Enhancement of opsonophagocytosis of Bacteroides spp. by clindamycin in subinhibitory concentrations.

Radioactively labelled bacteria were incubated overnight in the presence or absence of one-half the MIC of clindamycin, then preopsonized with normal human serum or homologous rabbit antiserum and incubated with human polymorphonuclear leucocytes. Clindamycin in subinhibitory concentrations significantly enhanced the phagocytosis of all four Bacteroides strains. Complement-dependent as well as antibody-dependent phagocytosis was enhanced by clindamycin in one Bacteroides strain. In the other three strains, only antibody dependent phagocytosis was enhanced by clindamycin. Transmission electron microscopy confirmed phagocytosis of the bacteroides.