Sword and shield: linked group B streptococcal β-hemolysin/cytolysin and carotenoid pigment function to subvert host phagocyte defense

GY Liu, KS Doran, T Lawrence… - Proceedings of the …, 2004 - National Acad Sciences
GY Liu, KS Doran, T Lawrence, N Turkson, M Puliti, L Tissi, V Nizet
Proceedings of the National Academy of Sciences, 2004National Acad Sciences
Group B Streptococcus (GBS) is a major cause of pneumonia, bacteremia, and meningitis in
neonates and has been found to persist inside host phagocytic cells. The pore-forming GBS
β-hemolysin/cytolysin (βH/C) encoded by cylE is an important virulence factor as
demonstrated in several in vivo models. Interestingly, cylE deletion results not only in the
loss of βH/C activity, but also in the loss of a carotenoid pigment of unknown function. In this
study, we sought to define the mechanism (s) by which cylE may contribute to GBS …
Group B Streptococcus (GBS) is a major cause of pneumonia, bacteremia, and meningitis in neonates and has been found to persist inside host phagocytic cells. The pore-forming GBS β-hemolysin/cytolysin (βH/C) encoded by cylE is an important virulence factor as demonstrated in several in vivo models. Interestingly, cylE deletion results not only in the loss of βH/C activity, but also in the loss of a carotenoid pigment of unknown function. In this study, we sought to define the mechanism(s) by which cylE may contribute to GBS phagocyte resistance and increased virulence potential. We found that cylE-deficient GBS was more readily cleared from a mouse's bloodstream, human whole blood, and isolated macrophage and neutrophil cultures. Survival was linked to the ability of βH/C to induce cytolysis and apoptosis of the phagocytes. At a lower bacterial inoculum, cylE also contributed to enhanced survival within phagocytes that was attributed to the ability of carotenoid to shield GBS from oxidative damage. In oxidant killing assays, cylE mutants were shown to be more susceptible to hydrogen peroxide, hypochlorite, superoxide, and singlet oxygen. Together, these data suggest a mechanism by which the linked cylE-encoded phenotypes, βH/C (sword) and carotenoid (shield), act in partnership to thwart the immune phagocytic defenses.
National Acad Sciences