Group B streptococci inhibit the chemotactic activity of the fifth component of complement.

Infection with group B streptococci (GBS) is associated with a poor acute inflammatory response in which neutrophils fail to localize at the site of invasion. In the present studies, we have examined the effects of group B streptococci on C-derived chemotactic activity in human serum. Fresh human serum was activated to form C5a and C5adesarg by incubation with zymosan. The activated serum was then incubated with group B organisms, centrifuged, and the supernatants tested for chemotactic activity for human polymorphonuclear leukocytes. Group B organisms caused a dose-dependent decrease in C-dependent chemotactic activity. The degree of inhibition was profound with 1 X 10(9) bacteria/ml (10% of control). Experiments indicated that significant chemotactic factor inactivation occurred within 2 min of exposure to GBS organisms, while maximal inhibition occurred after 30 min incubation. A number of different strains of GBS of types I, II, and III possessed inhibitory activity. In contrast, group D streptococci, Staphylococcus aureus, Escherichia coli and Klebsiella pneumoniae failed to inhibit the C-derived chemotactic activity in human serum. Group A streptococci that were M protein positive also inactivated C-dependent chemotactic activity in serum, as previously reported. The inhibitory activity of the GBS strains could be abolished by heat or trypsin treatment but not by neuraminidase, pronase, or pepsin. C5a levels in zymosan-activated serum as measured by RIA were not decreased after incubation with an inhibitory strain suggesting that absorption was not involved. SDS-PAGE analysis revealed that group B streptococci degrade the C5a molecule, increasing its electrophoretic mobility by removing a fragment with a m.w. of approximately 650 Da. Thus, one of the reasons for the poor inflammatory response at the site of GBS infection may reside in the ability of these pathogens to inactivate C-derived inflammatory mediators. The GBS C5a-ase activity probably serves as an additional virulence factor for these organisms contributing to the poor inflammatory response characteristic of group B streptococcal infection.