SPX and abscess: For instance, sigB gene-deficient mutant was found to be less virulent in mouse models of arthritis [48] and intraperitoneal infection [49]; whereas mouse model of the abscess and hematogenous pyelonephritis [50], and a rat model of osteomyelitis [51] found no role of SigB in virulence of S. aureus. Similarly, the absence of SigB causes reduced pigmentation irrespective of the presence of YjbH or Spx, and the absence of Spx was required for the enhanced proteolytic activity of sigB-yjbH double gene disruptant [20].