Identification of Sequence Diversity in the Escherichia coli fliC Genes Encoding Flagellar Types H8 and H40 and Its Use in Typing of Shiga Toxin-Producing E. coli O8, O22, O111, O174, and O179 Strains

Abstract

ABSTRACT Flagellar type H8 is associated with many strains of pathogenic Shiga toxin-producing Escherichia coli (STEC), such as O8, O22, O111, O174, and O179 strains. Serological typing of the H8 antigen is limited to motile strains only and suffers from cross-reactivity between flagellar H8 and H40 antigens. In order to develop a method useful for typing of motile and nonmotile STEC O111 and other strains, we have analyzed the flagellar antigen ( fliC ) genes in representative E. coli H8 and H40 types. Two genotypes of the fliC gene encoding H8 (the fliC -H8 gene) were identified. Genotype fliC -H8a was found to be conserved in STEC O111, O174, and O179 strains; and type fliC -H8b was associated with STEC O8 and O22 strains. Sequence variations were also found in the genetically closely related fliC -H40 gene, although the latter was not found to be associated with STEC strains. A PCR was developed for the specific identification of the fliC -H8 and the fliC -H40 genes in motile and nonmotile E. coli strains. Digestion of PCR products with HhaI resulted in restriction fragment length polymorphisms (RFLPs) which were associated with genotypes fliC -H8a and -H8b as well as with genotypes fliC -H40a and -H40b. The fliC -specific PCR/RFLP typing method was suitable for the rapid typing of motile and nonmotile STEC O8, O22, O111, O174, and O179 strains from different sources whose fliC -H8 genotypes were found to be highly conserved. The fliC genotyping method is advantageous over serotyping and is useful for epidemiological investigations and studies of the evolution of STEC clones.