Question 1

Why is immersion oil used with the 100x objective lens in bright-field microscopy when observing bacteria?

Accepted Answer

It minimizes light refraction by matching the refractive index of glass, resulting in a clearer image at high magnification.

Question 2

Which of the following is NOT a true form of bacterial motility?

Accepted Answer

Brownian movement

Question 3

A student is preparing a negative stain to observe bacterial capsules. Why is negative staining preferred over heat-fixing and simple staining in this scenario?

Accepted Answer

Negative stains do not penetrate the capsule, allowing the capsule to appear as a clear halo around the cell.

Question 4

Which method is most effective for sterilizing nutrient agar before pouring plates?

Accepted Answer

Autoclaving at $$121^\circ C$$ for 15 minutes

Question 5

What is the main purpose of subculturing in microbiology?

Accepted Answer

To keep cells alive and maintain pure cultures

Question 6

When performing a streak plate, what is the main purpose of sterilizing your inoculating loop between each streak?

Accepted Answer

To dilute the bacterial sample and obtain isolated colonies

Question 7

On Mannitol Salt Agar (MSA), which result indicates that a bacterium can ferment mannitol?

Accepted Answer

Growth with a yellow medium

Question 8

Turbidity measurement is realized by a spectrophotometer that reads the:

Accepted Answer

Absorbance value, light scattering

Question 9

Why is heat-fixing important before staining bacterial smears?

Accepted Answer

It kills bacteria and permanently binds them to the slide

Question 10

Which reagent in the Gram stain procedure is responsible for forming large complexes with peptidoglycan, helping to retain the primary stain in Gram-positive bacteria?

Accepted Answer

Iodine solution

Question 11

A bacterial sample is stained using the acid-fast procedure. Which property of the cell wall is responsible for the acid-fast characteristic?

Accepted Answer

High content of mycolic acids

Question 12

In a carbohydrate fermentation test, a phenol red indicator turns yellow. What does this indicate?

Accepted Answer

The bacteria produced acid

Question 13

What is the main purpose of the enzyme $$\beta-$$galactosidase in bacteria?

Accepted Answer

To break down lactose

Question 14

Which of the following is NOT a product that forms once flavoproteins reduce $$O_2$$?

Accepted Answer

Sodium hydroxide

Question 15

A positive catalase test is indicated by the formation of bubbles when hydrogen peroxide is added to a bacterial colony. What do these bubbles contain?

Accepted Answer

Oxygen gas

Question 16

Which test is used to determine if a bacterium can break down the amino acid tryptophan?

Accepted Answer

Indole Test

Question 17

In the Methyl Red (MR) test, what does a red color after adding the indicator mean?

Accepted Answer

The bacteria produced a lot of acid from glucose fermentation

Question 18

In the gelatin hydrolysis test, which result indicates a positive test for gelatinase activity?

Accepted Answer

Medium becomes liquid

Question 19

Which of the following is NOT within phenylalanine agar?

Accepted Answer

None of the above

Question 20

During a nitrate reduction test, what must appear in the culture tube to prove positive for nitrate reduction?

Accepted Answer

A red color after adding nitrate reagents

Microbiology Laboratory Techniques and Concepts: Study Guide

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