C H A P T E R 15 Gram-Positive Cocci You’re in the clinical laboratory looking at a Gram stain when the laboratory technician comes up to you and says, “I think your patient has Staph epi [short for Staphylococcus epidermidis] bacteremia.” Which one of the following sets of results did the tech find with the organism recovered from the blood culture? (A) Gram-positive cocci in chains, catalase-positive, coagulase-positive (B) Gram-positive cocci in chains, catalase-negative, coagulase-negative (C) Gram-positive cocci in clusters, catalase-positive, coagulase-negative (D) Gram-positive cocci in clusters, catalase-negative, coagulase-positive

You’re in the clinical laboratory looking at a Gram stain when the

laboratory technician comes up to you and says, “I think your

patient has Staph epi [short for Staphylococcus epidermidis] bacteremia.”

Which one of the following sets of results did the tech

find with the organism recovered from the blood culture?

(A) Gram-positive cocci in chains, catalase-positive,

coagulase-positive

(B) Gram-positive cocci in chains, catalase-negative,

coagulase-negative

(C) Gram-positive cocci in clusters, catalase-positive,

coagulase-negative

(D) Gram-positive cocci in clusters, catalase-negative,

coagulase-positive

(E) Gram-positive diplococci, catalase-negative,

coagulase-positive

 

1. Superantigen production by Staphylococcus aureus is involved in

the pathogenesis of which one of the following diseases?

(A) Impetigo

(B) Osteomyelitis

(C) Scalded skin syndrome

(D) Septicemia

(E) Toxic shock syndrome

 

1. Which one of the following is the virulence factor produced by

Staphylococcus aureus that prevents the activation of complement

and thereby reduces opsonization by C3b?

(A) Catalase

(B) Coagulase

(C) Endotoxin

(D) Protein A

(E) Teichoic acid

 

1. The main reason why methicillin-resistant Staphylococcus aureus

(MRSA) strains are resistant to methicillin and nafcillin is:

(A) they produce -lactamase that degrades the antibiotics.

(B) they have altered penicillin-binding proteins that have

reduced binding of the antibiotics.

(C) they have mutant porin proteins that prevent the antibiotics

from entering the bacteria.

(D) they have plasmid-encoded export proteins that remove the

drug from the bacteria.

 

1. A pore-forming exotoxin produced by Staphylococcus aureus

that kills cells and is important in the severe, rapidly spreading

necrotizing lesions caused by MRSA strains is:

(A) coagulase.

(B) enterotoxin.

(C) exfoliatin.

(D) P-V leukocidin.

(E) staphyloxanthin.

 

1. Of the following antibiotics, which one is the most appropriate

to treat a severe necrotizing skin infection caused by an MRSA

strain of Staphylococcus aureus?

(A) Amoxicillin

(B) Ceftriaxone

(C) Ciprofloxacin

(D) Gentamicin

(E) Vancomycin

 

1. An outbreak of serious pneumococcal pneumonia and sepsis

among inmates in an overcrowded prison has occurred. Laboratory

analysis determined that one serotype was involved. The prison

physician said that the pneumococcal vaccine might have limited

the outbreak. Which one of the following structures of the pneumococcus

is responsible for determining the serotype and is also the

immunogen in the vaccine?

(A) Capsule

(B) Flagellar protein

(C) O antigen

(D) Peptidoglycan

(E) Pilus protein

 

1. Which one of the following best describes the pathogenesis of

rheumatic fever?

(A) An exotoxin produced by Streptococcus pyogenes that acts as a

superantigen damages cardiac muscle.

(B) An exotoxin produced by Streptococcus pyogenes that ADPribosylates

a G protein damages joint tissue.

(C) Antibody to the capsular polysaccharide of Streptococcus pyogenes

cross-reacts with joint tissue and damages it.

(D) Antibody to the M protein of Streptococcus pyogenes crossreacts

with cardiac muscle and damages it.

(E) Endotoxin produced by Streptococcus pyogenes activates macrophages

to release cytokines that damage cardiac muscle.

