Acid and bile-salt stress of enteropathogenic Escherichia coli enhances adhesion to epithelial cells and alters glycolipid receptor binding specificity

Background. Enteropathogenic Escherichia coli (EPEC), a diarrheagenic pathogen, is exposed to stress during ingestion, and yet little is known about the impact of stress on EPEC-host cell adhesion. Methods. EPEC adhesion to human epithelial cells was assessed by plate-count assay before and after bacterial stress. Stress treatments included exposure to low pH ( with or without acid adaptation) and exposure to physiological concentrations of 4 intestinal bile salts. Expression of bacterial adhesins after stress was assessed by immunoblot and flow-cytometric analysis. Bacteria-lipid binding was determined by thin-layer chromatography overlay assay. Results. Brief low-pH stress ( with or without acid adaptation) and bile-salt stress resulted in significantly increased EPEC-host cell adhesion. Erythromycin pretreatment eliminated the adhesion enhancement, suggesting that protein synthesis was required. Immunoblot and flow-cytometric analysis indicated little change in expression of known adhesins after either stress. However, we found increased surface expression of a heat-shock protein 70 (Hsp70) on acid-shocked EPEC, and pretreatment with anti-Hsp70 eliminated the adhesion enhancement after acid stress. Acid shock also correlated with increased binding to sulfogalactosylceramide, a putative receptor for other pathogens after stress. Conclusions. Acid/bile-salt stress of EPEC significantly enhances adhesion to host cells, and a novel adhesin-receptor pair may play a role in the adhesion.