ERYTHROMYCIN IS INEFFECTIVE AGAINST LISTERIA-MONOCYTOGENES IN MULTIDRUG-RESISTANT CELLS

Multidrug resistance of tumor cells is a well-known phenomenon in onco logy. Among the substances excluded from the cells are not only antine oplastic drugs but also certain antibiotics, e.g. erythromycin. To pro ve the hypothesis that this might render infections with intracellular bacteria untreatable with these antibiotics we used erythromycin to t reat intracellular infection of multidrug resistant (MDR) cells with L isteria monocytogenes. Erythromycin was unable to restrict the growth of L. monocytogenes in KBV-1 MDR cells in concentrations of up to 25 m u g/ml. In contrast, 0.049 mu g/ml of erythromycin were sufficient to restrict the growth of the bacteria in nonresistant KB 3-1 cells. When verapamil was added to the supernatant of KBV-1 cells, erythromycin r egained its effectivity on L. monocytogenes multiplying in these cells . The fact that MDR cells may render intracellular bacteria inaccessib le to certain antibiotics might have important implications for the pe rsistence of these bacteria in the host and for the treatment of patie nts with genetically engineered MDR cells.