MAS1 and osteomyelitis: Thus, the reason(s) mutation of mgrA and rot limit the virulence of UAMS-1 in osteomyelitis remain to be determined, but, irrespective of the mechanism(s) involved, these results do not contradict the conclusion that sarA is the only regulatory locus among those we examined that is consistently associated with reduced virulence in diverse clinical isolates of S. aureus.