SYNERGISTIC EFFECT OF AZITHROMYCIN ON THE PHAGOCYTIC KILLING OF STAPHYLOCOCCUS-AUREUS BY HUMAN POLYMORPHONUCLEAR LEUKOCYTES

Many macrolides have been shown to affect the interaction between bact eria and various immune defense mechanisms, such as chemotaxis, accumu lation, and bioactivity within phagocytic cells. The interaction of az ithromycin with human polymorphonuclear leukocytes (PMNs) was studied in vitro and compared with the interactions between other macrolides a nd PMNs. The opsonophagocytic killing of Staphylococcus aureus was syn ergistically enhanced by azithromycin at concentrations below and abov e the minimal inhibitory concentration, with a reduction of up to 2.82 log(10) cfu/ml with 2 mg/ml of azithromycin. Other macrolides were ef fective only at subinhibitory concentrations. The beneficial azithromy cin-leukocyte interaction may explain azithromycin's efficacy against intracellular pathogens.