Description
Amyl Eosin Methylene Blue Agar (Levine), AM 55, is used to differentiate lactose fermenting from non-lactose fermenting enterobacteriaceae, and conforms to the Standards specified in APHA1,2,3 for examination of water and waste-water, dairy products and foods, as well as to the Australian Standards requirements4. It’s principle use is to confirm provisional tests for the presence of coliform organisms in water, milk and foods and to differentiate Escherichia coli from other coliforms.
Eosin Methylene Blue Agar was initially described by Holt-Harris and Teaque5. They utilised a combination of eosin and methylene blue which distinguished colonies of lactose fermenting organisms from the lactose non-fermenters. Levine modified this formulation by removing the sucrose and increasing the lactose and agar content6,7. The resulting medium clearly differentiated E. coli from E. aerogenes. Colonies of E. coli are usually well separated, dark and exhibit a distinctive dark green metallic sheen when viewed with reflected light. With some variants this sheen is not observed, and with others the colonies may be larger. Colonies of E. aerogenes are larger in size, pinkish lavender in colour with brownish centres, and have a tendency to coalesce. Sheen is usually not observed.
The success of this medium is dependent upon the quality of the dyes, their exact concentration and the preparation of the dehydrated product.
