Question 1

A 36-year-old man presents with focal central nervous system signs. Imaging shows a brain abscess. The dominant organism is an anaerobe normally found as part of the oral flora. Which of the following best fits that description?

A) Nocardia
B)Actinomyces
C)Mycobacterium
D)Pseudomonas aeruginosa

Actinomyces

Accepted Answer

Only Actinomyces is anaerobic; the rest are aerobic. (And, of those mentioned, only Actinomyces is part of the normal oral flora. Nocardia can, however, cause brain abscesses as well, but it is acquired from the environment.)

Question 2

A 23-year-old man who has recently started working on a sheep farm in Nova Scotia develops pneumonia shortly after helping with lambing. His cough produces little sputum, and a saline-induced sputum sample shows no predominant organism either with Gram stain or with acid-fast stain. It is established that he acquired the pneumonia from parturition products from the sheep. Which agent is most likely to be the cause of his pneumonia?

A) Rickettsia akari
B)Rickettsia typhi
C)Rickettsia rickettsii
D)Coxiella burnetii
E)Anaplasma phagocytophilum

Coxiella burnetii

Accepted Answer

Coxiella burnetii is a rickettsia-like organism that can be spread via amniotic fluid, aerosols, or dust particles. It withstands drying and thus can be transmitted at least 10 miles by the wind.

Question 3

A 3-year-old girl presents with difficulty breathing and will not lie down to be examined. You suspect acute bacterial epiglottitis and examine the child's epiglottis, which is highly inflamed. Which vaccine are you most likely to find that the child is missing?

A) Diphtheria
B)Neisseria meningitidis
C)Polio
D)Streptococcus pneumoniae (conjugate vaccine)
E)Haemophilus influenzae

Haemophilus influenzae

Accepted Answer

Epiglottitis is a medical emergency requiring hospitalization. It can be fatal in 24 hours. Pediatric cases were almost always caused by H. influenzae type b and have been dramatically reduced by the conjugate vaccine.

Question 4

A 22-year-old man with cystic fibrosis presents with fever and increasing dyspnea. A Gram-negative organism is found in unusually high numbers in the pulmonary mucus. Which virulence factor is most important in colonization and maintenance of the organism in the lungs?

A) Exotoxin A
B)Pyocyanin (blue-green pigment)
C)Polysaccharide slime
D)Endotoxin

Accepted Answer

Staphylococcus aureus and Pseudomonas aeruginosa are two primary pulmonary colonizers that cause pneumonia in patients with cystic fibrosis. (Staphylococcus is usually only in young CF patients.) Of the two, Pseudomonas is Gram-negative. Its slime material (alginate) produces the resistance to phagocytic killing and poor penetration of antibiotics to the site, which, in conjunction with the antibiotic resistance of Pseudomonas, make these serious infections.

Question 5

From the above case, exotoxin A of the causative agent most closely resembles the action of which other microbial toxin?&#10;A) Heat-labile toxin (LT) of Escherichia coli&#10;B)Shiga toxin&#10;C)Diphtheria toxin&#10;D)Vibrio cholerae toxin&#10;E)Verotoxin

Accepted Answer

Both Pseudomonas exotoxin A and diphtheria toxin inhibit protein synthesis through the inhibition of elongation factor (EF-2). Incorrect choices include: Shiga toxin, which is a cytotoxin, enterotoxin, and neurotoxin. Vibrio cholerae enterotoxin and E. coli labile toxin (LT) both result in increased cyclic adenosine monophosphate (cAMP).

Question 6

A 36-year-old man who immigrated to the United States 15 years ago and lived in a crowded resettlement camp before coming to the United States presents with a cough that has been bothering him for several weeks. He has also lost 10 pounds. A gamma interferon release blood test is positive. Which of the following factors is known to be most important in triggering the granulomatous reaction to wall off and contain the infection?

A) Cord factor
B)Mycolic acid
C)Purified protein derivative (PPD)
D)Sulfatides
E)Wax D

Accepted Answer

Mtb's cord factor helps trigger the Th1 response, which helps contain the infection.

Question 7

A 75-year-old patient develops diarrhea 5 days after starting antibiotic treatment for a serious staphylococcal infection. What is the most likely causative agent?&#10;A) Clostridium perfringens&#10;B)Clostridium difficile&#10;C)Pseudomonas aeruginosa&#10;D)Shigella sonnei

Accepted Answer

Clostridium difficile has been shown to be the major causative agent of pseudomembranous colitis, which causes diarrhea that most commonly starts after 3 to 4 days of antibiotic administration.

Question 8

A 23-year-old woman presents with mild gastroenteritis a few days after having a variety of sushi at a party. There is no blood or pus in the stool. Which causative agent is most likely to have caused this illness?

A) Vibrio cholerae
B)Vibrio parahaemolyticus
C)Salmonella typhi
D)Shigella sonnei

Accepted Answer

Vibrio cholerae causes classic cholera, which is not generally mild or selflimited; Vibrio parahaemolyticus, in contrast, causes a relatively mild gastroenteritis. It is also found in raw fish. Sal. typhi is the causative agent of typhoid. Shigellae infections are always invasive and generally will have a little pus in the stool.

