Selective and Differential Media

• Selective media– Media designed to inhibit the growth of some

organisms while encouraging the growth of others

• Differential media– Media that contains substances (indicators) that

reveal differences between organisms

• Media can be both selective and differential.

Mannitol Salt agar

Both a selective and a differential medium

PEAPhenylethyl Alcohol Agar

A selective media that inhibits the growth of most Gram negative microbes

Blood agar

EMBEosin

Methylene Blue

Both a selective and a differential medium. Dyes inhibit Gram positives

HEA (Hektoen

Enteric Agar)

Both a selective and a differential medium. Bile salts inhibit Gram positives

HE Agar Plates

Hektoen enteric (HE) agar. Salmonella produces greenish colonies with black centers as

shown in the left panel. Enterobacter produces bright orange colonies as shown in the

right panel.

MacConkey’s Agar

Both a selective and a differential medium. Bile salts and crystal violet inhibit Gram positive bacteria