CSMLS - Canadian Society for Medical Laboratory Science Microbiology: Gram-Positive Cocci Identification Questions and Answers

Question 1

A medical laboratory technologist is analyzing a culture from a urine sample of a 22-year-old female patient with symptoms of a urinary tract infection.
The Gram stain reveals Gram-positive cocci in clusters.
The organism is catalase-positive and coagulase-negative.
Which of the following tests is most crucial for the presumptive identification of Staphylococcus saprophyticus?

Accepted Answer

Novobiocin susceptibility

Answer

Bacitracin susceptibility

Answer

Bile esculin hydrolysis

Answer

PYR (pyrrolidonyl arylamidase) test

Question 2

An alpha-hemolytic, catalase-negative, Gram-positive coccus is isolated from a sputum culture. The colonies are mucoid and demonstrate a zone of inhibition of 16 mm around a 5 µg optochin disk. What is the most likely identification of this organism?

Accepted Answer

Streptococcus pneumoniae

Answer

Streptococcus agalactiae

Answer

Enterococcus faecalis

Answer

Streptococcus pyogenes

Question 3

A technologist performs a CAMP test to identify a beta-hemolytic Streptococcus isolated from a neonatal blood culture. An arrowhead-shaped zone of enhanced hemolysis is observed where the isolate meets the streak of *Staphylococcus aureus*. This result is indicative of which organism?

Accepted Answer

Streptococcus agalactiae (Group B)

Answer

Streptococcus pyogenes (Group A)

Answer

Streptococcus bovis (Group D)

Answer

Staphylococcus aureus

Question 4

Which of the following Gram-positive cocci is a key pathogen known for being catalase-positive, coagulase-positive, and often beta-hemolytic on blood agar?

Accepted Answer

Staphylococcus aureus

Answer

Staphylococcus epidermidis

Answer

Streptococcus pyogenes

Answer

Enterococcus faecium

Question 5

A Gram-positive coccus, growing in chains, is isolated from a throat swab. It is beta-hemolytic and catalase-negative. A rapid PYR test is performed and yields a bright cherry-red color. Which organism is most likely present?

Accepted Answer

Streptococcus pyogenes

Answer

Streptococcus agalactiae

Answer

Streptococcus pneumoniae

Answer

Staphylococcus saprophyticus

Question 6

An isolate from a wound infection shows Gram-positive cocci in pairs and chains. The organism is catalase-negative and grows on bile esculin agar, turning the slant black. It also demonstrates growth in 6.5% NaCl broth. What is the most probable identification?

Accepted Answer

Enterococcus faecalis

Answer

Streptococcus bovis group

Answer

Streptococcus pyogenes

Answer

Streptococcus agalactiae