The effect of antibiotics on the intracellular survival of bacteria in human phagocytic cells

[14C]-labeled josamycin (Wilprafen) readily enters several types of human phagocytic cells-polymorphonuclear leucocytes (PMNLs), adherent monocytes and alveolar macrophages - and is accumulated by these cells to a concentration about 20 times that in the extracellular medium. Similar studies using [14C]-benzyl penicillin revealed that the beta-lactam antibiotic penetrated these cells very poorly. Low concentrations of josamycin and the various phagocytes acted synergistically to inhibit the intracellular proliferation of L. pneumophila or H. influenzae. In contrast, penicillin G was not effective against legionellae ingested by PMNLs, monocytes or alveolar macrophages, even at high concentrations. The uptake of the antibiotics apparently correlates well with its efficacy against the intracellular survival of bacterial pathogens in human phagocytic cells.