A new direct plate method for the enumeration ofEscherichia coliin frozen foods

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Abstract
A new method was devised, incorporating a resuscitant stage, which allows direct isolation of E. coli biotype I, Irregular type II and Irregular type VI. Rapid indole tests on the distinctive colonies produced enable determinations of E. coli biotype I to be made within 24 h. This method employs materials of low cost and achieves complete recovery of injured cells. It also detects not only anaerogenic strains but those which are slow in producing acid from lactose or give negative results by other methods. If required, further study of isolates can be made after the indole test. Comparisons were made between conventional methods, the new method and a similar direct plate method. The implications of the higher counts obtained by the 2 latter methods are discussed in relation to microbiological specifications and standards for frozen foods.

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