Lecture 3

Question 1

Which bacterial genus are very difficult to stain? Once stained, how do they retain the stain?

Answer 1

Mycobacterium. Once stained they are able to retain the stain very strongly. Even when treated with dilute HCl or H2SO4.

Question 2

What type of bacteria require acid fast stain? And why? Name one bacterial.

Answer 2

Bacteria with the presence of large amounts of lipids in their cell walls. Mycobacterium.

Question 3

Name two important acid-fast bacteria

Answer 3

Mycobacterium tuberculosis and Mycobacterium leprae

Question 4

What is the meaning of etiology and etiological?

Answer 4

Etiology is the meaning of the science of the cause of diseases and operation. Etiological is the an adjective relating to the cause of origins.

Question 5

Explain the 4 step acid-fast stain procedure

Answer 5

1. The heat-fixed smear is treated with covering it with a paper towel that has been saturated in Carbol fuschin. The slide is heated by a Bunsen burner for 5 min (until streamed). It’s important that it does not boil.
2. Remove the paper and rinse with water.
3. Drip diluted Hal or H2SO4 until the colour ceases to run. Rinse with water.
4. Stain with Methylene blue for 1-2 min. Rinse with water.

Question 6

Name the primary and secondary dyes in acid-fast staining.

Answer 6

Primary=carbol fuschin

Secondary= methylene blue

Question 7

Explain the phenomenon that occurs to acid-fast bacteria during this staining process.

Answer 7

Acid-fast bacteria retain the pink primary stain and other bacteria are decolourized by the acid-then stained blue.

Question 8

Define a culture a pure culture and a mixed culture.

Answer 8

A culture is any growth of a microorganism in a medium. A pure culture contains only one kind of microorganism. A mixed culture contains more that one kind of microorganism.

Question 9

Define isolation.

Answer 9

Isolation is the separation of a particular microorganism from the mixed population that can occur under natural circumstances.

Question 10

Define cultivation

Answer 10

The growth of the microorganism in a culture medium under lab conditions.

Question 11

Define a complex and synthetic medium

Answer 11

A complex medium is non synthetic and it contains ingredients of unknown chemical composition. A synthetic medium is one that has a known chemical composition.

Question 12

What forms of media are available?

Answer 12

Liquid, solid or gel

Question 13

Define inoculation

Answer 13

the addition of a microorganism to a culture medium.

Question 14

Name common gelling agents, and which is the most often used.

Answer 14

Agar, gelatin and silica gel. Agar is the most often used.

Question 15

Define agar slant, agar butt and agar plate.

Answer 15

1. Agar slant are prepared to let the agar media solidify while the tube is slanted. 2. Agar butt are prepare to let the agar media solidify in the tubes. 3. Agar plate is when the agar medium is poured in the lower half of a Petri plate which is covered and the medium is allowed to harden.

Question 16

Which are the Agar preparations present the most advantages?

Answer 16

The agar plate- larger surface area.

Question 17

What is the w/v of agar to a liquid broth for a satisfactory nutrient medium? Please give an example.

Answer 17

1.5%-2% w/v. 2.5 g of agar should be added to 500ml of nutrient liquid.

Question 18

When do we use a acid fast staining process?

Answer 18

When dealing with acid fast bacteria such as Mycobacterium tuberculosis and Mycobacterium leprae.

Question 19

What colour does the Acid-fast stain retain? And why?

Answer 19

Pink, the non acid bacteria are decolourized by the acid and then stained blue.