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
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