title: Bicarbonate ion stimulates the expression of locus of enterocyte effacement-encoded genes in enterohemorrhagic Escherichia coli O157:H7.
abstract: Enterohemorrhagic Escherichia coli (EHEC) strains adhere to the intestinal mucosa and produce an attaching and effacing (A/E) lesion. Most of the genes required to produce A/E lesions are thought to be encoded by the 36-kb pathogenicity island termed the locus for enterocyte effacement (LEE). Although the mechanisms underlying the bacterial adherence, including the genes involved, are still poorly understood, the preferential adherence phenotype of EHEC is thought to depend on the nature of the genes and/or the response of these genes to changes in environmental conditions. To explore the environmental factors affecting EHEC adherence, we used an O157:H7 strain and investigated the optimal growth conditions for its adherence to Caco-2 cells. We observed that EHEC grown in Dulbecco's modified Eagle's medium (DMEM) adhered more efficiently to Caco-2 cells than EHEC grown in Luria-Bertani (LB) broth. Among the components of DMEM, only NaHCO(3) was found to remarkably stimulate bacterial adherence. When bacteria were grown in LB broth containing NaHCO(3), the production of intimin, Tir, EspA, and EspB was greatly enhanced compared with the production in LB broth. Indeed, the transcription of ler required for LEE-encoded gene expression was promoted in response to the concentration of NaHCO(3) in LB broth. Since the concentration of NaHCO(3) in the lower intestinal tract has been shown to be relatively high compared with that in the upper small intestine, our results may imply that NaHCO(3) is an important signaling factor for promoting colonization of EHEC in the lower intestinal tract in humans.
authors.affiliation: Department of Microbiology and Immunology, Institute of Medical Science, University of Tokyo, Minato-ku, Tokyo 108-8639, Japan.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Abe
authors.forename: Ichiro
authors.initials: I
authors.lastname: Tatsuno
authors.forename: Toru
authors.initials: T
authors.lastname: Tobe
authors.forename: Akiko
authors.initials: A
authors.lastname: Okutani
authors.forename: Chihiro
authors.initials: C
authors.lastname: Sasakawa
mesh_terms: D001422:Bacterial Adhesion; D001639:Bicarbonates / Q000494:pharmacology*; D018938:Caco-2 Cells; D003470:Culture Media; D020895:Enterocytes; D019453:Escherichia coli O157 / Q000187:drug effects* / Q000235:genetics / Q000254:growth & development / Q000502:physiology; D029968:Escherichia coli Proteins / Q000235:genetics*; D015870:Gene Expression / Q000187:drug effects*; D005798:Genes, Bacterial; D006801:Humans; D007477:Ions; D010750:Phosphoproteins
chemical_list: D001639:Bicarbonates; D003470:Culture Media; D029968:Escherichia coli Proteins; D007477:Ions; C457340:LEE protein, E coli; D010750:Phosphoproteins