As a part of the basic research for the improvement of the method for detection of Shigalike toxin producing Escherichia coli O157: H7 (hereinafter called “E. coli O157”) from raw meat, we examined the enrichment culture method for E. coli O157 injured by heating, by combination of culture medium (mEC-Nb, TSB), incubation time (5, 10, 20 hr), temperature (37°C, 42°C), and method (static, shaken). The examination also tested the efficacy of novobiocin for some species of bacteria which compete with E. coli O157.
The results of the examination are as follows.
1) It was shown that the enrichment from very few (10-3 cfu/ml) E. coli O157 injured by heating to 106 cfu / ml or more in an enrichment culture using mEC-Nb medium prepared by the official method took 20 hours, regardless of the incubation temperature or method.
2) After 10 hours or more of enrichment in TSB, the cfu count of E. coli O157 injured by heating was greater at 42°C than at 37°C, irrespective of the incubation method.
3) It was confirmed that the growth of bacteria which would compete with E. coli O157 in the enrichment was inhibited by the addition of 20 mg/l novobiocin to the culture medium.
