Multiplex PCR for detection of the heat-labile toxin gene and shiga-like toxin I and II genes in Escherichia coli isolated from natural waters.

A triplex PCR method was developed to simultaneously amplify a heat-labile toxin sequence (LT) of 258 bp, a shiga-like toxin I sequence (SLT I) of 130 bp, and a shiga-like toxin II sequence (SLT II) of 346 bp from toxigenic strains of Escherichia coli. This method was used to screen 377 environmental E. coli isolates from marine waters or estuaries located in Southern California and North Carolina for enterotoxigenic or enterohemorrhagic E. coli strains. Of the 377 E. coli screened, one isolate was found to belong to the enterotoxigenic group, since it contained a LT homologous sequence, and one isolate was found to belong to the enterohemorrhagic group, since it contained a SLT I homologous sequence. None was found to contain SLT II homologous sequences. The pathogenicity of the positive environmental E. coli isolates was confirmed by standard bioassays with Y-1 adrenal cells and Vero cells to confirm toxin production. Our results suggest that toxigenic E. coli occurs infrequently in environmental waters and that there is a low public health risk from toxigenic E. coli in coastal waters.