Prevalence of fimbrial adhesins-encoding genes of diarrheagenic Escherichia coli in atypical enteropathogenic E. coli strains

BM10

Natália Cristina de Freitas (nataliacf@butantan.gov.br); Julia Mitico Nara; Waldir Pereira Elias Junior; Roxane Maria Fontes Piazza.

Laboratório de Bacteriologia, Instituto Butantan, SP, Brasil

Diarrheagenic E. coli is classified into six main pathotypes: enteropathogenic E. coli (EPEC), enterohemorrhagic E. coli, enterotoxigenic E. coli (ETEC), enteroaggregative E. coli (EAEC), diffusely adherent E. coli and enteroinvasive E. coli. Among these pathotypes, EPEC and the EAEC are subdivided in typical and atypical. EPEC is identified on the presence of eae and bfpA genes that encode the adhesin intimin and the type IV pili BFP, respectively. Both genes are used for classification of EPEC in two groups: typical (eae+/bfpA+) and atypical (eae+/bfpA-). Current data demonstrate that atypical EPEC (aEPEC) are more prevalent than typical EPEC, either in developed or developing countries. Adhesion, an essential first step in bacterial pathogenesis, is mediated by adhesins, and is critical for successful E. coli colonization of host’s mucosa. The distinct surface structures can be divided into fimbrial and non-fimbrial adhesins. The objective was to investigate the prevalence of genes that encode fimbrial components described in some pathotypes of E. coli among 76 isolates of atypical EPEC. The PCR technique was employed to search for the presence of the gene sequences in 76 strains of atypical EPEC isolated form cases of acute diarrhea: fimA, fimH, lpfaO113, cs3, cs4 and cs6. These gene sequences correspond to the type I fimbriae of Enterobacteriaceae (fimA and fimH), long polar fimbriae of Shiga toxin-producing E. coli (STEC) of serogroup O113 (lpfAO113) and the CS3, CS4 and CS6 colonization factors of ETEC. The PCR reactions were developed employing specific primers based on published sequences to amplify the amplicons: fimA - 161 bp, fimH - 508 bp, lpfaO113 - 573 bp, cs3 - 264 bp, cs4 - 250 bp, cs6 - 261 bp. The genes fimA and fimH were found in 75 (94.7%) and 77 (97.4%) isolates, respectively. Regarding the lpfAO113 gene sequence, 16 (21%) of the isolates harbored that sequence. None of the isolates presented the cs3, cs4 and cs6 genes. The absence of genes encoding colonization factors of ETEC among atypical EPEC suggests that these structures are not spread among other pathotypes of E. coli and that their encoding genes do not suffer horizontal transfer. The detection of lpfaO113 gene, originally described in isolates of STEC belonging to the serogroup O113, in atypical EPEC strains corroborates the proposal phylogenetic relationship between atypical EPEC and STEC. The high prevalence of fimA and fimH genes were expected since they encode the type I fimbriae, a common structure in E. coli. The role of these fimbrial structures in atypical EPEC pathogenesis is unclear.