Since 1999 the streptogramin combination quinupristin/dalfoprustin and the oxazolidinone linezolid, new classes of synthetic antibacterial agents, exhibit activity against a large number of Gram-positive organisms. Their mode of action has been shown to inhibit protein synthesis. Due to the unique action mechanism of oxazolidinones, it is believed that oxazolidinones do not show cross resistance with other types of antibiotics.