Abstract
BackgroundAfter uropathogenic Escherichia coli (UPEC), Enterococcus faecalis is the second most common pathogen causing urinary tract infections. Monoglucosyl-diacylglycerol (MGlcDAG) and diglucosyl-diacylglycerol (DGlcDAG) are the main glycolipids of the E. faecalis cell membrane. Examination of two mutants in genes bgsB and bgsA (both glycosyltransferases) showed that these genes are involved in cell membrane glycolipid biosynthesis, and that their inactivation leads to loss of glycolipids DGlcDAG (bgsA) or both MGlcDAG and DGlcDAG (bgsB). Here we investigate the function of bgsB and bgsA regarding their role in the pathogenesis in a mouse model of urinary tract infection and in bacterial adhesion to T24 bladder epithelial cells.ResultsIn a mouse model of urinary tract infection, we showed that E. faecalis 12030ΔbgsB and E. faecalis 12030ΔbgsA mutants, colonize uroepithelial surfaces more efficiently than wild-type bacteria. We also demonstrated that these mutants showed a more than three-fold increased binding to human bladder carcinoma cells line T24 compared to the wild-type strain. Bacterial binding could be specifically inhibited by purified glycolipids. Lipoteichoic acid (LTA), wall-teichoic acid (WTA), and glycosaminoglycans (GAGs) were not significantly involved in binding of E. faecalis to the bladder epithelial cell line.ConclusionsOur data show that the deletion of bgsB and bgsA and the absence of the major glycolipid diglucosyl-diacylglycerol increases colonization and binding to uroepithelial cells. We hypothesize that secreted diglucosyl-diacylglycerol blocks host binding sites, thereby preventing bacterial adhesion. Further experiments will be needed to clarify the exact mechanism underlying the adhesion through glycolipids and their cognate receptors.
Highlights
Urinary tract infections (UTIs) are the most common bacterial infection in the inpatient and outpatient setting, leading to about 8.6 million patient visits in the United States in 2007 [1,2,3]
These mutants showed a more than three-fold increased binding (2.66106 colony-forming units (CFUs)/mL and 2.36106 CFU/mL) to the T24 human bladder carcinoma cell line compared to wild-type bacteria (0.76106 CFU/mL, Figure 1A)
The increased attachment was significantly lower with the complemented strains of both mutants E. faecalis 12030DbgsB rec and E. faecalis 12030DbgsA rec (1.16106 CFU/mL and 0.86106 CFU/mL, Figure 1A)
Summary
Urinary tract infections (UTIs) are the most common bacterial infection in the inpatient and outpatient setting, leading to about 8.6 million patient visits in the United States in 2007 [1,2,3]. Urinary tract infection caused by E. faecalis is the most common enterococcal infection, and after uropathogenic Escherichia coli (UPEC), enterococci are the second most common organisms responsible and the most common gram-positive urinary pathogen [6]. Despite their important role in the pathophysiology of urinary tract infections, the molecular mechanisms of colonization and infection are still not well understood. After uropathogenic Escherichia coli (UPEC), Enterococcus faecalis is the second most common pathogen causing urinary tract infections. We investigate the function of bgsB and bgsA regarding their role in the pathogenesis in a mouse model of urinary tract infection and in bacterial adhesion to T24 bladder epithelial cells
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