lab 4-5

Question 1

MacConkey agar is what type of medium?

Answer 1

Selective : for gram negative. Inhibits growth of gram positive.

Differential: Medium indicates lactose fermenters vs non fermenters

Question 2

MacConkey agar contains?

Answer 2

Lactose
Bile salts
Crystal violet
Neutral red; ph indicator for lactose

Question 3

MacConkey agar w/o crystal violet would allow what?

Answer 3

grow of gram positive (Enterococcus and some Staphylococcus) - would ferment lactose and appear pink.

Question 4

What inhibits the growth of gram positive in the MacConkey agar?

Answer 4

Crystal violet + bile salts inhibit growth of gram +

Question 5

What color are lactose fermenters?

Answer 5

pink/red color and have a ph less than 6.8

Question 6

What color are non lactose fermenters?

Answer 6

Colorless. Or retain color of the medium.

Question 7

Application of MacConkey agar?

Answer 7

To isolate and differentiate members of Enterobacteriaceae based on ability to ferment lactose