Rapid and specific detection of F17-related pilin and adhesin genes in diarrheic and septicemic Escherichia coli strains by multiplex PCR

Abstract

The FI7-related adhesins are prevalent in Escherichia coli strains isolated from calves with diarrhea or septicemia and from lambs with nephropathy. The F17 family includes the F17a, F17b, F17c, and F111 fimbriae produced by bovine E. coli strains and the G agglutinin produced by human uropathogenic E. coli strains. An easy and inexpensive multiplex PCR method was developed to detect all the F17-related fimbriae and to identify four subtypes of structural subunit genes and two distinct subfamilies of adhesin genes by only two runs of amplification. A strict correlation was observed between the phenotypic assays and the multiplex PCR method when 166 pathogenic E. coli strains isolated from intestinal content of calves or lambs were tested. Genes encoding the F17c structural subunit and the subfamily II adhesins were prominent among bovine and ovine isolates, and the capsule-like CS31A antigen was strictly associated with the F17c fimbriae. The F17b subtype fimbriae were prominent among bovine isolates producing the CNF2 toxin, whereas the F17a subtype fimbriae were associated with the bovine isolates producing neither the CS31A antigen nor the CNF2 toxin. Five bacterial strains possessed two distinct and complete F17-related fimbrial gene clusters, and two of them produced two F17-related fimbriae at the bacterial cell surface. The related fimbrial gene clusters are probably organized in mosaic operons consisting of F17-related pilin and adhesin genes, and horizontal gene transfer may occur among E. coli strains isolated from different animal species.