Question 1

Which of the following best explains the difference in pigment production observed in the two test tubes shown in the image, when both were inoculated with *Serratia marcescens* and incubated at different temperatures?

Accepted Answer

Pigment production in *Serratia marcescens* is optimal at room temperature, resulting in the red coloration, while higher temperatures (40°C) suppress pigment formation.

Question 2

When transferring *Serratia marcescens* from a slant to a deep using an inoculating needle, which of the following steps is essential to maintain aseptic technique?

Accepted Answer

Flaming the necks of both tubes before and after transfer.

Question 3

Which of the following characteristics distinguishes *Serratia marcescens* from many other Gram-negative rods?

Accepted Answer

It produces a distinctive red pigment at room temperature.

Question 4

A student accidentally forgets to flame the neck of the culture tube before and after transferring *Serratia marcescens*. What is the most likely consequence?

Accepted Answer

There is an increased risk of contaminating the culture.

Question 5

Why is it important to incubate one set of inoculated media at room temperature and another at 40°C when working with *Serratia marcescens*?

Accepted Answer

To determine the effect of temperature on pigment production and bacterial growth.

Question 6

Which of the following best describes the correct use of an inoculating loop when transferring bacteria from a slant to a broth?

Accepted Answer

The loop should be tapped gently against the side of the broth tube to dislodge the bacteria.

Question 7

Which of the following is a facultative anaerobe that can use both respiratory and fermentative metabolism?

Accepted Answer

*Serratia marcescens*

Question 8

A student observes no red pigment in a *Serratia marcescens* culture incubated at 40°C. What is the most likely explanation?

Accepted Answer

Pigment production is inhibited at higher temperatures.

Question 9

Which of the following steps is NOT part of the standard aseptic transfer technique?

Accepted Answer

Leaving the tubes open during the entire procedure.

Question 10

If a student uses an inoculating loop instead of a needle to stab a deep, what is the most likely outcome?

Accepted Answer

The stab will be too wide, potentially disrupting the medium.

Question 11

Which of the following best describes the morphology and motility of *Serratia marcescens*?

Accepted Answer

Rods, motile with peritrichous flagella

Question 12

Why is it important to label test tubes with masking tape before inoculation?

Accepted Answer

To ensure accurate identification of cultures after incubation.

Question 13

Which of the following is the correct sequence for aseptic transfer of bacteria from a slant to a broth?

Accepted Answer

Flame loop → uncap tubes → flame necks → transfer bacteria → recap tubes → flame loop

Question 14

A student observes growth only along the stab line in a deep inoculated with *Serratia marcescens*. What does this indicate about the organism's motility?

Accepted Answer

The organism is non-motile.

Question 15

Which of the following best describes the environmental distribution of *Serratia marcescens*?

Accepted Answer

It is found in soil, water, plant surfaces, and the digestive tracts of rodents and insects.

Microbial Culture Transfer Techniques and Serratia marcescens

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