Efficacies of quinupristin-dalfopristin combined with vancomycin in vitro and in experimental endocarditis due to methicillin-resistant staphylococcus aureus in relation to cross-resistance to macrolides, lincosamides, and streptogramin B-type antibiotics

A beneficial effect of the combination of quinupristin-dalfopristin and vancomycin was observed against two methicillin-resistant strains of Staphylococcus aureus harboring or not harboring the ermC gene, which codes for constitutive macrolide, lincosamide, and streptogramin B resistance. The beneficial effect was observed in time-kill studies, in which the drugs were used at inhibitory concentrations, and in a rabbit model of endocarditis, in which the combination was highly bactericidal and more active than monotherapies.