A volume of 0.1 mL of appropriate dilutions was spread evenly on a dried surface of Tellurite-cefixime-sorbitol MacConkey (TC-SMAC, Oxoid, UK) agar plates . All inoculated plates were incubated at 37±0.5°C for 18-24 h. Typical colonies of E. coli O157 were colorless or neutral/gray with a smoky center and 1-2 mm in diameter. Five typical colonies were picked and cultured on nutrient agar slants and incubated at 35±0.5°C for 18-24 h for further identification by Levine’s eosin-methylene blue (L-EMB, Oxoid, UK) Agar which shows a characteristic green metallic shine colony of EHEC O157:H7.