Escherichia coli O157:H7 of Genotype Lineage-Specific Polymorphism Assay 211111 and Clade 8 Are Common Clinical Isolates Within Pennsylvania

Molecular subtyping methods have previously shown that there is a nonrandom distribution of Escherichia coli O157:H7 strains among clinical and nonclinical isolates. Two examples include the lineage-specific polymorphism assay (LSPA) and clade typing assay. The clade typing method was previously used to identify a phylogenetic group of E. coli O157:H7 designated clade 8, which is believed to be more virulent than non-clade 8 isolates, and the LSPA previously indicated that clade 8 isolates are LSPA genotype 211111. Published screens have suggested that LSPA 211111 comprise anywhere from 3.9% to greater than 46% of clinical isolates. To determine the prevalence of such isolates within Pennsylvania, we applied LSPA and screened 52 clinical isolates. We found that 31% of isolates were LSPA 211111 and that 13/16 of these could be classified as clade 8. A rapid polymerase chain reaction screen for clade 8 isolates was developed and shown to have a specificity and sensitivity of 0.92 and 1.0, respectively. Polymerase chain reaction screens indicated that all isolates carried hlyA and eaeA and that all but one of the isolates carried katP. The most common LSPA genotype seen within our collection was 111111, and 29 of 30 of these carried both stx1 and stx2. Clade 8 isolates were more diverse, with four different Shiga toxin profiles observed. We conclude that E. coli O157:H7 of LSPA 211111 and clade 8 are common to clinical isolates in Pennsylvania and suggest that further studies are needed to determine whether their prevalence is increasing as observed elsewhere.