Q: You are asked to enumerate bacteria using a serial dilution and plate count. If you plate $$0.1\ \mathrm{mL} of a$$ $$10^{-4}$$ dilution and count 50 colonies, what is the original concentration of bacteria in $$\mathrm{CFU/mL}$$?

$$5 \times 10$$^{5}$$\ \mathrm{CFU/mL}$$

Question 1

Which of the following is the correct procedure for discarding used gloves in a microbiology lab?

Accepted Answer

Dispose of them in the biohazard waste container.

Question 2

What is the first action you should take in the event of any emergency in the lab?

Accepted Answer

Notify your instructor and follow lab emergency protocols.

Question 3

Which piece of personal protective equipment (PPE) is essential when working with biohazardous materials?

Accepted Answer

Lab coat, gloves, and safety goggles.

Question 4

When carrying a microscope, which parts should you hold to ensure safe transport?

Accepted Answer

Hold the arm and support the base.

Question 5

Which of the following best describes the difference between prokaryotic and eukaryotic cells?

Accepted Answer

Eukaryotes have a nucleus; prokaryotes lack a nucleus.

Question 6

What is the main purpose of performing a wet mount preparation in microscopy?

Accepted Answer

To observe living organisms and their motility.

Question 7

Which step is critical for maintaining aseptic technique when transferring bacteria?

Accepted Answer

Sterilizing the inoculating loop before and after use.

Question 8

A student observes that after Gram staining, all bacteria appear red. Which of the following is the most likely cause?

Accepted Answer

The crystal violet stain was not applied.

Question 9

Where should you label a Petri plate before inoculation?

Accepted Answer

On the bottom (agar side).

Question 10

What is the correct way to store a Petri plate after inoculation?

Accepted Answer

Agar side up (lid down).

Question 11

Which streaking technique is commonly used to isolate pure bacterial colonies?

Accepted Answer

T-streak technique.

Question 12

You are asked to enumerate bacteria using a serial dilution and plate count. If you plate $$0.1\ \mathrm{mL} of a$$ $$10^{-4}$$ dilution and count 50 colonies, what is the original concentration of bacteria in $$\mathrm{CFU/mL}$$?

Accepted Answer

$$5 	imes 10$$^{5}$$\ \mathrm{CFU/mL}$$

Question 13

Which of the following best describes selective media?

Accepted Answer

Media that inhibits the growth of certain microbes while allowing others to grow.

Question 14

What makes MacConkey agar both selective and differential?

Accepted Answer

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

Question 15

In a fluid thioglycollate medium, what is the purpose of the indicator dye?

Accepted Answer

To visualize the oxygen gradient within the medium.

Question 16

Which oxygen requirement classification describes bacteria that grow only at the bottom of a thioglycollate tube?

Accepted Answer

Obligate anaerobes.

Question 17

A sugar fermentation tube contains a Durham tube and phenol red. If the medium turns yellow and a bubble forms in the Durham tube, what does this indicate?

Accepted Answer

Acid production and gas production from fermentation.

Question 18

Which medium is used to test for the presence of tryptophanase, and what color change indicates a positive result?

Accepted Answer

SIM medium; red color after adding Kovac's reagent.

Question 19

On a blood agar plate, which type of hemolysis is indicated by a clear, colorless zone around bacterial colonies?

Accepted Answer

Beta hemolysis.

Question 20

A patient’s sample is tested for plasma clotting using the coagulase test. What does a positive result indicate?

Accepted Answer

The presence of Staphylococcus aureus.

BIO221 Lab Material Review: Microbiology Laboratory Fundamentals

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