These reports created our interest in NADase as a target molecule to reduce the GAS virulence. However, before studying the ability of a NADase-inhibitor to reduce GAS virulence, we felt NADase itself should be further characterized in its virulence selleck chemical causing role based on the following two reasons. (i) In M type-3 clinical isolate used in the previous study, the difference between mortality of mice infected with the nga strain and the parental

strain was about only 25% [13]. Meanwhile, we recently reported that M-1 group A streptococcal isolates are divided into three groups based on NADase activity: high activity, low activity and no activity [15]. If a high-activity isolate is used to measure mortality of mice infected with GAS compared with the nga strain, the difference could be wider than if a low activity isolate were used. Indeed,

in this study, we found that the difference between mortalities of mice infected with GT01 (12/15 = 80% death), a high-activity isolate, and the GT01Δnga (0/8 = 0% death) was 80% (see Table 2). In addition, the difference in mice mortality between the cases of GT01 (pLZ12-Km2, vector plasmid) and GT01Δnga (pLZ12-Km2) was 73% (see Table 3). This result shows that the GT01 isolate could provide an advantage compared with the M type-3 clinical isolate when studying the ability of a NADase-inhibitor to reduce GAS virulence, which is our original interest. (ii) To our knowledge, the reduced virulence of the nga-deletion selleck kinase inhibitor mutant of GAS has never been successfully complemented using a cloned nga gene. It is common knowledge that complementation tests in vivo are not easily accomplished due to increased technical Urocanase problems when compared to an in vitro study. In such cases, some alternative methods can be used. For example, Bricker et al. [13] constructed

two independent nga-deficient mutants and showed that they have similar phenotypes. In this study, we added two more points of supportive data. We showed that an nga knockout GAS strain possessing a cloned nga gene partially restored virulence (Figure 2 and Table 3). In addition, we showed that a solution containing purified IFS suppressed the virulence of GAS in the experimental mouse-infection model (see later for additional discussion). Although the data of Table 2 support our conclusion described earlier, some of the individual data were inconsistent with each other. For example, some of the strains belonging to low- and high-activity groups showed similar survival curves. However, this is not surprising because multiple factors play a role in GAS virulence, and the productions of virulent factors differ among the strains [25]. Therefore, it is important to compare groups including multiple, but not single, strains.