Question 1

Which component of the Mycobacterium cell wall is primarily responsible for its acid-fast property, as shown in the first image?

Accepted Answer

Mycolic acid

Question 2

A patient presents with cloudy patches in the lungs on a chest X-ray (see image 2). Which staining technique would be most appropriate to confirm a diagnosis of tuberculosis?

Accepted Answer

Acid-fast stain

Question 3

In the acid-fast staining procedure, what color will acid-fast bacteria appear under the microscope, as shown in image 3?

Accepted Answer

Pink/red

Question 4

Which of the following best explains why non–acid-fast bacteria appear blue after acid-fast staining (see image 4)?

Accepted Answer

They are decolorized by acid-alcohol and take up the counterstain.

Question 5

Which phase of the bacterial growth curve (see images 5 and 6) is characterized by a balance between cell division and cell death?

Accepted Answer

Stationary phase

Question 6

If an antibiotic delays the start of bacterial growth, which phase of the bacterial growth curve is extended?

Accepted Answer

Lag phase

Question 7

Given the equation $$N(t) = N_0$ 	imes e$$^{kt}$$, what does the variable k$ represent?

Accepted Answer

Growth rate constant

Question 8

A culture starts with $$500$$ cells and doubles every hour. How many cells will there be after $$4$$ hours? Use $$N(t) = N_0$ 	imes 2^t.$$

Accepted Answer

$$8,000$$

Question 9

Which of the following errors would most likely result in a false negative acid-fast stain?

Accepted Answer

Using a culture that is too old

Question 10

What is the main advantage of the Kinyoun method over the Ziehl-Neelsen method for acid-fast staining?

Accepted Answer

It does not require heat, reducing safety risks.

Question 11

Which of the following best describes the role of phenol in the Kinyoun acid-fast staining method?

Accepted Answer

It serves as a mordant to enhance dye penetration.

Question 12

If the exponential phase of a bacterial growth curve is less steep after antibiotic treatment, what does this indicate?

Accepted Answer

The antibiotic is effective in reducing the growth rate.

Question 13

Which equation would you use to calculate the number of generations per hour during exponential growth, as shown in image 7?

Accepted Answer

$$k = n/t$$

Question 14

Which of the following is a limitation of the acid-fast stain compared to the Gram stain?

Accepted Answer

It cannot differentiate between Gram-positive and Gram-negative bacteria.

Question 15

A student leaves the acid-alcohol decolorizer on a smear for too long during acid-fast staining. What is the most likely result?

Accepted Answer

All bacteria will appear blue.

Question 16

Which family does Mycobacterium tuberculosis belong to, as indicated in the study materials?

Accepted Answer

Mycobacteriaceae

Question 17

Which phase of the bacterial growth curve is most affected by nutrient depletion and waste accumulation?

Accepted Answer

Stationary phase

Question 18

If you start with $$2 	imes 10^3$ E. coli cells and the growth rate constant k = 0.7$ per hour, how many cells will there be after 5$ hours? Use N(t$$) = $$N_0$$ 	imes $$e^{kt}.$$

Accepted Answer

$$66,200$$

Question 19

Which of the following is NOT a possible source of error in the acid-fast staining procedure?

Accepted Answer

The culture was too young.

Question 20

Which of the following best describes why Mycobacterium species are resistant to drying and harsh environments?

Accepted Answer

Their cell walls contain high levels of mycolic acid.

Acid-Fast Staining and Bacterial Growth: Microbiology Study Guide

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