Q: Which of the following equations correctly represents the calculation for total magnification in a brightfield microscope?

$$\text{Total Magnification} = \text{Objective Lens} \times \text{Ocular Lens}$$

Question 1

Which of the following best describes the main purpose of Koch’s postulates in microbiology?

Accepted Answer

To establish a causal relationship between a specific microorganism and a specific disease.

Question 2

A microbiologist isolates a bacterium from a diseased animal, grows it in pure culture, and injects it into a healthy animal, which then develops the same disease. According to Koch’s postulates, what is the next step?

Accepted Answer

Re-isolate the same microorganism from the experimentally infected animal.

Question 3

Which ingredient in the nutrient agar recipe acts as the solidifying agent?

Accepted Answer

Agar

Question 4

A blood agar plate is best described as which type of medium?

Accepted Answer

Enriched and differential

Question 5

What is the main difference between blood agar and chocolate agar?

Accepted Answer

Blood agar contains intact red blood cells, while chocolate agar contains lysed red blood cells.

Question 6

Which of the following best explains why Eosin Methylene Blue (EMB) agar is both selective and differential?

Accepted Answer

It contains dyes that inhibit Gram-positive bacteria and lactose to differentiate fermenters.

Question 7

On EMB agar, which result would you expect from a strong lactose fermenter such as Escherichia coli?

Accepted Answer

Colonies with a metallic green sheen

Question 8

A microbiologist wants to count the number of viable bacteria in a sample. Which plating technique should they use for the most accurate results?

Accepted Answer

Spread plate

Question 9

Which of the following equations correctly represents the calculation for total magnification in a brightfield microscope?

Accepted Answer

$$	ext{Total Magnification} = 	ext{Objective Lens} 	imes 	ext{Ocular Lens}$$

Question 10

Which of the following best describes the growth pattern of obligate anaerobes in a thioglycollate broth tube?

Accepted Answer

Growth only at the bottom of the tube

Question 11

A sample is diluted 1:100 and 1 mL is plated, resulting in 37 colonies. What is the concentration of bacteria in CFU/mL? Use the formula $$C = \frac{n}{s 	imes d}.$$

Accepted Answer

$$C = 3700$$ CFU/mL

Question 12

Which of the following best explains why MacConkey agar is both selective and differential?

Accepted Answer

It contains bile salts and crystal violet to inhibit Gram-positive bacteria and lactose to differentiate fermenters.

Question 13

On XLD agar, which result would indicate the presence of Salmonella species?

Accepted Answer

Red colonies with black centers

Question 14

Which of the following best describes the main function of agar deep tubes in microbiology?

Accepted Answer

To grow bacteria that require less oxygen and to check for motility

Question 15

Which of the following best describes the difference between the spread plate and pour plate methods?

Accepted Answer

Spread plate spreads bacteria on the surface, while pour plate mixes bacteria with molten agar.

Question 16

Which of the following best explains why plates are incubated upside down after streak plating?

Accepted Answer

To prevent contamination from airborne particles and reduce condensation on the agar surface.

Question 17

Which of the following best describes the main use of CLED agar?

Accepted Answer

To isolate and differentiate urinary pathogens and prevent Proteus swarming.

Question 18

Which of the following best describes the result of a lactose fermenter on MacConkey agar?

Accepted Answer

Pink/red colonies

Question 19

Which of the following best describes the main selective agent in Mannitol Salt Agar (MSA)?

Accepted Answer

High salt concentration (7.5% NaCl)

Microbiology Laboratory Techniques and Media: Study Notes

Study Guide - Practice Questions

Study Guide - Flashcards