Comparative Study of the Difference in Behavior of the Accessory Gene Regulator (Agr) in USA300 and USA400 Community- Associated Methicillin-Resistant Staphylococcus aureus (CA-MRSA)

Community-associated Methicillin-Resistant Staphylococcus aureus (CA-MRSA) is notorious as a leading cause of soft tissue infections. Despite several studies on the Agr regulator, the mechanisms of action of Agr on the virulence factors in different strains are still unknown. To reveal the role of Agr in different CA-MRSA, we investigated the LAC Delta agr mutant and the MW2 Delta agr mutant by comparing LAC (USA300), MW2 (USA400), and Delta agr mutants. The changes of Delta agr mutants in sensitivity to oxacillin and several virulence factors such as biofilm formation, pigmentation, motility, and membrane properties were monitored. LAC Delta agr and MW2 Delta agr mutants showed different oxacillin sensitivity and biofilm formation compared to the LAC and MW2 strains. Regardless of the strain, the motility was reduced in Delta agr mutants. And there was an increase in the long chain fatty acid in phospholipid fatty acid composition of Delta agr mutants. Other properties such as biofilm formation, pigmentation, motility, and membrane properties were different in both Delta agr mutants. The Agr regulator may have a common role like the control of motility and strain dependent roles such as antibiotic resistance, biofilm formation, change of membrane, and pigment production. It does not seem easy to control all MRSA by targeting the Agr regulator only as it showed strain-dependent behaviors.