Abstract
Enteroaggregative Escherichia coli (EAEC) is a significant cause of diarrhoeal illness in both children and adults. Genetic heterogeneity and recovery of EAEC strains from both healthy and diseased individuals complicates our understanding of EAEC pathogenesis. We wished to establish if genetic or phenotypic attributes could be used to distinguish between strains asymptomatically colonising healthy individuals and those which cause disease. Genotypic screening of a collection of twenty four EAEC isolates from children with and without diarrhoea revealed no significant differences in the repertoire of putative virulence factors present in either group of strains. In contrast, EAEC strains from phylogroup A were more strongly associated with asymptomatic groups whereas strains from phylogroup D were more associated with cases of diarrhoea. Phenotypic screening revealed no differences in the ability of strains from either cohort of children to form biofilms, to adhere to and invade cells in tissue culture or to cause disease in the Caenorhabditis elegans model of infection. However, the latter assay did reveal significant reduction in nematode killing rates when specific virulence factors were deleted from human pathogenic strains. Our results suggest that current models of infection are not useful for distinguishing avirulent from pathogenic strains of EAEC but can be useful in studying the effect of specific virulence factors.
Highlights
Based on genotypic and phenotypic traits diarrhoeagenic Escherichia coli can be categorised into six different pathotypes: enteroaggregative E. coli (EAEC), enterotoxigenic E. coli (ETEC), enteroinvasive E. coli (EIEC), enteropathogenic E. coli (EPEC), enterohaemorrhagic E. coli (EHEC) and diffuse-adhering E. coli (DAEC)
The EAEC strains used in this study were previously identified from a large screen of 150 children aged less than two years old with acute diarrhoea and 50 age-matched healthy controls [25]
To determine if EAEC virulence factors were more associated with strains from cases than from controls we tested each strain by PCR for the presence of 17 genes previously associated with EAEC virulence including the virulence regulator aggR, fimbrial genes, iron uptake genes, genes encoding Type 6 secretion system (T6SS)-related proteins and genes encoding autotransporters of the SPATE subfamily (Table 1) [26]
Summary
Based on genotypic and phenotypic traits diarrhoeagenic Escherichia coli can be categorised into six different pathotypes: enteroaggregative E. coli (EAEC), enterotoxigenic E. coli (ETEC), enteroinvasive E. coli (EIEC), enteropathogenic E. coli (EPEC), enterohaemorrhagic E. coli (EHEC) and diffuse-adhering E. coli (DAEC). The pAA plasmids carry many factors associated to EAEC pathogenesis, including the heatstable toxin-1 (EAST-1) [7], fimbrial adhesins (AAF/I, II, III and IV), aatA (which corresponds to CVD432 fragment) encoding an outer-membrane protein TolC, which is a component of the aatencoded ABC transporter involved in secretion of dispersin [1]. Adhesins, toxins and several other factors delivered by a type V secretion system (T5SS) or type VI secretion system (T6SS) have been implicated in pathogenesis [9,10,12,13,14] None of these factors has been consistently associated with EAECmediated disease and none of these factors are found in all EAEC strains
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