The redox potential interferes with the expression of laminin binding molecules in Bacteroides fragilis

Abstract

The Bacteroides fragilis ATCC strain was grown in a synthetic media with contrasting redox potential (Eh) levels [reduced (-60 mV) Key words: Bacteroides fragilis -adhesion -redox potential -laminin binding proteins -outer membrane proteinsBacteroides fragilis is a Gram-negative obligate anaerobic bacterium and a common member of the human microbiota (Jousiemies-Somier 2002), but it is also an important opportunistic pathogen. This bacterium is the most frequently isolated anaerobic species from human intra-abdominal infections, and this represents a serious clinical problem, especially when abscesses are formed (Finegold 1995). Although several factors have been described, the pathogenicity of this microorganism is still not completely understood. The capsular polysaccharide complex (CPC) is a crucial factor in the virulence potential of the species (Comstock et al. 1999, Coyne et al. 2000. B. fragilis modulates its surface antigenicity, generating distinct CPC combinations (Krinos et al. 2001). High variation in the polysaccharide expression of B. fragilis has already been demonstrated using monoclonal antibodies (Patrick et al. 1999). Recent analyses of the genome sequences revealed DNA inversion regions. These results suggested that the ability of B. fragilis to colonise several host environments, behaving either as a member of the microbiota or a pathogen, might be linked to switching of polysaccharide biosynthesis (Krinos et al. 2001).The extracellular matrix (ECM) is a stable macromolecular structure underlying epithelial and endothelial cells and surrounding connective tissue cells. In the ECM, collagens, proteoglycans and structural glycoproteins, such as fibronectin and laminin, are found and these molecules are usually exploited for colonisation by microbes (Ljungh et al. 1996). The cell surface adhesins that mediate such recognition are termed "microbial surface components recognising adhesive matrix molecules" (MSCRAMMS). In the past, several microorganisms have been shown to express these molecules (Ljungh at al. 1996, Lähtennmaki et al. 1998, Crago & Koronakis 1999.Many bacterial virulence factors are well regulated with their expression linked to several environmental signals, such as temperature, pH, osmolarity, carbon source and iron levels (Sijbrandi et al. 2005). To the obligate anaerobic bacteria, the redox potential (Eh) represents an important environmental parameter to their survival. It has been shown that, when grown at different Eh levels, B. fragilis can change its state from commensal to pathogenic, becoming invasive to HeLa cells (Goldner et al. 1993).In the present investigation, we searched for B. fragilis properties regulated by Eh. We investigated interference with adhesion to ECM components and with the expression of proteins and surface polysaccharides. Our results showed that the adhesion to laminin is influenced by Eh, and we report that several putative binding proteins were more highly expressed under oxidising conditions by ATCC 43859 strain. MATERIAL AND METHODSBacter...

Helicobacter pylori AlpA and AlpB Bind Host Laminin and Influence Gastric Inflammation in Gerbils

“…It was later found that both Rck and a similar protein, PagC, are able to bind laminin, and their expression in Escherichia coli confers the capacity for adherence to basement membranes and host cells (11). Adherence to ECM is also believed to contribute to virulence of Bacteroides fragilis, Borrelia burgdorferi, Haemophilus influenzae, and Moraxella catarrhalis (6,18,19,53). Thus, it would not be surprising for ECM adherence by H. pylori to influence persistence or pathogenesis.…”