Question 1

Which of the following characteristics distinguishes Neisseria from many other Gram-negative pathogens?

Accepted Answer

They are oxidase positive.

Question 2

A patient presents with painful urination and purulent discharge. Gram-negative diplococci are observed in pus from the inflamed penis. Which organism is most likely responsible?

Accepted Answer

Neisseria gonorrhoeae

Question 3

Which virulence factor allows Neisseria gonorrhoeae to evade the immune system by cleaving secretory IgA?

Accepted Answer

Protease

Question 4

Which of the following is the most common cause of meningitis in individuals under 20 years of age?

Accepted Answer

Neisseria meningitidis

Question 5

A rapid oxidase test is performed on two unknown Gram-negative bacilli. One is oxidase positive and the other is oxidase negative. Which family does the oxidase negative organism most likely belong to?

Accepted Answer

Enterobacteriaceae

Question 6

Which of the following is a defining characteristic of coliform bacteria?

Accepted Answer

They rapidly ferment lactose to form gas.

Question 7

A 5-year-old child in a developing country presents with severe diarrhea, cramps, and vomiting. Laboratory tests reveal the presence of enterotoxigenic Escherichia coli (ETEC). Which virulence factor is most likely responsible for the symptoms?

Accepted Answer

Enterotoxins

Question 8

Which of the following is associated with the consumption of undercooked ground beef and can cause hemolytic uremic syndrome?

Accepted Answer

Escherichia coli O157:H7

Question 9

A hospital patient develops pneumonia and the causative agent is found to be a Gram-negative rod with a prominent capsule. Which organism is most likely responsible?

Accepted Answer

Klebsiella pneumoniae

Question 10

Which of the following bacteria is known for producing a red pigment when grown at room temperature and is often associated with hospital-acquired infections?

Accepted Answer

Serratia marcescens

Question 11

A patient with a long-term urinary catheter develops a urinary tract infection. The causative agent is a swarming, highly motile, Gram-negative rod. Which organism is most likely responsible?

Accepted Answer

Proteus mirabilis

Question 12

Which of the following is a true statement about Salmonella enterica serotype Typhi?

Accepted Answer

Humans are the only host.

Question 13

A child presents with severe dysentery after ingesting contaminated food. The causative agent is a nonmotile, oxidase-negative Gram-negative rod. Which organism is most likely responsible?

Accepted Answer

Shigella dysenteriae

Question 14

Which of the following is the natural host for Yersinia pestis, the causative agent of plague?

Accepted Answer

Rodents

Question 15

Which of the following is a common route of human infection with Pasteurella multocida?

Accepted Answer

Animal bites or inhalation of aerosols

Question 16

Which of the following statements about Haemophilus influenzae type b (Hib) is correct?

Accepted Answer

It was a common cause of meningitis in children before vaccination.

Question 17

Which of the following is a key difference between coliform and noncoliform Enterobacteriaceae?

Accepted Answer

Coliforms rapidly ferment lactose, noncoliforms do not.

Question 18

Which of the following is a major virulence factor shared by all truly pathogenic Enterobacteriaceae such as Salmonella, Shigella, and Yersinia?

Accepted Answer

Type III secretion system

Question 19

A laboratory is trying to distinguish between Klebsiella and Escherichia using a dichotomous key. Which test result would help differentiate these two genera?

Accepted Answer

Motility test: Klebsiella is nonmotile, Escherichia is motile.

Question 20

Which of the following best describes the role of the capsule in the pathogenesis of Klebsiella pneumoniae?

Accepted Answer

It protects the bacteria from phagocytosis.

Pathogenic Gram-Negative Cocci and Bacilli: Structure, Pathogenesis, and Clinical Importance

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