Question 1

Which of the following best describes the main advantage of using agar instead of gelatin as a solidifying agent in bacterial culture media?

Accepted Answer

Agar is digested by fewer bacteria and remains solid at higher incubation temperatures.

Question 2

A laboratory technician is preparing a nutrient agar plate. Which of the following steps is essential to minimize contamination during the pouring process?

Accepted Answer

Keep the flask at an angle and pour near a flame to reduce airborne contaminants.

Question 3

Which of the following is NOT a component of aseptic technique in the laboratory?

Accepted Answer

Allowing culture media to remain open to air for extended periods.

Question 4

A patient’s blood sample is suspected to contain Mycobacterium tuberculosis. Which culture medium would be most appropriate for isolating this organism?

Accepted Answer

Lowenstein–Jensen medium

Question 5

Which of the following best explains why specimens for bacterial culture should be transported to the laboratory as soon as possible or stored at $$4^\circ C if $$delayed?

Accepted Answer

To preserve the viability of delicate bacteria and minimize overgrowth of contaminants.

Question 6

Which of the following statements about Gram staining is correct?

Accepted Answer

Gram-positive bacteria appear purple and Gram-negative bacteria appear pink/red.

Question 7

A microbiologist wants to isolate and study only Neisseria gonorrhoeae from a mixed clinical sample. Which medium should be used?

Accepted Answer

Thayer Martin medium

Question 8

Which of the following is a key reason for using a flame to sterilize the mouth of a culture tube before and after transferring bacteria?

Accepted Answer

To kill any contaminants present at the tube opening.

Question 9

Which of the following best describes a 'complex medium' in microbiology?

Accepted Answer

A medium containing ingredients such as peptones or meat extracts with unknown exact composition.

Question 10

A student observes a petri dish with colonies that have a metallic green sheen on eosin methylene blue (EMB) agar. What is the most likely organism present?

Accepted Answer

Escherichia coli

Question 11

Which of the following is the correct format for writing the scientific name of the bacterium that causes anthrax?

Accepted Answer

$$Bacillus anthracis$$

Question 12

Which of Koch’s postulates is directly tested when a pure culture of a suspected pathogen is introduced into a healthy animal?

Accepted Answer

The cultured microorganism should cause disease when introduced into a healthy organism.

Question 13

A microbiologist is using an inoculating loop to transfer bacteria. Why is it important to let the loop cool after flaming before touching the sample?

Accepted Answer

To avoid killing the bacteria with excessive heat.

Question 14

Which of the following best describes the purpose of using selective media in microbiology?

Accepted Answer

To encourage the growth of specific microorganisms while inhibiting others.

Question 15

A urine specimen for bacterial culture is delayed in transport to the lab. What is the most likely consequence if it is not refrigerated at $$4^\circ C$$?

Accepted Answer

The bacterial count may increase, leading to a falsely high result.

Question 16

Which of the following is a distinguishing feature of blood agar compared to chocolate agar?

Accepted Answer

Blood agar allows observation of hemolysis patterns, while chocolate agar does not.

Question 17

Which of the following equations correctly represents the preparation of nutrient agar from nutrient broth?

Accepted Answer

$$	ext{Nutrient Broth} + 	ext{Agar} = 	ext{Nutrient Agar}$$

Question 18

Which of the following best describes a colony forming unit (CFU)?

Accepted Answer

A group of genetically identical bacteria that arise from a single progenitor cell.

Question 19

Which of the following is a correct statement about the use of autoclaving in media preparation?

Accepted Answer

Autoclaving sterilizes the media by using high pressure and temperature.

Question 20

A microbiologist observes a test tube with a semi-solid medium and notices bacterial growth radiating from the stab line. What property is being tested?

Accepted Answer

Bacterial motility

Microbes in the Environment & Handling Bacteria: Study Notes for Microbiology

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