Abstract
ABSTRACT E. coli ATCC 11775 was heat injured at 59, 62, and 69°C, and recovered by a modification of the conventional coliform count on VRB. Four enrichment media, four selective overlay media, and four preincubation periods were tested to determine the optimal method for recovery of injured coliforms. Preincubation of injured E. coli for 2 hr on tryptone glucose extract (TGE) medium or plate count agar (PCA) significantly increased recovery of injured cells. Single strength violet red bile (VRB) agar gave higher recoveries than double strength VRB. No significant differences were observed between counts on boiled and sterilized VRB. We recommend the use of sterilized VRB since it is more convenient to prepare and store. Of the four enrichment and selective media examined, the recovery media of choice were TGE or PCA when used in combination with the sterilized VRB as the overlay medium. Therefore, preincubation for 2 hr with TGE or PCA overlayed with sterilized VRB is recommended for optimal recovery of injured E. coli.
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