Non-haemolytic and non-pigmented group b streptococcus, an infrequent cause of early onset neonatal sepsis.

The haemolysin of Group B streptococci (GBS), a leading cause of neonatal infections, is a key virulence factor that has been implicated in the development of invasive infection. The frequency of non-haemolytic (NH) GBS isolates is around 5% among GBS carriers. To determine if similar rates are observed among invasive strains, we evaluated the incidence of NH strains among 199 GBS strains isolated from neonatal blood cultures (first week of life). Overall, we found two (1%) NH strains. This finding suggests that the frequency of NH GBS strains causing early onset invasive neonatal infection is lower than the reported frequency of NH GBS among colonizing strains.

Streptolysin S of Streptococcus anginosus exhibits broad-range hemolytic activity.

Streptococcus anginosus is a commensal of mucous membranes and an emerging human pathogen. Some strains, including the type strain, display a prominent ß-hemolytic phenotype. A gene cluster (sag), encoding a variant of streptolysin S (SLS) has recently been identified as the genetic background for ß-hemolysin production in S. anginosus. In this study, we further characterized the hemolytic and cytolytic activity of the S. anginosus hemolysin in comparison with other streptococcal hemolysins. The results indicate that SLS of S. anginosus is a broad-range hemolysin able to lyse erythrocytes of different species, including horse, bovine, rabbit and even chicken. The hemolytic activity is temperature dependent, and a down-regulation of the hemolysin expression is induced in the presence of high glucose levels. Survival assays indicate that in contrast to other streptococcal species, S. anginosus does not require SLS for survival in the presence of human granulocytes. Cross-complementation studies using the sagB and sagD genes of Streptococcus pyogenes and Streptococcus dysgalactiae subsp. equisimilis demonstrated functional similarities to the S. anginosus SLS. Nevertheless, distinct differences to other streptolysin S variants were noted and provide further insights into the molecular mechanisms of SLS pathogen host interactions.