Question 1

Which of the following characteristics is shared by all members of the Enterobacteriaceae family?

Accepted Answer

They are gram-negative bacilli

Question 2

A patient sample is streaked on MacConkey agar. After incubation, the colonies appear pink. What does this indicate about the organism?

Accepted Answer

It is a lactose fermenter and likely a member of Enterobacteriaceae

Question 3

Which of the following best explains why a Gram stain alone is insufficient to distinguish between Enterobacteriaceae and Pseudomonas species?

Accepted Answer

Both are gram-negative bacilli and require biochemical tests for further differentiation

Question 4

Refer to the third image. What does the color change on the swab indicate in the oxidase test?

Accepted Answer

The organism is oxidase-positive and possesses cytochrome oxidase

Question 5

Which pigment is specifically produced by Pseudomonas aeruginosa on cetrimide agar and is water-soluble?

Accepted Answer

Pyocyanin

Question 6

A clinical isolate grows on cetrimide agar, producing a blue-green pigment and a grape-like odor. What is the most likely identity of this organism?

Accepted Answer

Pseudomonas aeruginosa

Question 7

Which of the following is the correct sequence of steps for performing the oxidase test?

Accepted Answer

Remove oxidase swab, collect bacterial growth, observe for color change within 10 seconds

Question 8

Which of the following statements about MacConkey agar is TRUE?

Accepted Answer

It is both selective and differential, using bile salts and crystal violet to inhibit gram-positives and neutral red to indicate lactose fermentation

Question 9

Refer to the seventh image. Which plate shows a strong lactose fermenter and what is the expected pH change?

Accepted Answer

The left plate; pH decreases below 6.8

Question 10

Which of the following genera is NOT considered a strict pathogen associated with gastroenteritis?

Accepted Answer

Proteus

Question 11

What is the main function of cytochrome oxidase in the electron transport chain, as shown in the first image?

Accepted Answer

To transfer electrons from cytochrome c to oxygen, forming water

Question 12

Which of the following is a distinguishing feature of Pseudomonas aeruginosa compared to Enterobacteriaceae?

Accepted Answer

It produces a blue-green pigment on cetrimide agar

Question 13

A laboratory technician uses the streak plate technique (see sixth image) to isolate bacteria. What is the primary purpose of this technique?

Accepted Answer

To obtain isolated colonies from a mixed culture

Question 14

Which of the following statements about the EnteroPluri-Test is correct?

Accepted Answer

It allows for 15 different biochemical tests to be performed in a single tube

Question 15

Which of the following is a common misconception about the oxidase test?

Accepted Answer

A positive result means the organism is a member of Enterobacteriaceae

Question 16

Which of the following best describes the clinical significance of Pseudomonas aeruginosa?

Accepted Answer

It is a common cause of nosocomial infections, especially in immunocompromised patients

Question 17

Which of the following is NOT a characteristic of Enterobacteriaceae?

Accepted Answer

They are oxidase-positive

Question 18

Which of the following statements about glucose non-fermenting gram-negative bacilli is TRUE?

Accepted Answer

They are commonly found in soil and water and may cause infections in immunosuppressed individuals

Question 19

Which of the following is the correct interpretation of a MacConkey agar plate with colorless colonies?

Accepted Answer

The organism is a non-lactose fermenter

Question 20

Which of the following is the correct formula for the calculation of the EnteroPluri-Test code for a set of three test results (positive, negative, positive) in a compartment with values 4, 2, and 1?

Accepted Answer

$$4+0+1=5$$

Isolation and Identification of Enterobacteriaceae and Pseudomonas: Microbiology Lab Study Guide

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