An in vitro investigation of the intracellular bioactivity of amoxicillin, clindamycin, and erythromycin for Staphylococcus aureus.

The intraphagocytic bioactivities for Staphylococcus aureus of amoxicillin, clindamycin, and erythromycin (0.0075-20 micrograms/ml) were measured in human polymorphonuclear leukocytes (PMNLs) with the combination of a fluorochrome microassay and a radioassay. PMNLs with normal or depleted membrane-associated oxidative metabolism were used to investigate the interactions that may occur between the intrinsic O2-dependent antimicrobial systems of human phagocytes and antimicrobial agents in the elimination of intracellular microbial pathogens. Neutralization of O2-dependent antimicrobial systems with retention of phagocytic capacity was achieved with use of PMNLs from four children with chronic granulomatous disease (CGD) or NaF-pulsed normal PMNLs. None of the test antibiotics possessed intracellular bactericidal activity. Clindamycin and erythromycin possessed significant intracellular bacteriostatic activity relative to the modest activity of amoxicillin. Optimal intracellular bioactivity of all three antibiotics was obtained with normal PMNLs relative to NaF-pulsed or CGD PMNLs, a result indicating the existence of beneficial interactions between the antimicrobial agents and the O2-dependent antimicrobial systems of PMNLs.