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The chelating antibiotic nitroxoline (5-nitro-8-hydroxyquinoline) showed a bacteriostatic effect at a concentration of 10 microM for Mycobacterium bovis BCG. At higher concentrations the compound showed moderate cidal activity against growing bacilli. In contrast, its non-nitrated derivative oxine (8-hydroxyquinoline, MIC=2 microM) reduced the viability of a growing culture rapidly, 5000-fold at a concentration where the nitroxoline was merely bacteriostatic. Both compounds showed appreciable cidal activity against bacilli in their hypoxic dormant state.

Depletion of oxygen triggers the shift-down of Mycobacterium bovis BCG to a state of dormancy. Bacilli in their dormant state are resistant to standard anti-mycobacterials. The nitroimidazole metronidazole was the first compound identified to show bactericidal activity against dormant tubercle bacilli. In contrast to metronidazole's selective toxicity for dormant bacilli, we report here that the nitrofurans nitrofurantoin, furaltadone and nitrofurazone showed bactericidal activity against dormant and growing bacteria. Importantly, the bactericidal effect of nitrofurans on dormant bacilli was 35- to 250-fold higher compared with metronidazole.