Adherence of Glucan-Positive and Glucan-Negative Streptococcal Strains to Normal and Damaged Heart Valves

Abstract

The adherence of 18 strains of streptococci to sections of normal canine and human aortic, mitral, and tricuspid valves and to canine interatrial septum was compared in an in vitro system. Quantitative measurements of adherence ratios were performed by two independent methods. Adherence ratios for Streptococcus mutans, S. sanguis, S. bovis, and Group D streptococci were higher (0.0058-0.0101) than for the other streptococcal strains studied (0.0025-0.0041). With the exception of Group D streptococci, adherence ratios for each bacterial strain were similar with the aortic, mitral, and tricuspid valve sections. Adherence ratios with normal human and canine valve leaflets were similar, but adherence ratios with interatrial septum were lower than with normal valve sections. Adherence ratios for glucan-positive and glucan-negative strains of streptococci with normal and with damaged aortic valve leaflets were also compared. The adherence ratios of the glucan-positive streptococci (S. mutans, S. sanguis, and S. bovis) and one glucan-negative enterococcal strain (KG-3) were approximately five times higher with damaged aortic valves (0.039-0.051) than with normal aortic valves (0.009-0.010). For glucan-positive strains, adherence ratios with normal aortic leaflets were similar when bacteria were grown in media which contains or lacks sucrose. In striking contrast, growth of the glucan-positive strains in medium which lacks sucrose, with resultant deficiency of glucan production, decreased the adherence ratios with damaged aortic valve leaflets to those found with normal aortic leaflets. Treatment of glucan-positive strains with dextranase resulted in a decrease in their adherence ratios to levels seen with bacteria grown in medium lacking sucrose, but the higher adherence ratios could be restored in the presence of exogenous dextran. It is concluded that glucan production is one quantitatively important factor that contributes to the greater adherence of glucan-positive streptococci to damaged rather than to normal aortic heart valve leaflets. However, glucan production is not the only factor that determines preferential adherence of streptococci to damaged heart valves, because glucan-negative strains may also show some degree of increased adherence to damaged valves. Thus, bacterial glucan production is one of the factors that could contribute to the pathogenesis of bacterial endocarditis.