Significance of four methionine sulfoxide reductases in Staphylococcus aureus

Area of Science:

• Microbiology
• Molecular Biology
• Pathogenesis

Background:

• Staphylococcus aureus is a significant human pathogen, with rising antibiotic resistance posing treatment challenges.
• Methionine sulfoxide reductases (Msrs) are induced by cell wall-active antibiotics and combat oxidative stress by reducing methionine sulfoxide.
• S. aureus possesses three msrA genes (msrA1, msrA2, msrA3) and one msrB gene, but their specific roles remain unclear.

Purpose of the Study:

• To elucidate the distinct physiological functions of Msr proteins in S. aureus.
• To investigate the roles of Msr proteins in bacterial growth, antibiotic resistance, adherence, pigment production, and in vivo survival.

Main Methods:

• Site-directed mutagenesis was employed to create single, triple (msrA1, msrA2, msrA3), and quadruple (msrA1, msrA2, msrA3, msrB) mutants of S. aureus.
• Mutant strains were phenotypically characterized for growth, oxidative stress sensitivity, adherence to lung epithelial cells, pigment production, and survival in a mouse model.
• Complementation experiments were performed to confirm the roles of specific Msr proteins.

Main Results:

• MsrA1 deficiency led to increased sensitivity to oxidative stress, reduced pigment production, decreased adherence to lung epithelial cells, and impaired survival in mice.
• MsrB deficiency resulted in enhanced oxidant resistance and increased pigmentation.
• Loss of MsrA2 or MsrA3 did not cause significant growth defects.
• Complementation studies confirmed MsrA1, not MsrB, is critical for adherence and resistance to phagocytosis.

Conclusions:

• MsrA1 functions as a key virulence factor in S. aureus, essential for adherence and resistance to host defenses.
• MsrB appears to play a regulatory role, potentially balancing the effects of MsrA1.
• Targeting MsrA1 could be a potential strategy to combat S. aureus infections.