Direct Detection of Shiga Toxigenic Escherichia coli Strains Belonging to Serogroups O111, O157, and O113 by Multiplex PCR

Shiga toxigenic Escherichia coli (STEC) strains are a diverse group of organisms associated with severe gastrointestinal and systemic diseases in humans. Within the STEC family, eae-positive STEC strains, particularly those belonging to serogroups O157 and O111, appear to have greater virulence for humans. However, in spite of being eae negative, STEC strains belonging to serogroup O113 have frequently been associated with cases of severe STEC disease, including hemolytic-uremic syndrome (HUS). We have developed a modified multiplex PCR assay for detection of STEC strains belonging to these three serogroups in cultures of feces by using primers specific for portions of the genetic loci (rfb) encoding biosynthesis of the respective O antigen. These primers direct amplification of PCR products of 259, 406, and 593 bp for serogroups O157, O111, and O113, respectively. The assay was validated by testing 40 previously characterized STEC strains, with 100% agreement. It also detected STEC strains of the appropriate genotype in primary fecal cultures from 13 patients with HUS or bloody diarrhea. Thirty other primary fecal cultures from patients without evidence of STEC infection were negative.