lecture7 Flashcards
1
Q
- 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
A
(A) Capsule
2
Q
- 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.
A
(D) Antibody to the M protein of Streptococcus pyogenes crossreacts with cardiac muscle and damages it.
3
Q
- Which one of following laboratory tests is the most appropriate to distinguish Streptococcus pyogenes from other β-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
A
(D) Inhibition by bacitracin
4
Q
- 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
A
(E) Streptococcus pyogenes
5
Q
- 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
β-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.
A
(E) Streptococcus pyogenes.
6
Q
- 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
A
(B) Staphylococcus saprophyticus and Enterococcus faecalis
7
Q
- 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, has 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 β-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
A
(B) Streptococcus agalactiae
8
Q
15. 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
A
(D) Penicillin G or levofloxacin
9
Q
- 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
A
(E) Penicillin G and gentamicin
10
Q
- 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, coagulasepositive
(B) Gram-positive cocci in chains, catalase-negative, coagulasenegative
(C) Gram-positive cocci in clusters, catalase-positive, coagulasenegative
(D) Gram-positive cocci in clusters, catalase-negative, coagulasepositive
(E) Gram-positive diplococci, catalase-negative, coagulase-positive
A
(C) Gram-positive cocci in clusters, catalase-positive, coagulase-negative
11
Q
- 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
A
(D) Protein A
12
Q
- The main reason why methicillin-resistant Staphylococcus
aureus (MRSA) strains are resistant to methicillin and nafcillin
is:
(A) they produce β-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.
A
(B) they have altered penicillin-binding proteins that have reduced binding of the antibiotics.
13
Q
- 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.
A
(D) P-V leukocidin.
14
Q
6. 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
A
(E) Vancomycin
15
Q
2. 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
A
(E) Toxic shock syndrome
