

The isolate possesses an AmpC beta-lactamase but not a carbapenemase

Question 4

According to Clinical and Laboratory Standards Institute (CLSI) guidelines, which are broadly followed in Canada for antimicrobial susceptibility testing (AST), what is the primary purpose of performing quality control using ATCC reference strains?

Accepted Answer

To monitor the precision and accuracy of the test procedure

Answer

To verify that patient isolates are correctly identified before testing

Answer

To ensure the antimicrobial agents have not expired

Answer

To determine the minimum inhibitory concentration (MIC) for new antibiotics

Question 5

A technologist receives a cerebrospinal fluid (CSF) specimen in the microbiology lab from a suspected case of bacterial meningitis. The specimen is received at 3:00 PM and the Gram stain is performed immediately. The day shift ends at 4:00 PM. Which of the following actions is most critical regarding the culture of this specimen?

Accepted Answer

Immediately inoculate the specimen onto appropriate media, such as Chocolate and Blood agar, and place in a CO2 incubator.

Answer

Inoculate the culture plates and leave them at room temperature for the evening shift to incubate.

Answer

Refrigerate the specimen at 4°C until the next morning to ensure a fresh subculture.

Answer

Perform an antigen detection test and wait for the results before setting up the culture.

Question 6

Which of the following is the most appropriate method for sterilizing a heat-sensitive solution containing antibiotics for use in culture media?

Accepted Answer

Filtration through a 0.22 µm pore size membrane

Answer

Autoclaving at 121°C for 15 minutes

Answer

Exposure to ultraviolet (UV) radiation for 30 minutes

Answer

Boiling at 100°C for 10 minutes