The spread of resistance to antibiotics undermines the therapeutic utility of anti-infective drugs in current clinical use. For example, Staphylococcus aureus, a major cause of community-and hospital-acquired infections, has developed resistance to most classes of antibiotics. Methicillin-resistant S. aureus (MRSA) strains appeared in the hospital environment after introduction of the semisynthetic penicillin methicillin, leaving vancomycin as the last line of defense for MRSA treatment. S. aureus organisms intermediately susceptible to vancomycin were first isolated in 1997 in Japan and later in other countries. With the recent appearance of vancomycin-resistant clinical isolates, no antibiotic class is effective against multiresistant S. aureus infections. The increase in vancomycin-resistant enterococci (VRE), important agents of nosocomial infections, is another cause of great concern. Therapy options for multiresistant gramnegative opportunistic bacterial pathogens are also diminishing. Such bacteria, like Pseudomonas aeruginosa and Burkholderia cepacia, are common environmental organisms and opportunistic pathogens having the capacity to infect essentially all tissues of patients with compromised host defenses