CMT Microbiology 2

Question 1

A catalase-positive, coagulase-negative staphylococcus from a young woman's urine is resistant to novobiocin. What is the most likely identification?

Accepted Answer

Staphylococcus saprophyticus

Answer

S. saprophyticus is the novobiocin-resistant CoNS associated with UTIs in young women.

Question 2

A beta-hemolytic, catalase-negative coccus from a vaginal/rectal swab is CAMP positive and hippurate hydrolysis positive. Which organism is it?

Accepted Answer

Streptococcus agalactiae

Answer

Group B Streptococcus (S. agalactiae) is CAMP positive and hydrolyzes hippurate.

Question 3

Which combination of results presumptively identifies Streptococcus pyogenes?

Accepted Answer

PYR positive, bacitracin susceptible

Answer

Group A strep is PYR positive and susceptible to bacitracin (A disk).

Question 4

An alpha-hemolytic, catalase-negative, lancet-shaped diplococcus is optochin susceptible. Which additional test confirms the identification?

Accepted Answer

Bile solubility

Answer

S. pneumoniae is lysed by bile (sodium deoxycholate), distinguishing it from viridans streptococci.

Question 5

A catalase-negative gram-positive coccus hydrolyzes esculin in the presence of bile and grows in 6.5% NaCl. What is the presumptive genus?

Accepted Answer

Enterococcus

Answer

Enterococcus is bile esculin positive and salt tolerant, while S. bovis group fails to grow in 6.5% NaCl.

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