Exam 2- (CH 15) Streptococcus, Enterococcus, and other catalase-negative, gram-positive cocci Review Questions

Question 1

Points to Remember

■ The organisms included in the family Streptococcaceae and the Streptococcus-like organisms are gram-positive cocci usually arranged in pairs or chains that are catalase-negative.
■ Hemolysis on sheep blood agar is often a starting point for the identification of streptococci and similar organisms.
■ Many streptococci can be categorized based on Lancefield group antigens

Answer 1

■ Key tests for the identification of streptococci and similar organisms include the bacitracin susceptibility, Christie, Atkins, and Munch-Petersen (CAMP), hippurate hydrolysis, pyrrolidonyl-α-naphthylamide (PYR) hydrolysis, leucine aminopeptidase (LAP), Voges-Proskauer (VP), β-D-glucuronidase, bile esculin, salt tolerance, optochin susceptibility, and bile solubility tests.
■ Many clinical microbiology laboratories use group antigen detection to identify the streptococci.

Question 2

Points to Remember

■ Group A streptococci are important pathogens that cause acute bacterial pharyngitis, skin and soft tissue infections, and invasive infections, including necrotizing fasciitis.
■ Emerging resistance of Streptococcus pneumoniae to numerous antimicrobials is becoming a major health concern.
■ Viridans streptococci, although usually nonpathogenic, can cause bacteremias, abscesses, and oral infections such as gingivitis and dental caries.
■ Nutritionally variant streptococci are classified within the genera Granulicatella and Abiotrophia.

Answer 2

■ Enterococci cause approximately 5% to 10% of infections in patients with bacterial endocarditis.
■ Streptococcus agalactiae is a significant cause of invasive disease in newborns.
■ Group C and G streptococci are important human pathogens associated with infections such as endocarditis, meningitis, primary bacteremia, necrotizing fasciitis, and myositis.

Question 3

Which Streptococcus virulence factor is responsible for hemolysis on sheep blood agar (SBA) incubated aerobically?
A. Streptolysin S
B. Hyaluronidase
C. Streptolysin O
D. Protein M

Answer 3

A. Streptolysin S

Question 4

Rheumatic fever typically follows
A. Streptococcus pyogenes pharyngitis.
B. toxic shock syndrome.
C. necrotizing fasciitis.
D. Streptococcus agalactiae mastitis.

Answer 4

A. Streptococcus pyogenes pharyngitis

Question 5

3. It is recommended that all pregnant women be screened for group B streptococcus (GBS) at _____ weeks’ gestation.
   A. 15 to 20
   B. 22 to 24
   C. 30 to 32
   D. 35 to 37

Answer 5

D. 35 to 37

Question 6

Streptococcus agalactiae typically exhibits this type of hemolysis.
A. Alpha
B. Beta
C. Gamma
D. Delta

Answer 6

B. Beta

Question 7

Streptococcus pneumoniae is sensitive to this antibiotic which helps differentiate it from other α-hemolytic species.
A. Bacitracin
B. Amoxicillin
C. Methicillin
D. Optochin

Answer 7

D. Optochin

Question 8

The _______ group and the enterococci possess the group D antigen.
A. Streptococcus bovis
B. Streptococcus mitis
C. Streptococcus mutans
D. Streptococcus anginosus

Answer 8

A. Streptococcus bovis

Question 9

Enterococcus faecalis produces a two-subunit toxin called
A. teicoplanin.
B. VanE.
C. cytolysin.
D. Shiga toxin.

Answer 9

C. cytolysin.

Question 10

Which vancomycin-resistant Enterococcus phenotype is carried on a transposon (Tn1546) and characterized by high-level resistance to vancomycin and teicoplanin?
A. VanA
B. VanB
C. VanD
D. VanM

Answer 10

A. VanA

Question 11

Aerococci resemble this genus microscopically due to their typical arrangement patterns.
A. Streptococci
B. Staphylococci
C. Escherichia
D. Enterococcus

Answer 11

B. Staphylococci

Question 12

The Christie, Atkins, and Munch-Petersen (CAMP) test uses a β-lysin producing strain of
A. Streptococcus pyogenes.
B. Streptococcus pneumoniae.
C. Staphylococcus aureus.
D. Staphylococcus epidermidis.

