Hypersusceptibility of penicillin-treated group B streptococci to bactericidal activity of human polymorphonuclear leukocytes.

Pretreatment of serotype Ib group B streptococci with benzylpenicillin, other beta-lactam antibiotics, or vancomycin increased the susceptibility of these bacteria to the bactericidal activity of a mixture of human polymorphonuclear leukocytes and normal human serum. Increased susceptibility of the bacteria to killing by phagocytes was elicited even by exposure to subinhibitory levels of the beta-lactam antibiotics. Inhibitors of protein synthesis did not induce such susceptibility. We investigated the possible biochemical basis of penicillin-induced susceptibility to phagocytosis. Penicillin treatment induced the release of substantial quantities of group B streptococcal surface components into the growth medium (lipoteichoic acid, lipid, and capsular polysaccharide). Labeling of the live streptococci with 3H-labeled penicillin was used to evaluate the effect of exposure to subinhibitory concentrations of this antibiotic on the penicillin-binding proteins. Our results suggested that beta-lactam antibiotics and components of the immune system may act in concert to eliminate invading bacteria.