A Crucial Role for Exopolysaccharide Modification in Bacterial Biofilm Formation, Immune Evasion, and Virulence

Abstract

Biofilms play an important role in many chronic bacterial infections. Production of an extracellular mixture of sugar polymers called exopolysaccharide is characteristic and critical for biofilm formation. However, there is limited information about the mechanisms involved in the biosynthesis and modification of exopolysaccharide components and how these processes influence bacterial pathogenesis. Staphylococcus epidermidis is an important human pathogen that frequently causes persistent infections by biofilm formation on indwelling medical devices. It produces a poly-N-acetylglucosamine molecule that emerges as an exopolysaccharide component of many bacterial pathogens. Using a novel method based on size exclusion chromatography-mass spectrometry, we demonstrate that the surface-attached protein IcaB is responsible for deacetylation of the poly-N-acetylglucosamine molecule. Most likely due to the loss of its cationic character, non-deacetylated poly-acetylglucosamine in an isogenic icaB mutant strain was devoid of the ability to attach to the bacterial cell surface. Importantly, deacetylation of the polymer was essential for key virulence mechanisms of S. epidermidis, namely biofilm formation, colonization, and resistance to neutrophil phagocytosis and human antibacterial peptides. Furthermore, persistence of the icaB mutant strain was significantly impaired in a murine model of device-related infection. This is the first study to describe a mechanism of exopolysaccharide modification that is indispensable for the development of biofilm-associated human disease. Notably, this general virulence mechanism is likely similar for other pathogenic bacteria and constitutes an excellent target for therapeutic maneuvers aimed at combating biofilmassociated infection. Exopolysaccharide (EPS)1 is a key component of the biofilm matrix in many biofilm-forming bacteria and may be composed of various sugar polymers (1). It has an important role in immune evasion and tolerance toward antibacterial agents. By far most known EPS molecules are neutral or polyanionic (2). Enzymatic alteration of EPS is believed to significantly change its physicochemical properties and, thus, biofilm structure. However, particularly in Gram-positive bacteria, EPS-modifying enzymes and the relationship between the composition of EPS and its biological function have remained poorly characterized.The Gram-positive bacterium Staphylococcus epidermidis is the most prevalent pathogen involved in hospital-acquired infections (3). The costs related to infections caused by S. epidermidis in the hospital setting are enormous and represent a major health care burden. Most infections caused by S. epidermidis occur after the insertion of indwelling devices such as catheters or prosthetic heart valves. In these cases, the ability of S. epidermidis to form biofilms represents the most important virulence determinant (3). In a biofilm, the bacteria are dramatically less susceptible to antibiotic treatment and attacks by innate host defense. For these reasons, S. ...

The novel polysaccharide deacetylase homologue Pdi contributes to virulence of the aquatic pathogen Streptococcus iniae

“…Polysaccharide deacetylase of S. iniae intercellular adhesin (PIA) molecule. The deacetylation of PIA promotes virulence mechanisms of Staphylococcus epidermidis such as biofilm formation, surface colonization and resistance to human AMPs (Vuong et al, 2004). In S. pneumoniae and Listeria monocytogenes, mutagenesis studies have revealed that cell surface peptidoglycan deacetylaces (pgdAs) play a role in virulence (Boneca et al, 2007;Vollmer & Tomasz, 2002).…”

“…There has been a recent appreciation of the role of bacterial deacetylases in virulence. In Staphylococcus epidermidis, exopolysaccharide deacetylation has been shown to be crucial for biofilm formation, surface colonization, resistance to neutrophil phagocytosis, and resistance to cationic antimicrobial peptides (AMPs) (Vuong et al, 2004). Protection against host defences by peptidoglycan deacetylases has also been reported for Listeria monocytogenes (Boneca et al, 2007) and Streptococcus pneumoniae (Vollmer & Tomasz, 2000.…”

Yersinia pestis Biofilm in the Flea Vector and Its Role in the Transmission of Plague

“…The glycosyl transferase activity of IcaA, in conjunction with IcaD, first forms intracellular oligomers of 10-20 β-1,6-linked N-acetylglucosamine residues (Gerke et al 1998). The oligomers are then further polymerized and transported through the cell membrane via IcaC, where the polymer is partially deacylated by the polysaccharide deacetylase activity of the cell-surface protein IcaB (Vuong et al 2004a). Given the membrane localization and similar domains of the Ica, Pga, and Hms gene products, ECM biosynthesis in E. coli and Yersinia species probably proceeds by an analogous mechanism.…”

α and β Chains of Hemoglobin Inhibit Production of Staphylococcus aureus Exotoxins

“…Subsequently, the tampon sacs were removed from the test tubes, the sacs were opened with scalpel blades, and various sections of both the dialysis tubing and tampons were evaluated for CFU/ml of S. aureus and concentration of TSST-1 present. In one study, pieces of the tampons were placed in glutaraldehyde fixative with and without 0.1% methylene blue to detect biofilm formation (25) and examined by scanning electron microscopy for growth characteristics. Finally, for assays to assess the ability of α and β globin chains to inhibit exotoxin production, the following protocol was used.…”