Genetic transformation in Streptococcus sanguis. Identification, surface spreading and competence of invasive strains of Streptococcus sanguis Lancefield groups H and W and other invasive viridans streptococci

Abstract

Of 46 viridans streptococci isolated from cases of probably true bacteremia, 26 strains or 56% could be grouped serologically in the Lancefield system. Eight strains (17%) were identified as serogroup H (characteristic of Streptococcus sanguis), ten strains (22%) as serogroup W (a new group antigen found in S. sanguis) and eight strains (17%) as serogroup K (related to S. mitis (mitior)). The high number of serogroupable viridans streptococci was specially due to the introduction of serogroup W and indicates the importance of this serogroup in cases of bacteremia. A set of six diagnostic tests (production of hydrogen peroxide, arginine and esculin hydrolysis, polysaccharide production, Voges-Proskauer reaction, mannitol fermentation) was used for speciation of the viridans streptococci; in addition, search for spreading zones around the colonies was included in the diagnostic procedure. Spreading zones were only present in S. sanguis and occurred more frequently in group H strains than group W strains. The 46 viridans streptococci were tested in genetic transformation. The prevalence of spontaneous competence in strains isolated from the blood was high, particularly in S. sanguis serogroup H (88%) and W (50%). For serogroup H, spontaneous competence was found as frequently among invasive strains as among carrier isolates previously studied.