 

1. Which one of following laboratory tests is the most appropriate

to distinguish Streptococcus pyogenes from other -hemolytic

streptococci?

(A) Ability to grow in 6.5% NaCl

(B) Activation of C-reactive protein

(C) Hydrolysis of esculin in the presence of bile

(D) Inhibition by bacitracin

(E) Inhibition by optochin

1. Infections by which one of the following bacteria are typically

treated with penicillins such as amoxicillin, because they exhibit

neither low-level resistance nor high-level resistance and synergy

with an aminoglycoside is not required in order for penicillins to

be effective?

(A) Enterococcus faecalis

(B) Staphylococcus aureus

(C) Staphylococcus epidermidis

(D) Streptococcus pneumoniae

(E) Streptococcus pyogenes

 

1. Your patient in the emergency room has a 5-cm ulcer on her leg

that is surrounded by a red, warm, and tender area of inflammation.

You do a Gram stain on pus from the ulcer and see

gram-positive cocci in chains. Culture of the pus grows small

-hemolytic colonies that are catalase-negative and are inhibited

by bacitracin. These results indicate that the organism causing

her lesion is most likely:

(A) Enterococcus faecalis.

(B) Staphylococcus aureus.

(C) Streptococcus agalactiae.

(D) Streptococcus pneumoniae.

(E) Streptococcus pyogenes.

 

1. The Jones family of four had a delicious picnic lunch last Sunday.

It was a warm day, and the food sat in the sun for several hours.

Alas, 3 hours later, everyone came down with vomiting and nonbloody

diarrhea. In the emergency room, it was found that Mrs.

Jones, who prepared the food, had a paronychia on her thumb.

Which one of the following is the most likely causative organism?

(A) Enterococcus faecalis

(B) Staphylococcus aureus

(C) Staphylococcus epidermidis

(D) Streptococcus agalactiae

(E) Streptococcus pyogenes

 

1. A 20-year-old sexually active woman reports dysuria and other

symptoms of a urinary tract infection. Gram stain of the urine

reveals gram-positive cocci. Which one of the following sets of

bacteria is most likely to cause this infection?

(A) Staphylococcus aureus and Streptococcus pyogenes

(B) Staphylococcus saprophyticus and Enterococcus faecalis

(C) Streptococcus agalactiae and Staphylococcus epidermidis

(D) Streptococcus pneumoniae and Enterococcus faecalis

(E) Streptococcus pyogenes and Streptococcus pneumonia

 

1. Your patient is a 2-week-old infant who was well until 2 days ago,

when she stopped feeding and became irritable. She now has a

fever to 38°C, developed a petechial rash all over her body, and

is very difficult to arouse. In the emergency room, a blood culture

and a spinal tap were done. Gram stain of the spinal fluid

showed gram-positive cocci in chains. Culture of the spinal fluid

on blood agar revealed -hemolytic colonies that grew in the

presence of bacitracin and hydrolyzed hippurate. Which one of

the following is the most likely causative organism?

(A) Staphylococcus aureus

(B) Streptococcus agalactiae

(C) Streptococcus mutans

(D) Streptococcus pneumoniae

(E) Streptococcus pyogenes

 

1. Your patient is a 50-year-old woman who has a communityacquired

pneumonia caused by Streptococcus pneumoniae. Antibiotic

susceptibility tests reveal an MIC of less than 0.1 mg/mL

to penicillin G. Which one of the following is the best antibiotic

to treat the infection?

(A) Clindamycin

(B) Gentamicin

(C) Metronidazole or doxycycline

(D) Penicillin G or levofloxacin

(E) Vancomycin

 

1. Your patient is a 70-year-old man with endocarditis caused by

Enterococcus faecalis. Which one of the following is the best combination

of antibiotics to treat the infection?

(A) Azithromycin and trimethoprim-sulfamethoxazole

(B) Chloramphenicol and rifampin

(C) Doxycycline and levofloxacin

(D) Metronidazole and clindamycin

(E) Penicillin G and gentamicin