Abstract
Enteroaggregative E. coli (EAEC) are a major cause of diarrhoea worldwide. Due to their heterogeneity and carriage in healthy individuals, identification of diagnostic virulence markers for pathogenic strains has been difficult. In this study, we have determined phenotypic and genotypic differences between EAEC strains of sequence types (STs) epidemiologically associated with asymptomatic carriage (ST31) and diarrhoeal disease (ST40). ST40 strains demonstrated significantly enhanced intestinal adherence, biofilm formation, and pro-inflammatory interleukin-8 secretion compared with ST31 isolates. This was independent of whether strains were derived from diarrhoea patients or healthy controls. Whole genome sequencing revealed differences in putative virulence genes encoding aggregative adherence fimbriae, E. coli common pilus, flagellin and EAEC heat-stable enterotoxin 1. Our results indicate that ST40 strains have a higher intrinsic potential of human pathogenesis due to a specific combination of virulence-related factors which promote host cell colonization and inflammation. These findings may contribute to the development of genotypic and/or phenotypic markers for EAEC strains of high virulence.
Highlights
Enteroaggregative E. coli (EAEC) are a major cause of diarrhoea worldwide
As many of the ST31 and ST40 strains were classified as EAEC by PCR probes only, all isolates were first tested for aggregative adherence (AA) on Hep-2 cells which is the current gold-standard for the definition of the EAEC pathotype[5]
Adhesion to the intestinal mucosa is the first step in EAEC colonization of the human gut[22,26], and increased adherence of ST40 versus ST31 strains could explain the higher association of this sequence types (STs) with diarrhoeal disease
Summary
Enteroaggregative E. coli (EAEC) are a major cause of diarrhoea worldwide. Due to their heterogeneity and carriage in healthy individuals, identification of diagnostic virulence markers for pathogenic strains has been difficult. Our results indicate that ST40 strains have a higher intrinsic potential of human pathogenesis due to a specific combination of virulence-related factors which promote host cell colonization and inflammation These findings may contribute to the development of genotypic and/or phenotypic markers for EAEC strains of high virulence. AAF are encoded on the pAA virulence plasmid which contains the major transcriptional regulator AggR and the surface protein dispersin which contributes to AAF dispersal[13,14,15] Alternative adhesins such as the E. coli common pilus (ECP) can mediate aggregative adherence, in the absence of AAF16. We investigated if the association of EAEC ST40 with disease was linked to specific virulence phenotypes in vitro To this aim, we selected eight strains each of ST40 (diarrhoea-associated) and ST31 (carriage-associated) and determined aggregative adherence (AA) to intestinal epithelium, interaction with mucus, biofilm formation, cytotoxicity and stimulation of an inflammatory response. All strains were genome-sequenced, and bioinformatic analysis was used to identify putative virulence genes associated with disease potential
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