Question 1

Which of the following best describes the morphology of Escherichia coli (E. coli)?

Accepted Answer

Gram-negative bacilli, non-spore forming, motile, capsulated

Question 2

A 6-year-old boy presents with severe abdominal cramps, watery diarrhea progressing to bloody diarrhea, and vomiting after eating undercooked ground beef. Which E. coli pathotype is most likely responsible for his symptoms?

Accepted Answer

Enterohemorrhagic E. coli (EHEC)

Question 3

Which antigenic structure of E. coli is heat-stable and associated with the cell wall polysaccharide?

Accepted Answer

O (somatic) antigen

Question 4

Which laboratory medium is most appropriate for differentiating lactose fermenters from non-lactose fermenters among Enterobacteriaceae?

Accepted Answer

MacConkey's agar

Question 5

What is the primary cause of hemolytic uremic syndrome (HUS) in EHEC infections?

Accepted Answer

Inhibition of host protein synthesis by Shiga-like toxin

Question 6

Which of the following is a distinguishing biochemical feature of E. coli on MacConkey's agar?

Accepted Answer

Produces rose-pink colonies due to lactose fermentation

Question 7

Which of the following is NOT a disease caused by E. coli?

Accepted Answer

Tetanus

Question 8

A stool sample from a suspected EHEC O157:H7 infection is cultured on sorbitol MacConkey's agar. What result would you expect?

Accepted Answer

Colorless colonies due to non-sorbitol fermentation

Question 9

Which of the following Enterobacteriaceae is a non-lactose fermenter?

Accepted Answer

Salmonella species

Question 10

Which test result pattern is characteristic for E. coli in the IMViC series?

Accepted Answer

$$++--$$

Question 11

Which of the following is a key difference between Enterobacteriaceae and Pseudomonas aeruginosa?

Accepted Answer

Enterobacteriaceae are oxidase negative, while Pseudomonas aeruginosa is oxidase positive

Question 12

Which of the following best explains why E. coli is the most common cause of uncomplicated urinary tract infections (UTIs)?

Accepted Answer

It possesses fimbriae that facilitate adhesion to uroepithelial cells

Question 13

Which of the following is a heat-labile antigen found in E. coli?

Accepted Answer

H antigen

Question 14

A patient with hospital-acquired pneumonia is found to have Gram-negative bacilli in their sputum. Which of the following features would help confirm the organism as E. coli?

Accepted Answer

Motile, non-spore forming, Gram-negative bacilli

Question 15

Which of the following is the correct sequence for laboratory diagnosis of E. coli infection?

Accepted Answer

Sample collection → Gram stain → Culture on MacConkey's agar → Biochemical identification

Question 16

Which of the following is a common source of EHEC infection leading to outbreaks of hemolytic uremic syndrome?

Accepted Answer

Contaminated meat and dairy products

Gram-Negative Rods: Enterobacteriaceae and Escherichia coli

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