USE OF TELLURITE FOR THE SELECTION OF VEROCYTOTOXIGENIC ESCHERICHIA-COLI O157

Potassium tellurite was assessed for the selection of verocytotoxigeni c (VT+) Escherichia coli O157. MICs were higher for VT+ E. coli O157 t han for other strains of E. coli and for Aeromonas spp. MacConkey medi um containing sorbitol, tellurite and cefixime (TC-SMAC) permitted the growth of VT+ E. coli O157 and Shigella sonnei but partially or compl etely inhibited the growth of 67 % of other strains of E. coli and all or most strains of other sorbitol-non-fermenting species tested. Of 3 91 rectal swabs from cattle screened on TC-SMAC medium, 26 yielded iso lates of VT+ E. coli O157 whereas sorbitol-MacConkey medium with cefix ime and rhamnose yielded only nine isolates. Inclusion of potassium te llurite in sorbitol-MacConkey agar markedly increased the rate of isol ation of VT+ E. coli O157 from cattle rectal swabs and may do so for o ther types of specimen.