Question 1

Which of the following statements best describes what can be determined by direct observation of bacteria using microscopy and staining?

Accepted Answer

The cell shape, size, arrangement, motility, and presence/absence of certain structures

Question 2

A student is culturing bacteria on a selective and differential medium. What information can they obtain from this culture-based method?

Accepted Answer

The colony shape, size, arrangement, motility, biochemistry, and some aspects of metabolism

Question 3

Which of the following is NOT a step in proper aseptic technique when transferring a liquid culture?

Accepted Answer

Touching the loop to the bench to cool it before use

Question 4

Why is it important to adjust the collar of a Bunsen burner until a blue outer flame with an inner bright blue flame is achieved?

Accepted Answer

It ensures the flame is hot enough to sterilize equipment effectively

Question 5

Which biosafety cabinet class is required as a minimum for experiment protection and is most commonly used in microbiology labs?

Accepted Answer

Class II

Question 6

What is the primary method for sterilizing equipment in a microbiology laboratory?

Accepted Answer

Autoclaving

Question 7

A solution contains heat-sensitive solutes and cannot be autoclaved. Which sterilization method is most appropriate?

Accepted Answer

Filter sterilization using a 0.22 $\mu$m or 0.45 $\mu$m pore size filter

Question 8

Which of the following is a limitation of microscopic cell count for quantifying microbial numbers?

Accepted Answer

It cannot distinguish live from dead cells without a specific stain

Question 9

Given a plate count result of 120 colonies from plating 0.1 mL of a 10$^{-4}$ dilution, what is the CFU/mL in the original sample? Use the formula $	ext{CFU/mL} = \frac{	ext{CFU} 	imes 	ext{Dilution Factor}}{	ext{Volume plated in mL}}$.

Accepted Answer

$1.2 	imes 10^8$

Question 10

Why is drop plating often preferred over spread or pour plating for quantifying bacteria?

Accepted Answer

It enables multiple serial dilutions to be plated on a single plate, increasing throughput and efficiency

Question 11

A spectrophotometer is used to measure the optical density (OD) of a bacterial culture at 595 nm. What must be done to accurately estimate CFU/mL from OD readings?

Accepted Answer

Use a standard curve of OD vs. plate count CFU/mL

Question 12

Which of the following is a potential source of error in viable cell count (plate count) methods?

Accepted Answer

Inaccurate pipetting and improperly mixed samples

Question 13

What is the main advantage of using membrane filtration for water testing in microbiology?

Accepted Answer

It enables the concentration and enumeration of bacteria from large volumes of water

Question 14

Which of the following best describes the purpose of the Most Probable Number (MPN) method?

Accepted Answer

To estimate the concentration of bacteria in a sample using statistical analysis of growth in multiple tubes

Question 15

A laboratory is working with a pathogen classified as Risk Group 3. What is the minimum containment level (CL) required for this work?

Accepted Answer

Containment Level 3

Question 16

Which of the following is a correct definition of 'pure culture'?

Accepted Answer

A culture of bacteria on an agar plate derived from the same mother cell, if pure

Question 17

During a minimum inhibitory concentration (MIC) assay, what does a lower MIC value indicate?

Accepted Answer

The antibiotic is more effective against the test organism

Question 18

Which of the following is a key industrial use of bacteria?

Accepted Answer

Production of antibiotics and fermented foods

Question 19

Which of the following statements about the streak plate method is correct?

Accepted Answer

It is used to isolate pure cultures by forming discrete colonies from a mixed sample

Question 20

A researcher needs to confirm the presence of a specific DNA sequence in a bacterial sample. Which technique should they use?

Accepted Answer

Polymerase Chain Reaction (PCR)

Techniques in Microbiology: Culturing, Quantification, and Safety

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