Abstract
Enterohemorrhagic E. coli (EHEC) is associated with severe gastrointestinal disease. Upon entering the gastrointestinal tract, EHEC is exposed to a fluctuating environment and a myriad of other bacterial species. To establish an infection, EHEC strains have to modulate their gene expression according to the GI tract environment. In order to explore the interspecies interactions between EHEC and an human intestinal commensal, the global gene expression profile was determined of EHEC O103:H25 (EHEC NIPH-11060424) co-cultured with B. thetaiotaomicron (CCUG 10774) or grown in the presence of spent medium from B. thetaiotaomicron. Microarray analysis revealed that approximately 1% of the EHEC NIPH-11060424 genes were significantly up-regulated both in co-culture (30 genes) and in the presence of spent medium (44 genes), and that the affected genes differed between the two conditions. In co-culture, genes encoding structural components of the type three secretion system were among the most affected genes with an almost 4-fold up-regulation, while the most affected genes in spent medium were involved in chemotaxis and were more than 3-fold up-regulated. The operons for type three secretion system (TTSS) are located on the Locus of enterocyte effacement (LEE) pathogenicity island, and qPCR showed that genes of all five operons (LEE1-LEE5) were up-regulated. Moreover, an increased adherence to HeLa cells was observed in EHEC NIPH-11060424 exposed to B. thetaiotaomicron. Expression of stx2 genes, encoding the main virulence factor of EHEC, was down-regulated in both conditions (co-culture/spent medium). These results show that expression of EHEC genes involved in colonization and virulence is modulated in response to direct interspecies contact between cells, or to diffusible factors released from B. thetaiotaomicron. Such interspecies interactions could allow the pathogen to recognize its predilection site and modulate its behaviour accordingly, thus increasing the efficiency of colonization of the colon mucosa, facilitating its persistence and increasing its virulence potential.
Highlights
The human intestinal tract is colonized by a huge number of commensal microbes and the composition and importance of this microbiota in human health and disease have been studied increasingly the last years
The growth of enterohemorrhagic E. coli (EHEC) NIPH-11060424 was inhibited at time point 4 hours when cultured in spent medium from B. thetaiotaomicron and B. fragilis, again the biological significance of this inhibition is difficult to evaluate (Fig. 1D)
The expression of EHEC NIPH-11060424 genes involved in metabolism, colonization and virulence is modulated in response to direct contact with B. thetaiotaomicron and to soluble factors released from B. thetaiotaomicron
Summary
The human intestinal tract is colonized by a huge number of commensal microbes and the composition and importance of this microbiota in human health and disease have been studied increasingly the last years. The intestinal microbiota plays an important role as a protective barrier against pathogenic microorganisms by competing for nutrition and attachment sites on the epithelium, boosting the host’s gut- and systemic immune response, and producing various antibacterial substances [3]. To overcome this hurdle, enteric pathogens must have mechanisms to interact and cope with the resident microbial community and with numerous host- and environmentally derived stressors that affect their functionality and pathogenic processes. The overall gene expression profile of an EHEC in co-culture with the predominant human commensal B. thetaiotaomicron has, to our knowledge, not been explored
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