Influence of a Sub—inhibitory Concentration of Antibiotics on Opsono-phagocytic Functions of Klebsiella Pneumoniae by Human Phagocytes

Klebsiella pneumoniae 163 was grown in the presence of 1/4 MIC of cefodizime (CDZM) or cefpimizole (CPIZ) for 3 hours. The killing rate of drug-treated bacteria by human polymorphonuclear leukocytes (PMNs) was significantly enhanced, compared with that of the untreated bacteria (p<0.01). Study of opsonization kinetics by a chemiluminescence assay demonstrated that drug-treated bacteria were opsonized more rapidly than control bacteria (p<0.01), and serum complement was consumed much faster when Klebsiella pneumoniae was preincubated with each drug (P<0.01). Furthermore, Klebsiella pneumoniae treated with 1/4 MIC of CDZM or CPIZ was more sensitive to hydrogen peroxide (H2O2), one of the oxygen-free radicals produced by phagocytes (P<0.01). These results show that Klebsiella pneumoniae treated by 1/4 MIC of CDZM or CPIZ is much more susceptible to the bactericidal activity of human PMNs than untreated controls. This potentiation of host defense by sub-MICs of antibiotics might be a favorable consequence in patients treated with these drugs for infections caused by Klebsiella pneumoniae.