Comparison of Agar Media for Detection and Quantification of Shiga Toxin–Producing Escherichia coli in Cattle Feces

ABSTRACT The isolation and quantification of non-O157 Shiga toxin–producing Escherichia coli (STEC) from cattle feces are challenging. The primary objective of this study was to evaluate the performance of selected agar media in an attempt to identify an optimal medium for the detection and quantification of non-O157 STEC in cattle feces. Comparison studies were performed using CHROMagar STEC, Posse differential agar (Posse), Posse modified by the reduction or addition of antimicrobials, STEC heart infusion washed blood agar with mitomycin C (SHIBAM), and SHIBAM modified by the addition of antimicrobials. Fourteen STEC strains, two each belonging to serogroups O26, O45, O103, O111, O121, O145, and O157, were used to test detection in inoculated fecal suspensions at concentrations of 102 or 103 CFU/g. One STEC strain from each of these seven serogroups was used to estimate the concentration of recovered STEC in feces inoculated at 103, 104, or 105 CFU/g. Significantly more suspensions (P < 0.05) were posit...