Abstract
At low levels, enterohemorrhagic Escherichia coli should be selectively isolated by suppressing competing microflora in meat samples. In conventional methods, MacConkey II Agar with C-T Sorbitol (cefixime-tellurite, CT-SMAC) which utilizes the ability of E. coli O157 to ferment sorbitol, and media containing E.coli-specific chromogenic substrates, are used for detecting E. coli O157.
In this study, we compared two types of BD CHROMagarTM O157 for the isolation of enterohemorrhagic E. coli O157 (improved BD CHROMagarTM O157 and conventional BD CHROMagarTM O157) with CT-SMAC by using the Miles-Misra method and evaluating the recovers from ground beef and human fecal samples. The results obtained are described below:
1. In the inoculation test with three media by the Miles-Misra method, improved BD CHROMagarTM O157 inhibited the growth of all organisms except E. coli O157 better than the two other media and allowed easy differentiation from E. hermannii, which could not be distinguished on CT-SMAC.
2. In the E. coli O157 detection test for ground beef artificially inoculated with E. coliO157 at 1 cfu/g, the detection rate of improved BD CHROMagar TM O157 was 95%, CTSMAC 75% and conventional BD CHROMagarTM O157 40%, respectively.
4. In the E. coli O157 detection test for E. coli O157 positive human fecal samples, the detection rate of improved BD CHROMagarTM O157 was 54.5%, CT-SMAC 50% and conventional BD CHROMagarTM O157 22.7%, respectively.
