Sword and shield: linked group B streptococcal beta-hemolysin/cytolysin and carotenoid pigment function to subvert host phagocyte defense.
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 beta-hemolysin/cytolysin (betaH/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 betaH/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 betaH/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, betaH/C (sword) and carotenoid (shield), act in partnership to thwart the immune phagocytic defenses.
Liu
George Y
GY
Department of Pediatrics, The Scripps Institution of Oceanography, University of California at San Diego, La Jolla, CA 92093, USA.
Doran
Kelly S
KS
Lawrence
Toby
T
Turkson
Nicole
N
Puliti
Manuela
M
Tissi
Luciana
L
Nizet
Victor
V
D000818:Animals; D017209:Apoptosis; D001426:Bacterial Proteins; D001483:Base Sequence; D002338:Carotenoids / Q000235:genetics / Q000633:toxicity*; D002460:Cell Line; D003603:Cytotoxins / Q000235:genetics / Q000633:toxicity*; D004269:DNA, Bacterial / Q000235:genetics; D005798:Genes, Bacterial; D006460:Hemolysin Proteins / Q000235:genetics / Q000633:toxicity*; D006801:Humans; D051379:Mice; D009154:Mutation; D010586:Phagocytes / Q000187:drug effects* / Q000276:immunology* / Q000473:pathology; D017382:Reactive Oxygen Species / Q000378:metabolism; D018805:Sepsis / Q000276:immunology / Q000473:pathology; D013290:Streptococcal Infections / Q000276:immunology / Q000473:pathology; D013292:Streptococcus agalactiae / Q000235:genetics / Q000472:pathogenicity*; D014774:Virulence / Q000235:genetics / Q000502:physiology
D001426:Bacterial Proteins; D003603:Cytotoxins; D004269:DNA, Bacterial; D006460:Hemolysin Proteins; D017382:Reactive Oxygen Species; C071495:streptococcal group B hemolysin; D002338:Carotenoids