Microbiology of drugs for treating multiply drug-resistant Gram-positive bacteria.

Several new antimicrobials demonstrate in vitro activity against methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant enterococci (VRE), and other Gram-positive bacteria. Data from large surveys indicate that linezolid, daptomycin, and tigecycline are almost universally active against MRSA. Linezolid and tigecycline inhibit both Enterococcus faecium and Enterococcus faecalis at low concentrations; daptomycin is somewhat more potent against the latter. The investigational agents dalbavancin and telavancin are more potent than vancomycin against vancomycin-susceptible organisms. Dalbavancin inhibits vanB type VRE at low concentrations, but is not active against vanA type VRE. Telavancin is less active against VRE than against vancomycin-susceptible enterococci, but minimum inhibitory concentrations are lower than those of vancomycin against VRE. With continued careful use of available antimicrobials, the vast majority of these organisms should remain susceptible to 1 or more of the agents discussed for the foreseeable future.