EMB media

Mode of Action

The lactose and sucrose contained in this medium allow lactose- and sucrose-negative salmonellae and shigellae to be distinguished from lactose-positive coliform organisms and lactose-negative, sucrose-positive, accompanying flora (e.g. Proteus vulgaris, Citrobacter, Aeromonas hydrophila). The growth of undesired accompanying microorganisms, particularly Gram-positive bacteria, is largely inhibited by the dyes present in the medium

Typical Composition (g/liter)

Peptones 10.0; di-potassium hydrogen phosphate 2.0; lactose 5.0; sucrose 5.0; eosin Y, yellowish 0.4; methylene blue 0.07; agar-agar 13.5.

Preparation

Suspend 36 g in 1 liter of purified water. Autoclave (15 min at 121°C), pour plates.pH: 7.1 ± 0.2 at 25°C. The plates are clear and reddish-brown to violet-brown.

Experimental Procedure and Evaluation

Inoculate by spreading the sample material thinly on the surface of the plates.Incubation: 24 hours at 35°C aerobically.

Appearance of Colonies --> Microorganisms
Translucent, amber colored --> Salmonella, Shigella
Greenish, metallic sheen in reflected light, blue-black centre in transmitted light --> Escherichia coli
Colonies are larger than those of E. coli, mucoid, confluent, gray-brown centre in transmitted light --> Enterobacter, Klebsiella and others

Typical E.coli colonies