NADase as a target molecule of in vivo suppression of the toxicity in the invasive M-1 group A Streptococcal isolates

The representative high activity isolates taken from STSS patients showed higher virulence compared with isolates from the low activity group, when used to infect mice. The knockout mutant of the nga gene, which encodes NADase also showed reduced virulence in a mouse infection study. The cloned nga gene was able to significantly complement the lost virulence. In addition, the solution containing purified recombinant IFS, which is an inhibitor of NADase, partially rescued mice infected with S. pyogenes.These results indicate that NADase is important for the virulence of S. pyogenes in vivo and is the potential target to suppress the virulence.Group A streptococcus (GAS) is a gram-positive bacterium that infects the upper respiratory tract, including the tonsils and pharynx, and is responsible for post-infectious diseases such as rheumatic fever and glomerulonephritis. In addition, GAS causes severe invasive disease including necrotizing fasciitis [1-6].Although the mechanism of severe invasive disease is still unknown, NAD-glycohydrolase (NADase) secreted by GAS is suspected as one of the virulence factors [7]. NADase has the ability to cleave β-NAD+, which is universally important in numerous essential redox and energy-producing biological reactions, depleting intracellular NAD pools [8,9]. NADase is also toxic for bacterial cells themselves, therefore, GAS encodes ifs gene whose product (IFS) is an endogenous inhibitor of NADase activity and localized in the bacterial cytoplasmic compartment [9,10]. NADase precursor exists as an inactive complex with IFS [9,10]. In vitro, intoxication of keratinocytes with NADase was associated with cytotoxic effects [11,12]. Bricker et al. presented that NADase enhances GAS virulence in vivo using mouse models [13]. These results enabled us to further study the NADase as a target molecule to reduce GAS virulence. However, another study of GAS infection among aboriginal people in Australia found no relationship between NADase produ