Emergence of a strain of methicillin-resistant Staphylococcus aureus with decreased susceptibility to vancomycin 7 months after treatment with glycopeptide antibiotics.

This case report describes a methicillin-resistant Staphylococcus aureus isolated repeatedly from the blood of a patient with community-acquired endocarditis who developed a four-fold increase in the minimal inhibitory concentration of vancomycin and daptomycin 7 months after his last exposure to glycopeptide antibiotics. This is contrary to the expected situation in which antimicrobial resistance tends to decrease after a patient is no longer exposed to vancomycin.