RESUMEN
The O26 serogroup of enteropathogenic Escherichia coli (EPEC) is one of the serogroups most frequently implicated in infant diarrhea and is also common among enterohemorrhagic E. coli (EHEC) strains. The most common O26 strains belong to EPEC/EHEC serotype O26:H11 and are generally Shiga toxin (Stx) positive. Stx-negative E. coli strains that are negative for the EPEC EAF plasmid and bundle-forming pilus (Bfp) are classified as atypical EPEC. Here, we report a novel adhesin present in an stx-negative bfpA-negative atypical EPEC O26:H11 strain isolated from an infant with diarrhea. A cloned 15-kb genomic region from this strain, designated the locus for diffuse adherence (lda), confers diffuse adherence on HEp-2 cells when expressed in E. coli K-12. Sequence analysis of lda revealed a G+C content of 46.8% and 15 open reading frames sharing homology with the E. coli K88 fae and CS31A clp fimbrial operons. The lda region is part of a putative 26-kb genomic island inserted into the proP gene of the E. coli chromosome. Hybridization studies have demonstrated the prevalence of the minor structural subunit gene, ldaH, across E. coli serogroups O5, O26, O111, and O145. A second plasmid-encoded factor that contributed to the Hep-2 adherence of this strain was also identified but was not characterized. Null mutations that abolish adherence to HEp-2 cells can be restored by plasmid complementation. Antiserum raised against the major structural subunit, LdaG, recognizes a 25-kDa protein from crude heat-extracted protein preparations and inhibits the adherence of the E. coli DH5alpha lda(+) clone to HEp-2 cells. Electron microscopy revealed a nonfimbrial structure surrounding the bacterial cell.
Asunto(s)
Adhesinas de Escherichia coli/genética , Escherichia coli/genética , Adhesinas de Escherichia coli/inmunología , Secuencia de Aminoácidos , Antígenos Bacterianos/genética , Adhesión Bacteriana/inmunología , Escherichia coli/inmunología , Escherichia coli/patogenicidad , Proteínas de Escherichia coli/genética , Proteínas Fimbrias/genética , Inmunohistoquímica , Microscopía Electrónica , Datos de Secuencia Molecular , Alineación de Secuencia , Análisis de Secuencia de ADNRESUMEN
The virulence profiles of most atypical enteropathogenic Escherichia coli (EPEC) strains are unknown. A total of 118 typical and atypical strains of EPEC serotypes and non-EPEC serogroups isolated from children with or without acute diarrhea who were from different cities in Brazil were examined for virulence-associated markers and adherence to HEp-2 cells, and also had random amplified polymorphic DNA (RAPD) analysis performed. Atypical strains were identical to typical strains with regard to the virulence factors encoded on the locus of enterocyte effacement (LEE). In contrast with typical EPEC strains, none of the atypical strains reacted with the bfpA probe, and half of the strains hybridized with the perA probe. Most atypical strains presented Tir sequences that correlated with enteropathogenic or enterohemorrhagic E. coli (98%), had LEE inserted in either selC or pheU (88%), and presented a typeable intimin (52%). Eighteen new serotypes were found in the EPEC strains. Atypical and typical EPEC strains belonged to different RAPD clusters. Most atypical strains showed a localized-like adherence pattern (61.5%). Of the non-LEE-encoded virulence factors, enteroaggregative E. coli heat-stable enterotoxin was noted most frequently (45%) and was significantly associated with diarrhea (P=.01). Thus, this virulence marker may be used as an additional tool for the diagnosis of truly atypical pathogenic strains.