Abstract
Fecal samples from healthy children under 2 years of age living in Berlin, Germany (205 infants), and Melbourne, Australia (184 infants), were investigated for the presence of attaching and effacing (AE) Escherichia coli (AEEC) strains by screening for eae (intimin) genes. Twenty-seven AEEC strains were isolated from 14 children (7.6%) from Melbourne and from 12 children (5.9%) from Berlin. The 27 AEEC strains were classified as enterohemorrhagic E. coli (one strain, producing Shiga toxin 1), typical enteropathogenic E. coli (EPEC) (one strain carrying an EPEC adherence factor [EAF] plasmid), and atypical EPEC (25 strains negative for Shiga toxins and EAF plasmids). The AEEC were divided into 18 different serotypes, O-nontypeable and O-rough strains. Typing of their intimin genes revealed the presence of intimin alpha in 6 strains, intimin beta in 11 strains, intimin gamma in 7 strains, intimin zeta in 2 strains, and intimin eta in one strain. Analysis of HEp-2 cell adherence showed diffuse adherence or localized adherence-like patterns in 26 AEEC strains; local adherence was found only with the EAF-positive strain. Ten AEEC strains showed an AE property with the fluorescent actin staining (FAS) test. The introduction of an EAF plasmid (pMAR7) converted 11 FAS-negative AEEC strains to FAS positive and increased the FAS reaction in six FAS-positive AEEC strains, indicating that the genes needed for the AE phenotype were functional in these strains. Our finding indicates that atypical EPEC strains could play a double role as strains that naturally immunize against intimin in humans and as reservoirs for new emerging human pathogenic EPEC strains.
Highlights
The ability to cause attaching and effacing (AE) lesions in cells of the intestinal mucosa was identified as an important pathogenicity factor of enteropathogenic Escherichia coli (EPEC) and enterohemorrhagic E. coli (EHEC) strains [42, 64]
E. coli strains encoding intimin and other functions needed for the AE phenotype (AEEC strains) were found to be heterogeneous according to their virulence markers and human pathogenicity
Typical enteropathogenic E. coli (EPEC) strains harbor an EPEC adherence factor (EAF) plasmid which encodes functions needed for intestinal colonization and expression of the AE phenotype, whereas EHEC strains are characterized by production of Shiga toxins [42, 63]
Summary
The ability to cause attaching and effacing (AE) lesions in cells of the intestinal mucosa was identified as an important pathogenicity factor of enteropathogenic Escherichia coli (EPEC) and enterohemorrhagic E. coli (EHEC) strains [42, 64]. Intimate attachment of bacteria to the eucaryotic cell is mediated by intimin, the product of the eae gene, which is incorporated in the bacterial membrane. The detection of the intimin gene was taken as an indicator for the presence of functional LEE genes because it was shown that the presence of the eae gene correlated well with a positive FAS assay in most EPEC and EHEC isolates [34, 35, 50]. Atypical EPEC strains were described as those that carry the LEE genes but are negative for EAF plasmids, BFP, and Shiga toxin production [63]. The eae-positive E. coli strains from infants were investigated for their relationship to described EPEC and EHEC strains, for their eae gene (intimin) variants by genotyping, and for HEp-2 cell-adherence and the expression of LEE-associated genes by the FAS assay
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