S aureus

• Resistance to nafcillin , methicillin andoxacillinis independent of B-lactamase production its under chromosomalcontrol through special gene known as mec A gene.The resistance is related to the lack of certain PBPs in the organisms.• Resistance to vancomycin• Staphylococci are suseptable to vancomycin if the (MIC) is 2 g/mL; ofintermediate susceptibility if the MIC is 4–8 g/mL; and resistant if theMIC is 16 g/mL.• Strains of S aureus with intermediate susceptibility to vancomycin havebeen isolated in Japan. These are often known as vancomycinintermediateS aureus, or "VISA."• They generally have been isolated from patients with complexinfections who have received prolonged vancomycin therapy.• . The mechanism of is associated with increased cell wall synthesis andalterations in the cell wall and is not due to the van genes found inenterococci. resistance