Question

1.

Which genus contains acid-fast bacteria?

a. Bacillus

b. Staphylococcus

c. Streptococcus

d. Mycobacterium

2.

What component of the cell wall is responsible for the manner in which acid-fast bacteria absorb and

release stain?

a. isoniazid

b. mycolic acid

c. lipopolysaccharide

d. peptidoglycan

3.

In a properly done acid-fast stain, non-acid-fast bacteria will appear what color?

a. purple

b. pink

c. green

d. blue

4. Which disease is caused by members of the genus Mycobacterium?

a. cholera

b. diabetes

c. leprosy

d. tetanus

5. An acid-fast stain is an example of a

a. simple stain.

b. negative stain.

c. structural stain.

d. differential stain.

6. Define the following term using the laboratory exercise or glossary:

Differential stain:

7.List each of the reagents used in an acid-fast stain, along with its purpose in the staining process.

8.Why is an acid-fast stain used so much less frequently than a Gram stain?

Answer 1

1) Mycobacterium

Acid-fast bacteria are gram-positive, but in addition to peptidoglycan, the outer membrane or envelope of the acid-fast cell wall of contains large amounts of glycolipids, especially mycolic acids that in the genus Mycobacterium, make up approximately 60% of the acid-fast cell wall.

2) mycolic acid

The acid-fast stain is a differential stain used to identify acid-fast organisms such as members of the genus Mycobacterium .

Acid-fast organisms are characterized by wax-like, nearly impermeable cell walls; they contain mycolic acid and large amounts of fatty acids, waxes, and complex lipids. Acid-fast organisms are highly resistant to disinfectants and dry conditions.

Because the cell wall is so resistant to most compounds, acid-fast organisms require a special staining technique. The primary stain used in acid-fast staining, carbolfuchsin, is lipid-soluble and contains phenol, which helps the stain penetrate the cell wall. This is further assisted by the addition of heat. The smear is then rinsed with a very strong decolorizer, which strips the stain from all non-acid-fast cells but does not permeate the cell wall of acid-fast organisms. The decolorized non-acid-fast cells then take up the counterstain.

3) Blue

(Acid fast bacteria stained pink)

4) Leprosy