A novel chromogenic screening medium for isolation of enterohemorrhagic Escherichia coli

EHEC-chrom, a novel chromogenic screening agar medium for enterohemorrhagic Escherichia coli (EHEC) , was developed. A total of 52 EHEC strains, which were studied for the inclusivity study, grew and formed blue-green colored colonies on EHEC-chrom. When 43 gram-negative bacteria other than EHEC were inoculated for the exclusivity study, 10 strains grew and formed colorless colonies. A total of 28 gram-positive bacteria failed to grow and 1 yeast strain grew as colorless colonies. EHEC-chrom was compared with CHROMagar™ STEC, XM-EHEC agar and CT-MacConkey base agar with a specific sugar (CT-SorbitolMAC, CT-rhamnoseMAC and CT-sorboseMAC) as commercially available selective agar using 100 food samples artificially contaminated with low levels (<10 logCFU/25g) of EHEC. Numbers of samples from which EHEC was recovered by using EHEC-chrom, CHROMagar™ STEC, XM-EHEC agar and CT-MacConkey base agar with specific sugar were 62, 58, 59 and 60, respectively. Our results suggested EHEC-chrom was a useful alternative for EHEC screening in food.