Under different conditions, for example longer incubation times and anaerobic conditions, nitrite production has been found in some BCG strains

(Weber et al., 2000; Sohaskey & Wayne, 2003; Stermann et al., 2003; Sohaskey & Modesti, 2009). Therefore, different incubation times could explain the discrepancy observed between nitrate reductase test results and intercellular survival. Nitrate reductase activity is not the sole explanation, but we believe it is partly responsible for the survival in host cells, as shown in previous reports (Weber et al., 2000; Sohaskey, 2008) and the present study. Heterogeneity of niacin accumulation was also observed among BCG substrains (Table 1). Recycling of NAD favours the latent infection of M. tuberculosis (Boshoff et al., 2008), and NAD-quinoline reductase is responsible for resistance

to oxidative stress (Akhtar et al., 2006). These reports suggest that the BTK assay find more activity of NAD metabolism is associated with the survival of BCG in macrophages or host cells. Whether the long or short survival of BCG in host cells favours the effectiveness of BCG has not been determined. However, the different characteristics of BCG substrains as reported here provide the basic information for further investigation of immunological characteristics and evaluation. Parker et al. (2007) purified and characterized MPLA. MPLA is associated with cutinase, a serine esterase and catalyses the hydrolysis of lipids including Tween 80. MPLA activity was observed not only in pathogenic M. tuberculosis, but also in BCG-Pasteur. BCG-Pasteur

was weakly positive for Tween 80 hydrolysis (Table 1). In fact, eight of the 14 substrains, namely BCG-Moreau, -Sweden, -Danish, -Connaught, -Montreal, -Phipps, -Australia and -Pasteur, were weakly positive. Mycobacteria are known to use this fatty acid as carbon source at the dormant stage. Therefore, this activity could contribute to survival under starvation conditions during dormancy (Jackson et al., 1989; Deb et al., 17-DMAG (Alvespimycin) HCl 2009). All BCG strains belong to the low-catalase group, although there were variations in the height of bubble column among them (Table 1). It was over 10 mm in BCG-Japan (14.8 mm) and -Birkhaug (11.8 mm) (Table 1). No mutation in the coding region of the ahpC gene among was observed among the substrains (data not shown). The differences between transcription of the genes and the activities have not yet been analysed. Catalase (katG) and peroxidase (ahpC) activities of M. tuberculosis are related to resistance to oxidative killing in human monocytes in vitro (Manca et al., 1999). The expression of katG is partially regulated by ferric uptake regulators (fur), and contributes to the virulence of M. tuberculosis (Lucarelli et al., 2008). Resistance to hydrogen peroxide of M. bovis, BCG-Russia and -Japan was higher than that of other BCG substrains (Fig. 1). This resistance relates well to survival in host cells, THP-1 and BMMs (Fig. 1).