Answer 12

C. Staphylococcus aureus.

Question 13

The bile solubility test takes advantage of the Streptococcus pneumoniae autocatalytic enzyme
A. amidase.
B. proteinase.
C. protein M.
D. cytolysin.

Answer 13

A. amidase.

Question 14

Name three tests that could be performed to aid in the identification of Streptococcus pyogenes.

Answer 14

Tests that would be useful in the identification of group A Streptococcus (S. pyogenes) are PYR (positive), bacitracin susceptibility (sensitive), and SXT susceptibility (resistant) tests, and an immunoassay for detection of the group A antigen.

Question 15

A β-hemolytic, catalase-negative, gram-positive coccus is found to be resistant to bacitracin and sulfamethoxazole. Which of the following is a likely presumptive identification?
a. Group A streptococci
b. Group B streptococci
c. Group D streptococci
d. Enterococci

Answer 15

b. Group B streptococci

Question 16

The Christie, Atkins, and Munch-Petersen (CAMP) test is based on enhanced hemolysis between CAMP factor and β-lysin from:
a. Streptococcus agalactiae
b. Staphylococcus epidermidis
c. Staphylococcus aureus
d. Enterococcus

Answer 16

c. Staphylococcus aureus

Question 17

A nonhemolytic, catalase-negative, gram-positive coccus is pyrrolidonyl α-naphthylamide (PYR)-positive. You should also expect the isolate to be:
a. Bile esculin-positive
b. Salt (6.5%) tolerant
c. Bile soluble
d. Both a and b

Answer 17

d. Both a and b

Question 18

The optochin test is most valuable in the identification of:
a. α-Hemolytic streptococci
b. β-Hemolytic streptococci
c. Nonhemolytic streptococci
d. Both a and b

Answer 18

a. α-Hemolytic streptococci

Question 19

What antimicrobial agent or agents are most commonly used to treat infections caused by pyogenic streptococci?

Answer 19

Penicillin is the drug of choice for the treatment of S. pyogenes pharyngitis. Patients allergic to penicillin are often treated with erythromycin.

Question 20

Streptococcus pyogenes has been associated with what invasive infections?

Answer 20

S. pyogenes has been linked to necrotizing fasciitis. Streptococcal toxic shock syndrome is a systemic disease mediated by a soluble toxin. The infective agent in this case is not necessarily invasive. Rheumatic fever and acute glomerulonephritis are immunologic sequelae and not invasive infections.

Question 21

Which streptococcal species is the most common cause of community-acquired bacterial pneumonia?

Answer 21

S. pneumoniae is the most common cause of community-acquired pneumonia and of bacterial pneumonia.

Question 22

What is the clinical significance of group B streptococci isolated from a vaginal culture of a pregnant woman?

Answer 22

Group B streptococci (S. agalactiae) are rarely associated with disease in healthy adults; however, they are a significant cause of morbidity and mortality in neonates. Neonates can acquire infection in utero following premature rupture of the membranes or during delivery. Pregnant women are often screened for group B streptococci as part of the prenatal workup.

Question 23

How would you recover nutritionally variant streptococci from clinical samples such as blood?

Answer 23

Members of the genera Granulicatella and Abiotrophia, formerly referred to as the nutritionally variant streptococci, have a requirement for pyridoxal. Isolates are generally able to grow in blood cultures but, to sustain growth on solid media, agar needs to be supplemented with pyridoxal. Alternatively, the bacteria can grow as small pinpoint colonies around colonies of Staphylococcus aureus, which secretes small amounts of pyridoxal during growth.