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 orga nisms associated with severe gastrointestinal and systemic diseases in huma ns, Within the STEC family, eae-positive STEC strains, particularly those b elonging to serogroups O157 and O111, appear to have greater virulence for humans. However, in spite of being ene negative, STEC strains belonging to serogroup O113 have frequently been associated with cases of severe STEC di sease, including hemolytic-uremic syndrome (I-IUS). We have de, eloped a mo dified multiplex PCR assay for detection of STEC strains belonging to these three serogroups in cultures of feces by using primers specific for portio ns of the genetic loci (rfb) encoding biosynthesis of the respective O anti gen. These primers direct amplification of PCR products of 259, 406, and 59 3 bp for serogroups O157, O111, and O113, respectively. The assay was valid ated by testing 40 previously characterized STEC strains, with 100% agreeme nt, It also detected STEC strains of the appropriate genotype in primary fe cal cultures from 13 patients with HUS or bloody diarrhea, Thirty other pri mary fecal cultures from patients without evidence of STEC infection were n egative.