EMB Agar (Eosin Methylene-blue Lactose Sucrose Agar)

EMB Agar

EMD Cat. No. 1.01347.0500

500 g

Selective agar proposed by HOLT-HARRIS and TEAGUE (1916) for the detection and isolation of pathogenic Enterobacteriaceae.

Mode of Action	Preparation
Experimental Procedure and Evaluation	Quality Control
Typical Composition (g/liter)	Literature
Picture/Image

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

Quality control

Test strains	Growth	Colony color	Metallic sheen
Escherichia coli ATCC 25922	good / very good	violet	+
Escherichia coli ATC 11775	good / very good	violet	+
Escherichia coli 194	good / very good	violet	+
Escherichia coli ATCC 23716	good / very good	violet	+
Escherichia coli ATCC 8739	good / very good	violet	+
Enterobacter cloacae ATCC 13047	fair / very good	pink, dark centre	+ / -
Salmonella typhimurium ATCC 14028	good / very good	colorless, transparent	-
Shigella flexneri ATCC 12022	good / very good	colorless, transparent	-
Bacillus cereus ATCC 11778	none / poor		-

Literature

HOLT-HARRIS, J.E., a. TEAGUE, O.A.: A new culture medium for the isolation of Bacillus typhosus from stools. - J. Infect. Dis., 18; 596-600 (1916).