Influence of culture medium on the resistance and response of Mycobacterium bovis BCG to reactive nitrogen intermediates

The aim of the present work was to evaluate the influence of the culture medium on the resistance and response of Mycobacterium bovis BCG to reactive nitrogen intermediates, in vitro. BCG was grown in Sauton, Dubos or Middlebrook 7H9 medium and exposed to sodium nitroprusside (SNP) for up to 7 days. The percentage of bacilli that survived was significantly lower in Middlebrook 7H9 than in Sauton or Dubos medium. Addition of SNP to Middlebrook 7H9 caused an increase in the RedOx potential in either the absence or the presence of BCG, while addition of the compound to Sauton medium gave rise to an increase in the RedOx potential only in the absence of bacteria, whereas a decrease in the RedOx potential was observed in the presence of BCG. The resistance of BCG to SNP in the different media did not correlate with the concentration of peroxynitrite in culture supernatants. BCG grown in different media showed a differential protein expression pattern, as assessed by two-dimensional gel electrophoresis. Exposure of BCG to sub-lethal concentrations of SNP in Middlebrook 7H9, but not in Sauton medium, revealed a differential expression of at least 38 protein species. Altogether these results demonstrate that the growth medium may have a remarkable influence on the resistance and the response of BCG to SNP and suggest that the different resistance of BCG in the two media is unlikely to be due to a differential antioxidant effect of the medium itself.