Abstract
Enterococcus faecalis is considered a leading cause of hospital-acquired infections. Treatment of these infections has become a major challenge for clinicians because some E. faecalis strains are resistant to multiple clinically used antibiotics. Moreover, the presence of E. faecalis biofilms can make infections with E. faecalis more difficult to eradicate with current antibiotic therapies. Thus, our aim in this study was to investigate the effects of probiotic derivatives against E. faecalis biofilm formation. Bacillus subtilis natto is a probiotic strain isolated from Japanese fermented soybean foods, and its culture fluid potently inhibited adherence to Caco-2 cell monolayers, aggregation, and biofilm production without inhibiting the growth of E. faecalis. An apparent decrease in the thickness of E. faecalis biofilms was observed through confocal laser scanning microscopy. In addition, exopolysaccharide synthesis in E. faecalis biofilms was reduced by B. subtilis natto culture fluid treatment. Carbohydrate composition analysis also showed that carbohydrates in the E. faecalis cell envelope were restructured. Furthermore, transcriptome sequencing revealed that the culture fluid of B. subtilis natto downregulated the transcription of genes involved in the WalK/WalR two-component system, peptidoglycan biosynthesis and membrane glycolipid biosynthesis, which are all crucial for E. faecalis cell envelope synthesis and biofilm formation. Collectively, our work shows that some derivatives present in the culture fluid of B. subtilis natto may be useful for controlling E. faecalis biofilms.
Highlights
Enterococci, which are Gram-positive bacteria normally present in human gastrointestinal tracts, are the second most common pathogens recovered from catheter-associated infections of the bloodstream and urinary tract and from skin and soft-tissue infections in hospitals in the United States (Paulsen et al, 2003; Arias and Murray, 2012)
To test our hypothesis that B. subtilis natto supernatant would interfere with E. faecalis biofilm formation, we first investigated whether the ability of E. faecalis to adhere onto the human intestinal epithelial cell line Caco-2 was inhibited by B. subtilis natto supernatant treatment
The relative adhesion of E. faecalis OG1RF (WT) cells decreased from 1.55 to 1.02%; the relative adhesion of E. faecalis OG1RF::p23cfp cells decreased from 0.93 to 0.51% (Figures 1B,D). These results indicated that B. subtilis natto supernatant likely interferes with the ability of E. faecalis to adhere to host tissues, such as the human intestinal tract
Summary
Enterococci, which are Gram-positive bacteria normally present in human gastrointestinal tracts, are the second most common pathogens recovered from catheter-associated infections of the bloodstream and urinary tract and from skin and soft-tissue infections in hospitals in the United States (Paulsen et al, 2003; Arias and Murray, 2012). In addition to having intrinsic resistance to multiple antibiotics and the ability to transfer antibiotic resistance via plasmid transfer, E. faecalis can readily form biofilms on a wide range of natural and artificial substrates, such as damaged heart valves, venous catheters, urinary catheters, and indwelling medical devices (Donlan and Costerton, 2002; Fernandez Guerrero et al, 2007). Since the protective extracellular matrix can decrease the penetration of antibiotics, E. faecalis cells in biofilms can be 10 to 1,000 times more resistant to antibiotics than their planktonic counterparts (Hoyle and Costerton, 1991; Mah and O’Toole, 2001). This trait of enterococcal biofilms markedly reduces the effectiveness of current antibiotic treatments. There is a demand for novel, safe, and effective methods to inhibit the formation of E. faecalis biofilms
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