MLPAO Microbiology and Parasitology Clinical Applications

Question 1

A Gram stain of a positive blood culture shows gram-positive cocci in clusters. What organism is most likely and what empiric therapy should be communicated?

Accepted Answer

Staphylococcus species; vancomycin pending identification and susceptibilities

Answer

Gram-positive cocci in clusters from blood culture is most consistent with Staphylococcus species. Because MRSA must be considered, empiric vancomycin is recommended until species identification and susceptibility results are available. If methicillin-susceptible S. aureus (MSSA) is confirmed, therapy is narrowed to cloxacillin/cefazolin.

Question 2

A urine culture grows more than 100,000 CFU/mL of a single organism. What does this indicate?

Accepted Answer

Significant bacteriuria consistent with urinary tract infection

Answer

Growth of ≥10⁵ CFU/mL (100,000 CFU/mL) of a single organism from a clean-catch midstream urine is considered significant bacteriuria. This threshold, combined with clinical symptoms, supports the diagnosis of UTI. Lower counts may be significant in catheterized specimens or symptomatic patients.

Question 3

A laboratory identifies a Salmonella species from a stool culture. What is the reporting obligation in Canada?

Accepted Answer

Salmonella is a reportable/notifiable disease and must be reported to public health authorities

Answer

Salmonellosis is a reportable/notifiable disease in all Canadian provinces and territories. The laboratory must report the isolation to local public health authorities. Isolates may be sent to a reference laboratory for serotyping and molecular typing for outbreak investigation and surveillance purposes.

Question 4

Which infection control precaution is implemented when Clostridioides difficile infection is suspected?

Accepted Answer

Contact precautions with hand washing using soap and water (not alcohol-based hand rub)

Answer

C. difficile requires contact precautions including gown and gloves, with hand hygiene using soap and water. Alcohol-based hand sanitizers do NOT kill C. difficile spores. Enhanced environmental cleaning with sporicidal agents (dilute bleach) is also essential as spores can persist on surfaces for months.

Question 5

A wound culture grows a beta-hemolytic, catalase-negative, gram-positive coccus that is PYR-positive. What is the most likely identification?

Accepted Answer

Group A Streptococcus (Streptococcus pyogenes)

Answer

The key features are: beta-hemolytic (GAS, GBS, or Group C/G), catalase-negative (streptococcus/enterococcus, not staphylococcus), gram-positive cocci, and PYR-positive. Among beta-hemolytic streptococci, Group A Streptococcus (S. pyogenes) is PYR-positive while Group B and other groups are PYR-negative.

MLPAO - Medical Laboratory Professionals Association of Ontario Practice Test

MLPAO - Medical Laboratory Professionals Association of Ontario Practice Test

MLPAO Microbiology and Parasitology Clinical Applications