Bile salts induce expression of the afimbrial LDA adhesin of atypical enteropathogenic Escherichia coli

Abstract

SummaryAtypical enteropathogenic Escherichia coli (aEPEC) strains are frequently implicated in infant diarrhoea in developing countries. Not much is known about the adherence properties of aEPEC; however, it has been shown that these strains can adhere to tissuecultured cells. A chromosomal region designated the locus for diffuse adherence (LDA) confers aEPEC strain 22 the ability to adhere to culture cells. LDA is an afimbrial adhesin that contains a major subunit, LdaG, whose expression is induced on MacConkey agar at 37°C. We hypothesized that the bile salts found in this culture media induce the expression of LdaG. Strain 22 and the LdaG mutant were grown in Luria-Bertani (LB) media in the presence or absence of bile salts and heat-extracted surface-expressed proteins were separated by SDS-PAGE to determine whether expression of the 25 kDa LdaG protein was induced. Western blot analysis with anti-LdaG confirmed that bile salts enhance LdaG expression at 37°C. Adhesion assays on HeLa cells revealed that adhesion in a diffuse pattern of strain 22 increased in the presence of bile salts. We also confirmed that expression of the localized adherence pattern observed in the ldaG mutant required the presence of a large cryptic plasmid found in strain 22 and that this phenotype was not induced by bile salts. At the transcriptional level, the ldaG-lacZ promoter fusion displayed maximum beta-galactosidase activity when the parent strain was grown in LB supplemented with bile salts. Fluorescence Activated Cell Sorting analysis, immunogold labelling electron microscopy and immunofluorescence using antiLdaG sera confirmed that LDA is a bile saltsinducible surface-expressed afimbrial adhesin. Finally, LdaG expression was induced in presence of individual bile salts but not by other detergents. We concluded that bile salts increase expression of LDA, conferring a diffuse adherence pattern and having an impact on the adhesion properties of this aEPEC strain.

Proteins differentially expressed by Shiga toxin-producing Escherichia coli strain M03 due to the biliar salt sodium deoxycholate

“…It was found that in response to bile E. coli is able to actively pump out bile salts through the efflux system AcrAB, thus limiting the toxic action of these compounds (Thanassi et al, 1997). In the diarrheagenic strains of E. coli, enteropathogenic E. coli (EPEC) and atypical enteropathogenic E. coli (aEPEC) bile salt stress resulted in an increase in adhesion of bacteria to human epithelial cells (de Jesus et al, 2005;Torres et al, 2007). Microarray analysis of STEC 0157:H7 indicated that the presence of bile salts resulted in protective alterations of the outer membrane, downregulating the expression of OmpF porin, through which bile pass into the periplasm of E. coli, and upregulating the efflux pump AcrA-AcrB, thereby limiting the toxic effects on the bacteria.…”

Identification of Coli Surface Antigen 23, a Novel Adhesin of Enterotoxigenic Escherichia coli

“…Protein heat extraction is a procedure that has been used to identify some CFs in ETEC strains and other adhesins in pathogenic E. coli strains under different environmental conditions (21,34). We used this approach to obtain proteins from ETEC 1766a cultured at 20°C and 37°C, which were then separated by SDS-PAGE.…”

Survival of the Fittest: How Bacterial Pathogens Utilize Bile To Enhance Infection

“…These signals include factors that facilitate gastrointestinal adherence of the bacteria to the small intestinal or colonic epithelial cells (17,19). Studies investigating bile responses in E. coli include both commensals and diarrheagenic pathovars, including enteropathogenic E. coli (EPEC), enterotoxigenic E. coli (ETEC), and enterohemorrhagic E. coli (EHEC) (20)(21)(22)(23)(24)(25)(26)(27)(28). …”