In vitro activities of aminoglycosides, lincosamides, and rifamycins against Mycobacterium leprae

Abstract

The in vitro activities of a variety of aminoglycosides, lincosamides, and rifamycins against Mycobacterium leprae were evaluated with the BACTEC 460 system. At 20 ,g/ml, gentamicin, kanamycin, tobramycin, streptomycin, and amikacin were inactive. Lincomycin was active at 20 ,ug/ml, and clindamycin was active at 0.31 ,ug/mi. Rifamycin SV, rifabutin, and rifampin were active at 3.1, 3.1 to 12.5, and 200 ng/ml, respectively. The M. leprae inoculum was prepared from infected nude mouse footpads and partially purified by differential centrifugation as previously described (6).All drugs, except for rifabutin (Farmitalia Carlo ERB, Milan, Italy), were obtained from Sigma Chemical Co. (St. Louis, Mo.). Aminoglycosides and lincosamides were dissolved in water, and rifamycins were dissolved in ethanol. All were adjusted for potency, filter sterilized, and diluted in Middlebrook 7H9 broth to 40 times the final desired concentrations.Susceptibility testing was performed with the BACTEC 460 as previously described (3). In brief, i07 M Ieprae organisms were inoculated into BACIEC 12B medium, and drugs were added in 0.1-ml aliquots to quadruplicate vials. All drugs were tested at fourfold dilutions; aminoglycosides and lincosamides were tested at 0.31 to 20 ,ug/ml, and rifamycins were tested at 3.1 to 200 ng/ml. Ampicillin and amphotericin B were added to control occasional contaminants. Vials were flushed with 2.5% 02-10% CO2 (balance, N2) and incubated at 33°C. The growth index (14C02 evolution) was measured at 1-week intervals with the BACTEC 460. Drugs at various concentrations were considered to be active if they effected a significant (Student's t test) reduction in the growth index during the reading interval of days 7 to 14, relative to that of drug-free controls. When these experiments were repeated a second time, essentially identical results were obtained (data not shown).None of the aminoglycosides effected a significant reduction in the growth index at concentrations of 20 ,ug/ml or less after 2 weeks of incubation (Fig. 1). Subsequent readings taken at 3, 4, and 5 weeks postincubation gave similar results (data not shown). In contrast, lincomycin was active at 20 ,ug/ml, and clindamycin was active at 0.31 ,g/ml. At 20 ,ug/ml, clindamycin effected a reduction of 61% in 14CO2evolution.The rifamycins were tested at ¼lo of the concentrations of the aminoglycosides and lincosamides. As previously noted, rifampin was active at 200 ng/ml (Fig. 2). Both rifabutin and rifamycin SV showed significant activity at 3.1 to 200 ng/ml, although the latter effected a greater reduction in the growth index at the lower concentrations.Gelber et al. (10) demonstrated the bactericidal activities of streptomycin, kanamycin, and amikacin at high (100 to 150 mg/kg) daily doses against M. leprae in the footpads of mice. Gentamicin and tobramycin at 20 mg/kg were much less active. Reducing the dose or frequency of administration resulted in a reduction of the activity of streptomycin and a loss of the bactericidal activity of kanamycin (9...

Fusidic acid is highly active against extracellular and intracellular Mycobacterium leprae

“…The present report is the first to use this method to study drug activity against intracellular M. leprae and to study the activity of a single drug both intracellularly and extracellularly. The roughly equal activity of fusidic acid against both intracellu- (6,7,11). Conversely, the Buddemeyer-type detection system is more sensitive (because of the amplification of the signal in the liquid scintillation counting system), and we often find it more useful when working with macrophage-resident (1,19) or biopsy-derived M. leprae.…”

“…We have previously demonstrated the utility of radiorespirometry in evaluating the in vitro activities of a variety of macrolides (9), fluoroquinolones (11), phenazines (10,12), and aminoglycosides, lincosamides, and rifamycins (7) against M. leprae in axenic media with either a Buddemeyertype detection system (5) or the BACTEC 460 instrument (6) as a means of assessing drug activity in the absence of bacterial multiplication. We and our colleagues have also used assays quantitating phenolic glycolipid-1 synthesis and adenosine triphosphate concentration (8) as indices of drug activity against both extracellular (16) and intracellular (20) M. leprae.…”

“…In vitro screening for drugs active against the uncultivable leprosy bacillus can be performed by radiorespirometric analysis of viable Mycobacterium leprae freshly harvested from nude mice (5)(6)(7)(9)(10)(11)(12). In vitro systems have many advantages over the traditional mouse footpad system (22), especially with regard to time, expense, quantity of drug required, and independence of mouse pharmacokinetics.…”

Rifampicin: an inhibitor of Xpl2-specific protein phosphorylation in Xanthomonas oryzae pv. oryzae

“…Rifampicin, a potent inhibitor of DNAdependent RNA polymerase of bacteria, is used extensively as a prokaryotic transcriptional inhibitor. Together with its semisynthetic derivatives, rifampitin is used against mycobacterium infections [5,16], staphylococcus infections [S] and a wide variety of other pathogens. The mechanism of its action is based on the binding of rifampicin to the p subunit of bacterial RNA polymerase which interferes with the formation of the first phosphodiester bond in the Xpl2 infection.…”