[Antibacterial activity of clindamycin and lincomycin in broth, serum, and in combination with polymorphonuclear...

We investigated the antibacterial activity of clindamycin and lincomycin at 1/4 X minimum inhibitory concentration (MIC), 1 X MIC and 4 X MIC against a serum-resistant Staphylococcus aureus and a serum-resistant Staphylococcus epidermidis strain in broth, in serum with and without the presence of leukocytes and in Hank's medium in combination with leukocytes alone. Against both test strains, lincomycin in broth and serum was similarly effective, whereas against S. aureus clindamycin in broth was somewhat more active. In the combined test mixture of serum with leukocytes, even a 1/4 X MIC of clindamycin or lincomycin markedly improved leukocyte killing of S. aureus, whereas both compounds could not further enhance the marked leukocyte killing of S. epidermidis, even at inhibitory concentrations. In Hank's medium with leukocytes alone, clindamycin and lincomycin had at the most only a bacteriostatic effect against both test strains.