Interactions of antibiotics with phagocytes in vitro

The goal of antimicrobial therapy is to eliminate invading bacteria both in the extracellular and intracellular environment. Thus, recent work has focused on the ability of various antibiotics to enter phagocytic cells and kill intracellular pathogens, since bacteria which survive within phagocytes may often produce prolonged or recurrent infections. In the last ten years the antibiotic modulation of phagocytic cell functions has become the subject of our major investigational activity. Taking into account that entry of antibiotics into phagocytes is necessary for activity against intracellular organisms, we examined the uptake of 11 radiolabelled antibiotics by macrophages. Penicillins and cephalosporins were taken up poorly by phagocytes. Teicoplanin was efficiently concentrated by macrophages, achieving intracellular concentrations higher than those in the surrounding extracellular medium. Roxithromycin was more markedly accumulated within phagocytes than was erythromycin, depending upon an active transport mechanism. Antitubercular drugs were concentrated approximately twofold in the macrophages. Besides, since antibiotics that act on phagocytosed bacteria have clinical advantages, we evaluated the direct action of the above mentioned drugs on the macrophage, by determining their interference with its functions or their potentiation of both phagocytosis and killing of bacteria.