Exopolysaccharide production by viridans streptococci in experimental endocarditis

Abstract

Light and electron microscopy with histochemical staining were used to estimate exopolysaccharide production by strains of viridans streptococci recovered from patients with endocarditis. Six strains were selected for study because they represented a wide range of in vitro polysaccharide production. By light microscopy, there was good agreement between three polysaccharide stains (ruthenium red, periodic acid-Schiff and calcifluor white) in the amount of glycocalyx produced, which ranged from minimal (0 to 1+) to maximal amounts (4+). Two strains selected for minimal (strain 1) and maximal (strain 6) in vitro exopolysaccharide production were studied after we used them to experimentally infect cardiac vegetations. Glycocalyx could be demonstrated surrounding organisms in cardiac vegetations, and the relative amounts produced were similar to those seen in vitro. Vegetations formed by glycocalyx-producing strains were also larger than those formed by glycocalyx-deficient strains. Viridans group streptococci which produce exopolysaccharide in vitro also do so within cardiac vegetations. The relationship of exopolysaccharide production to maintenance of endocardial infection is discussed.on August 4, 2020 by guest

Effects of alginase on the natural history and antibiotic therapy of experimental endocarditis caused by mucoid Pseudomonas aeruginosa

“…EM. After removal from the valve, vegetations were placed in a 1:1 dilution of mouse antialginate monoclonal antibody in 0.1% bovine serum albumin for 1 h at room temperature to stabilize the glycocalyx for transmission electron microscopy (EM) (14,16); ruthenium red was used as the glycocalyx stain for these experiments (15). Specimens were washed three times in cacodylate buffer and then fixed in 2% gluteraldehyde containing 0.08% ruthenium red for 6 h. The vegetations were washed in buffer containing 0.5% ruthenium red and then postfixed in osmium tetroxide containing 0.5% ruthenium red at room temperature.…”

“…Ultrastructural evaluation of intravegetation pseudomonal cells was performed only on organisms which were intact and unphagocytized by PMNs. The cell surfaces of the intravegetation organisms were examined for ruthenium red-stained, electron-dense flocculant and fibrillar material surrounding the cell membrane, which represents the glycocalyx (14,16). EM of vegetations infected with mucoid strain 144MR revealed bacterial cells surrounded by an electron-dense glycocalyx distributed in a patchy fashion around the cell membrane and extending into the intracellular area between adjacent organisms (Fig.…”

Some bacterial parameters influencing the neutrophil oxidative burst response to Pseudomonas aeruginosa biofilms

“…In recent years the persistence of the bacteria has been increasingly attributed to the concept of bacterial biofilms (5,7). The capability of bacteria to establish themselves in microcolonies or biofilms, where they are enmeshed in glycocalyx and escape elimination by host defenses as well as by antibiotics, has been documented in clinical cases and under experimental conditions (4,16,24,(27)(28)(29)34). The mechanisms of antibiotic resistance of these sessile bac-teria are currently being investigated (2,12,15,19), as are the mechanisms by which they escape host defenses (21,39).…”

Association of Novel Streptococcus sanguinis Virulence Factors With Pathogenesis in a Native Valve Infective Endocarditis Model

“…Cardiac vegetations, which develop over the course of IE, are considered biofilm-like structures composed of both bacterial and host factors (Elgharably et al, 2016). While in vitro biofilm formation on a plastic surface does not strongly correlate with in vivo virulence (Ge et al, 2008;Leuck et al, 2014), production of an extracellular matrix has been described to occur within streptococcal vegetations (Mills et al, 1984) and production of extracellular polysaccharide (EPS) correlates with streptococcal IE (Mills et al, 1984;Dall and Herndon, 1990). Consistent with a previous report (Ge et al, 2008), supplementation with the same concentration of glucose, a more physiologically relevant sugar, did not produce strong biofilms in this assay (data not shown).…”