期刊
JOURNAL OF CLINICAL INVESTIGATION
卷 111, 期 1, 页码 61-70出版社
AMER SOC CLINICAL INVESTIGATION INC
DOI: 10.1172/JCI200316270
关键词
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资金
- NIAID NIH HHS [5 F32 AI10426-03, N01AI30068, F32 AI010426, R01AI 40918] Funding Source: Medline
- NATIONAL INSTITUTE OF ALLERGY AND INFECTIOUS DISEASES [F32AI010426, R01AI040918] Funding Source: NIH RePORTER
Group B streptococcus (GBS) is an important human pathogen. In this study, we sought to identify mechanisms that may protect GBS from host defenses in addition to its capsular polysaccharide. A gene encoding a cell-surface-associated protein (cspA) was characterized from a highly virulent type III GBS isolate, COH1. Its sequence indicated that it is a subtilisin-like extracellular serine protease homologous to streptococcal C5a peptidases and caseinases of lactic acid bacteria. The wild-type strain cleaved the a chain of human fibrinogen, whereas a cspA mutant, TOH121, was unable to cleave fibrinogen. We observed aggregated material when COH1 was incubated with fibrinogen but not when the mutant strain was treated similarly. This suggested that the product(s) of fibrinogen cleavage have strong adhesive properties and may be similar to fibrin. The cspA gene was present among representative clinical isolates from all nine capsular serotypes, as revealed by Southern blotting. A cspA(-) mutant was ten times less virulent in a neonatal rat sepsis model of GBS infections, as measured by LD50 analysis. In addition, the cspA- mutant was significantly more sensitive than the wildtype strain to opsonophagocytic killing by human neutrophils in vitro. Taken together, the results suggest that cleavage of fibrinogen by CspA may increase the lethality of GBS infection, potentially by protecting the bacterium from opsonophagocytic killing.
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