Deck 12: Staphylococcus, Micrococcus, and Similar Organisms

Question 1

A tube coagulase test was performed on catalase-positive,gram-positive cocci that were b-hemolytic and grew on mannitol salt agar.The tube was checked after overnight incubation and was negative.Which of the following statements explains this discrepancy?

A)A tube coagulase should not be performed on a catalase-positive organism.
B)A b-hemolytic colony,which is catalase positive and grows on mannitol salt,is normally coagulase negative.
C)The test should have been read in 1 to 4 hours in case any hemolysins are present.
D)No discrepancy is present;the results are accurate.

Answer 1

C
Some strains of S.aureus produce fibrinolysin,which will dissolve the clot after 4 hours of incubation at 35°C and may appear to be negative if allowed to incubate longer than 4 hours.

Question 2

The tube coagulase test:

A)detects bound coagulase.
B)detects extracellular coagulase.
C)is performed on slide coagulase-positive isolates to confirm a positive result.
D)requires citrated reagent plasma.

Answer 2

B
The tube coagulase test is a test for the form of coagulase produced by S.aureus that is called extracellular free coagulase.

Question 3

The species of Staphylococcus,which is one of the most important human pathogens,is:

A)S.lentus.
B)Staphylococcus aureus.
C)S.mucilaginosus.
D)Staphylococcus intermedius.

Answer 3

B
A wide spectrum of factors,not all of which are completely understood,contribute to this organism's ability to cause infections and disease.Several toxins and enzymes mediate tissue invasion and survival at the infection site.

Question 4

Which organism is catalase positive,coagulase negative,pyrrolidonyl arylamidase (PYR)positive,susceptible to novobiocin,urease negative,and b-hemolytic on sheep blood agar?

A)S.epidermidis
B)S.saprophyticus
C)S.cohnii
D)S.haemolyticus

Question 5

Which of the following methods combines nucleic acid amplification testing and mass spectrometry (MS)for identification of S.aureus and MRSA?

A)Serodiagnosis
B)CHROMagar
C)The Xpert MRSA/SA test
D)PCR/ESI-MS

Question 6

The slide coagulase test is a rapid screening test for the production of:

A)clumping factor.
B)free coagulase.
C)extracellular coagulase.
D)catalase.

Question 7

Quality control should be performed on which two organisms to determine the validity of the oxidase reagent?

A)S.aureus and S.epidermidis
B)S.epidermidis and Enterococcus
C)Aerococcus and Enterococcus
D)Micrococcus and Aerococcus

Question 8

The most frequent agent of nosocomial bacteremia is:

A)catalase-negative micrococci.
B)coagulase-positive staphylococci.
C)catalase-negative stomatococci.
D)coagulase-negative staphylococci.

Question 9

The first identification test performed on a clinical isolate of gram-positive,catalase-positive cocci would likely be the:

A)penicillin test.
B)Gram stain.
C)oxidase test.
D)coagulase test.

Question 10

In clinical isolates,the most likely identification of coagulase-positive,catalase-positive,gram-positive cocci that are penicillin resistant would be:

A)S.aureus.
B)S.intermedius.
C)Stomatococcus luteus.
D)Micrococcus aureus.

Question 11

An infected intravenous (IV)catheter tip grew out gram-positive cocci,which were catalase positive and coagulase negative.The zone size of the novobiocin disk measured 18 mm.The most likely organism causing infection is:

A)S.saprophyticus.
B)S.epidermidis.
C)S.hominis.
D)S.cohnii.

Question 12

Which virulent and important human pathogen can also be recovered from the nares,perineum,and other skin sites of healthy people,especially in the hospital setting?

A)Micrococcus luteus
B)S.intermedius
C)S.aureus
D)All Micrococcaceae

Question 13

Which group of bacteria is described as catalase positive and is gram-positive cocci that grow facultatively anaerobic and form grapelike clusters?

A)Neisseria
B)Rothia (stomatococci)
C)Staphylococcus
D)Micrococcus

Question 14

The resident human microbiota,staphylococcus,which is more likely to cause infections in compromised hosts such as patients with cancer,is:

A)Staphylococcus saprophyticus.
B)S.aureus.
C)S.epidermidis.
D)S.intermedius.

Question 15

The Staphylococcaceae staphylococcus that is more likely to cause uncomplicated urinary tract infections in nonhospitalized hosts,especially sexually active young women,is:

A)S.saprophyticus.
B)S.aureus.
C)S.epidermidis.
D)S.intermedius.

Question 16

Isolates of coagulase-negative Staphylococcus from urinary tract infections can be presumptively identified as S.saprophyticus on the basis of its:

A)penicillin susceptibility.
B)novobiocin resistance.
C)penicillin resistance.
D)novobiocin susceptibility.