| Abstract: | In vitro drug effects on Mycobacterium leprae (M. leprae) in a cell-free system have been monitored by mass spectrometric determination of the ratio of the intrabacterial concentrations of the sodium and potassium ions (Na+, K+ ratio) of a limited number of individual bacteria per sample. From the drug-induced increase of the median values of the distributions of the Na+, K+ ratio, information on the concentration and time dependence of drug effects as well as on antagonistic or synergistic interactions of drugs has been obtained. Moreover, absolute values for the percentage of killed bacteria (% kill) have been derived from the distribution of the Na+, K+ ratios within a bacterial population. For this, the limiting value of the Na+, K+ ratio (up to which bacteria are viable) —which had been determined as 0.45 for cultivable bacteria — has been presumed to be valid also for M. leprae. Highest killing rates have been observed for fusidic acid and clarithromycin, followed by rifabutine, rifampin, and clofazimine. Minocycline and dapsone have shown only moderate killing effects and isoniazid and — probably due to the restricted metabolism of M. leprae in a cell-free medium — ofloxacin have been completely inactive. Strong ofloxacin effects, however, have been observed for cultivable mycobacteria and intracellular M. leprae phagocytized by a murine macrophage cell line. |
