Question

1. The differential agent in MacConkey agar is ________.

• neutral red

• bile salts

• crystal violet

• lactose

2. The pH indicator neutral red used in MacConkey agar will cause a color change to ________ when acidic conditions from fermentation of lactose occur.

• yellow

• orange

• pink

• metallic green

3. Crystal violet and bile salts are used as ________ in MacConkey agar.

• detecting agents

• pH indicators

• selective agents

• differential agents

4. MacConkey agar is used primarily in ________ testing while EMB (Eosin Methylene Blue) agar is used for ________ testing.

• environmental; diagnostic

• selective; differential

• diagnostic; environmental

• differential; selective

5. MacConkey agar is selective against ________.

• gram-negative organisms

• gram-positive enterics

• gram-negative enterics

• gram-positive organisms

Answer 1

1)

Neutral red

It differentiate between lactose fermenter and lactose non-fermenters. Lactose fermenters give pink colonies and non-fermenters give yellow colonies.

2)

pink

When lactose is utilized, acids are Produced by lactose fermenters which lower the pH around the colony. Neutral red, in lower pH turns pink.

3)

selective agents

They both inhibit the growth of gram positive bacteria.

4)

environmental ; diagnostic

5)

Selective against gram positive organisms.