Increased EHEC survival and virulence gene expression indicate an enhanced pathogenicity upon simulated pediatric gastrointestinal conditions

Abstract : Enterohemorrhagic Escherichia coli (EHEC) are major foodborne pathogens that constitute a serious public health threat, mainly in young children. Shiga toxins (Stx) are the main virulence determinants of EHEC pathogenesis but adhesins like intimin (eae) and Long polar fimbriae (Lpf) also contribute to infection. The TNO GastroIntestinal tract Model (TIM) was used for a comparative study of EHEC O157:H7 survival and virulence under adult and child digestive conditions. Survival kinetics in the in vitro digestive tract were determined by plating while bacterial viability was assessed by flow cytometry analysis. Expression of stx, eae and lfp genes was followed by RT-qPCR and Stx production was measured by ELISA. Upon gastrointestinal passage, a higher amount of viable cells was found in the simulated ileal effluents of children compared to that of adults (with 34% and 6% of viable cells, respectively). Expression levels of virulence genes were up to 125 fold higher in children. Stx was detected only in child ileal effluents. Differences in digestive physicochemical parameters may partially explain why children are more susceptible to EHEC infection than adults. Such data are essential for a full understanding of EHEC pathogenesis and would help in designing novel therapeutic approaches.