FREE AP-MICRO Bacteriology: Gram-Positive Identification Questions and Answers

Question 1

A Gram-positive coccus isolated from a urine culture is catalase-positive and coagulase-negative.
Which of the following tests would be most appropriate to differentiate Staphylococcus saprophyticus from other coagulase-negative staphylococci?

Accepted Answer

Novobiocin susceptibility

Answer

Bacitracin susceptibility

Answer

Bile esculin hydrolysis

Answer

CAMP test

Question 2

A laboratory technologist is working on the identification of an alpha-hemolytic, Gram-positive coccus isolated from a sputum culture. Which of the following test results would presumptively identify the organism as Streptococcus pneumoniae?

Accepted Answer

Susceptibility to optochin (P disk)

Answer

Susceptibility to bacitracin (A disk)

Answer

Positive bile esculin test

Answer

Positive CAMP test

Question 3

A beta-hemolytic, Gram-positive coccus is isolated from a throat swab. The organism is catalase-negative. Which single rapid test provides the most definitive presumptive identification of Streptococcus pyogenes (Group A Streptococcus)?

Accepted Answer

PYR (pyrrolidonyl arylamidase) test

Answer

Coagulase test

Answer

Bile solubility test

Answer

Growth in 6.5% NaCl

Question 4

A technologist observes an arrowhead-shaped zone of enhanced hemolysis at the junction where a beta-hemolytic Streptococcus is streaked perpendicular to a Staphylococcus aureus streak on a sheep blood agar plate. This phenomenon is characteristic of which organism?

Accepted Answer

Streptococcus agalactiae

Answer

Streptococcus pneumoniae

Answer

Enterococcus faecalis

Answer

Streptococcus pyogenes

Question 5

A Gram-positive coccus growing in chains is isolated from a blood culture. The organism is catalase-negative, does not produce hemolysis on sheep blood agar (gamma-hemolytic), and grows in 6.5% NaCl broth. It also hydrolyzes esculin in the presence of bile. Which of the following is the most likely identification?

Accepted Answer

Enterococcus faecalis

Answer

Staphylococcus aureus

Answer

Streptococcus bovis

Answer

Streptococcus pneumoniae

Question 6

Which of the following biochemical tests is based on the principle that an organism can hydrolyze esculin to esculetin in the presence of bile, with the resulting esculetin reacting with ferric citrate to form a dark brown or black precipitate?

Accepted Answer

Bile esculin test

Answer

Catalase test

Answer

Coagulase test

Answer

Optochin susceptibility test