Enhanced in vitro phagocytosis of Listeria monocytogenes by human monocytes in the presence of ampicillin, tetracycline, and chloramphenicol.

An in vitro system was developed to test the phagocytic activity of human macrophages grown from blood monocytes in the presence of the antibiotics ampicillin, tetracycline, and chloramphenicol. (3)H-labeled Listeria monocytogenes served as test organism. Subinhibitory amounts of the antibiotics enhanced the phagocytic activity significantly (P < 0.025). Macrophages pretreated with the drugs in identical concentrations showed the same phagocytic activity as control cells in the absence of the drugs. Because the drug concentrations used were similar to those that may be attained in man at certain places of inflammation, enhanced phagocytosis in the presence of antibiotics may have clinical significance.