Primary Purpose
Grow Gram negative bacteria and differentiate between organisms which can ferment lactose and which cannot ferment lactose.
Type of medium
Selective (for Gram negative bacteria)
Differential (Lactose fermenting ability)
Nutrients for growth
Peptone
What inhibits the Gram negative organisms?
Bile salts
Crystal violet (added sometimes)
How are lactose fermentors recognized?
The organisms which breakdown lactose produce acid. The acid production is identified by pink color because of the presence of the indicator Neutral red in the medium.
Osmotic balance is maintained by NaCl
If swarming of Proteus is to be inhibited, NaCl is not added.
pH of medium
7.1 +/- 0.2
Some facts about MacConkeys agar
-It is named after the scientist 'Alfred Theodore MacConkey' who developed it.
-It is a very common media to isolate E. coli
-Gram negative bile tolerant strains may grow on this agar.
-If you remove 'acC' from MacConkeys it will become Monkeys agar.
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