Question 1

Why can't Gram staining alone be used to distinguish between members of Enterobacteriaceae and Pseudomonas?

Accepted Answer

Both are Gram-negative bacilli and appear similar under Gram stain.

Question 2

Which of the following is a medically important member of Enterobacteriaceae commonly referred to as a 'coliform'?

Accepted Answer

Escherichia coli

Question 3

Which of the following is NOT a general characteristic of Enterobacteriaceae?

Accepted Answer

They are Gram-positive cocci.

Question 4

Which genera of Enterobacteriaceae are considered normal microbiota but can act as opportunistic pathogens?

Accepted Answer

Klebsiella and Enterobacter

Question 5

Glucose Non-Fermenting Gram-Negative Bacilli differ from Enterobacteriaceae in which of the following ways?

Accepted Answer

They do not ferment glucose, while Enterobacteriaceae do.

Question 6

To which family does Pseudomonas belong?

Accepted Answer

Pseudomonadaceae

Question 7

A patient with cystic fibrosis develops a chronic lung infection. Which organism is most likely responsible, and what is its clinical significance?

Accepted Answer

Pseudomonas aeruginosa; it causes opportunistic infections and is resistant to many antibiotics.

Question 8

What does the oxidase test detect?

Accepted Answer

The presence of cytochrome c oxidase enzyme.

Question 9

What is the color of a positive oxidase test reaction, and what is the end product formed?

Accepted Answer

Purple color; indophenol is formed.

Question 10

How does the oxidase test help distinguish between Enterobacteriaceae and Pseudomonas?

Accepted Answer

Pseudomonas is oxidase positive, Enterobacteriaceae is oxidase negative.

Question 11

Cetrimide agar is used to select for which organism, and what is its special component?

Accepted Answer

Pseudomonas aeruginosa; cetrimide inhibits other bacteria.

Question 12

Which two pigments are produced by Pseudomonas aeruginosa, and are they water soluble?

Accepted Answer

Pyocyanin (blue-green, water soluble) and pyoverdine (yellow-green, water soluble)

Question 13

What are the typical characteristics of Pseudomonas aeruginosa colonies on cetrimide agar?

Accepted Answer

Blue-green color and grape-like odor

Question 14

MacConkey agar is best described as:

Accepted Answer

Both selective and differential; bile salts and crystal violet make it selective, lactose and neutral red make it differential.

Question 15

Which organisms typically grow on MacConkey agar?

Accepted Answer

Gram-negative bacteria

Question 16

On MacConkey agar, what does a pink colony indicate?

Accepted Answer

The organism ferments lactose, producing acid that turns the pH indicator pink.

Question 17

Which of the following best describes the growth of Enterobacteriaceae and Pseudomonas on MacConkey agar?

Accepted Answer

Enterobacteriaceae: pink colonies if lactose fermenter; Pseudomonas: colorless colonies (non-lactose fermenter)

Question 18

Can all members of Enterobacteriaceae ferment lactose?

Accepted Answer

No, only some members can ferment lactose.

Question 19

The Enteropluri test allows for how many different biochemical tests to be performed in a single tube, and what is its main advantage?

Accepted Answer

12 tests; rapid identification of Enterobacteriaceae

Question 20

A clinical lab receives a Gram-negative rod that is oxidase positive, grows on cetrimide agar with blue-green pigment, and produces a grape-like odor. Which organism is most likely present?

Accepted Answer

Pseudomonas aeruginosa

Microbiology Study Guide: Enterobacteriaceae, Pseudomonas, and Diagnostic Media

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