Activity of linezolid against Gram-positive cocci possessing genes conferring resistance to protein synthesis inhibitors

Linezolid belongs to a new class of antimicrobials, the oxazolidinones, that act by inhibiting protein synthesis. To detect cross-resistance with other inhibitors of protein synthesis (chloramphenicol, macrolides, lincosamides, streptogramins, aminoglycosides and tetracyclines), the in vitro activity of linezolid was determined against isolates harbouring known genes conferring resistance to these antimicrobials. Neither the presence of modifying enzymes (LinA, LinA', LinB, Vgb, Vat, SatA, ANT(4') (4")-I, AAC(6')-APH(2"), APHA-3 and Cat), nor the presence of an efflux mechanism (MsrA, MefE, MefA, MreA, Vga, TetK and TeL), nor the modification or protection of antimicrobial target (because of ribosomal methylases or TetM and TetO) affected linezolid activity as demonstrated by similar in vitro activity against resistant isolates and sensitive control isolates.