ABSTRACT
Enteropathogenic Escherichia coli (EPEC) forms attaching and effacing lesions in the intestinal mucosa characterized by intimate attachment to the epithelium by means of intimin (an outer membrane adhesin encoded by eae). EPEC is subgrouped into typical (tEPEC) and atypical (aEPEC); only tEPEC carries the EAF (EPEC adherence factor) plasmid that encodes the bundle-forming pilus (BFP). Characteristically, after 3 h of incubation, tEPEC produces localized adherence (LA) (with compact microcolonies) in HeLa/HEp-2 cells by means of BFP, whereas most aEPEC form looser microcolonies. We have previously identified nine aEPEC strains displaying LA in extended (6 h) assays (LA6). In this study, we analysed the kinetics of LA6 pattern development and the role of intimin in the process. Transmission electron microscopy and confocal laser microscopy showed that the invasive process of strain 1551-2 displays a LA phenotype. An eae-defective mutant of strain 1551-2 prevented the invasion although preserving intense diffused adherence. Sequencing of eae revealed that strain 1551-2 expresses the omicron subtype of intimin. We propose that the LA phenotype of aEPEC strain 1551-2 is mediated by intimin omicron and hypothesize that this strain expresses an additional novel adhesive structure. The present study is the first to report the association of compact microcolony formation and an intense invasive ability in aEPEC.
Subject(s)
Adhesins, Bacterial/physiology , Bacterial Adhesion/physiology , Enteropathogenic Escherichia coli/pathogenicity , Escherichia coli Proteins/physiology , Actins/metabolism , Adhesins, Bacterial/chemistry , Amino Acid Sequence , Enteropathogenic Escherichia coli/genetics , Enteropathogenic Escherichia coli/ultrastructure , Escherichia coli Proteins/chemistry , Escherichia coli Proteins/metabolism , HeLa Cells , Humans , Microscopy, Electron, Transmission , Molecular Sequence Data , Phenotype , Phosphorylation , Receptors, Cell Surface/metabolism , Sequence AlignmentABSTRACT
The characterization of nine atypical enteropathogenic Escherichia coli strains expressing localized adherence in HeLa cells in the absence of the bundle-forming pilus revealed a diversity of serotypes, plasmids, and virulence genes. Although the strains lacked known E. coli adhesin genes, the identification of new adhesins could contribute to the characterization of similar enteropathogenic E. coli isolates.
