Lack of a functional methionine sulfoxide reductase (MsrB) increases oxacillin and H₂O₂ stress resistance and enhances pigmentation in Staphylococcus aureus.

Staphylococcus aureus produces 3 MsrA enzymes (MsrA1, MsrA2, and MsrA3) and 1 MsrB enzyme. The genes encoding MsrA1 and MsrB are the first and second genes of a 4-gene operon in S. aureus. In a previous study, MsrA1-deficient S. aureus cells showed increased sensitivity to oxidative stress conditions in spite of a higher production of MsrB. In this study, an msrB mutant of S. aureus was created by site-directed mutagenesis that left the first gene of this locus, msrA1, intact. Studies with this mutant suggest that a deletion of MsrB increases resistance of S. aureus to H2O2 and oxacillin and that the mutant cells produce a higher level of carotenoids relative to wild-type S. aureus cells.