Growth Media Type Mac Conkey Agar

Other common names

This product is widely known under the name Mac Conkey Agar, although it can be referred to as MAC agar.

Primary Use

MacConkey agar is used for the isolation non-fastidious Gram-negative or coliforms, in addition to differentiating their lactose fermentation abilities.

Technical characteristics

The typical medium composition:

Neutral red is red in colour at pH below 6.8

Fresh pH 7.4 ±0.2

Applications

A differential medium for the isolation of coliforms and intestinal pathogens in water, dairy products and biological specimens. The inclusion of bile salts prevents the growth of Gram positive bacteria. Fermentation of lactose in the media will result a change in pH which is detected by neutral red. 

Absorption of neutral red throughout growth will result in formation of red or pink colonies as a result of acid production by lactose fermenters. Strong lactose fermenting bacteria can cause bile salt precipitation which results in a pink halo in the medium surrounding the individual colonies or areas of confluent growth. Non-lactose fermenting bacteria will appear as off-white opaque colonies. 

In water testing, the medium can be used direct count of coli-aerogenes bacteria and it has the added advantage of inhibiting swarming of Proteus.

Related reading:

• Monitoring the clean room
• Environmental monitoring: how to maintain a cleanroom
• Keep it clean: considerations for pharmaceutical cleanrooms

Appearance

The prepared media is slightly opalescent, pinkish-red.