Question 9

Yersinia pestis may be transferred by&#10;A) Dermacentor tick bite&#10;B)Human body louse bite&#10;C)Ixodes tick bite&#10;D)Respiratory droplets

Accepted Answer

Most transmission in the United States is from an infected flea bite (a choice not given in the question). The other route of transmission is through respiratory droplets from patients who have developed pneumonic emboli and pneumonia.

Question 10

A patient who had surgery to put in a pacemaker and who states he felt fine for the first 2 months now presents 3 months postoperatively with complaints of malaise and increasing fatigue. He is running a low-grade fever, tires easily, and has worsening heart murmurs. Which of the following staphylococcal organisms causes subacute bacterial endocarditis that generally occurs 2 months or more after heart surgery?

A) Staphylococcus aureus
B)Staphylococcus epidermidis
C)Staphylococcus haemolyticus
D)Staphylococcus saprophyticus

Accepted Answer

Staphylococcus epidermidis is ubiquitous as part of the normal flora. Organisms are introduced into the host during invasive procedures. Staph. aureus is more likely to be acute, with high fever and damage developing more quickly.

Question 11

A previously healthy 6-month-old boy presents with upper body weakness. He cannot hold his eyes open, pupils do not react, and he cannot hold his head up. What is the proper treatment?&#10;A) Send him home on amoxicillin and clindamycin (to stop the toxin production quickly)&#10;B)Give him a dose of equine anti-botulinum immunoglobulin&#10;C)Offer monitored supportive care with antibiotics and human anti-botulinum immunoglobulin&#10;D)Offer monitored supportive care with human anti-botulinum immunoglobulin&#10;E)Offer monitored supportive care with no antibiotics and no antitoxin

Accepted Answer

The answer of A previously healthy 6-month-old boy presents with...

Question 12

A 78-year-old man presents with a high fever, cough producing a blood-tinged sputum, and difficulty breathing. Sputum shows an organism consistent with Streptococcus pneumoniae. What is the most important virulence factor?

A) Endotoxin
B)A phospholipase allowing Streptococcus pneumoniae to escape the phagosome quickly
C)Polypeptide capsule
D)Polysaccharide capsule

Accepted Answer

The answer of A 78-year-old man presents with a high...

Question 13

Which of the following organisms grows in 40% bile?&#10;A) Enterococcus faecalis&#10;B)Streptococcus pneumoniae&#10;C)Group B streptococci&#10;D)Viridans streptococci

Accepted Answer

The answer of Which of the following organisms grows in...

Question 14

A 45-year-old man who recently returned from Africa has been febrile for several days and now presents with abdominal pain. His blood cultures grow out Salmonella typhi. What was the most likely source of his infection?

A) Raw chicken
B)Undercooked hamburger
C)Contact with baby goats on a farm and then eating without washing hands
D)A food preparer with bad personal hygiene
E)Undercooked pork

Accepted Answer

The answer of A 45-year-old man who recently returned from...

Question 15

A 4-day-old infant girl now showing signs of sepsis is brought to the emergency department. She was preterm (33 weeks) and born at home to her 16-year-old mom after 22 hours of labor following the rupture of the membranes. A friend helped the mother deliver the baby. What is the best description for the agent most likely causing the sepsis if it was acquired during labor but prior to delivery? All organisms in the answer choices are Gram-positive, catalasenegative cocci found in pairs or short chains.

A) Nonhemolytic organisms found as part of the normal fecal flora; resistant to bile and optochin; carries a high level of drug resistance
B)Alpha-hemolytic diplococci sensitive to both bile and optochin
C)Beta-hemolytic cocci in chains and carrying Lancefield's Group B antigen
D)Alpha-hemolytic cocci in chains; resistant to bile and optochin

Accepted Answer

The answer of A 4-day-old infant girl now showing signs...

Question 16

A 62-year-old woman presents with signs of a gastric ulcer. She does not regularly take nonsteroidal anti-inflammatory agents. Which characteristic appears to play a central role in the organism's ability to survive transit of the lumen to colonize the stomach?

A) Phospholipase-C production
B)Urease production
C)Microaerophilic lifestyle
D)O antigens

Accepted Answer

The answer of A 62-year-old woman presents with signs of...

Question 17

A 54-year-old man develops a pyogenic infection along the suture line after knee surgery. The laboratory gives a preliminary report of a beta-hemolytic, catalase-positive, coagulase-positive, Grampositive coccus. The most likely causative agent is

A) Moraxella catarrhalis
B)Staphylococcus aureus
C)Staphylococcus epidermidis
D)Streptococcus agalactiae
E)Streptococcus pyogenes

Accepted Answer

The answer of A 54-year-old man develops a pyogenic infection...

Deck 4: Bacterial Diseases