Isolation of Escherichia coli O157 from raw meat products.

This study has evaluated an enrichment and four subculture procedures for detection of Escherichia coli O157 in raw meat products. The combination of enrichment in modified tryptone broth incubated at 42 degrees C for 6 h, followed by immunomagnetic separation and subculture on to cefixime, tellurite sorbitol MacConkey agar was the most sensitive and selective procedure. Traditional subculture using 10 microliters and 100 microliters inocula and culture of centrifuged deposits were less satisfactory. A most probable number method was used to enumerate E. coli O157 in naturally contaminated samples associated with human cases. The results indicated that the samples contained < 0.3 to 2300 cfu g-1 of E. coli O157 which confirms that the infective dose for this organism is low.