Influence of subinhibitory concentrations of penicillin, cephalothin, and clindamycin on Staphylococcus aureus growth in human phagocytic cells

After an initial 2-h incubation with phagocytic cells, the growth of surviving intracellular Staphylococcus aureus was examined in the presence of subinhibitory concentrations of penicillin, cephalothin, and clindamycin. One-tenth of the minimal inhibitory concentrations of these antibiotics markedly reduced bacterial growth in normal polymorphonuclear leukocytes. In contrast, when human alveolar macrophages were studied, no inhibition of growth was seen. Subinhibitory concentrations of these antibiotics and polymorphonuclear leukocytes acted synergistically to reduce intracellular survival of S. aureus. This synergy did not appear to be dependent upon the microbicidal potential of the leukocyte respiratory burst, since no differences were found when polymorphonuclear leukocytes obtained from patients with chronic granulomatous disease were compared with those from normal donors.