Vancomycin for methicillin-resistant staphylococcus aureus biofilm eradication is associated with the emergence of heterogeneous vancomycin intermediate staphylococcus aureus

Vancomycin is the first-line therapy for MRSA infections, even though the standard dose is inadequate for biofilm eradication. This study aimed to asses the efficacy of vancomycin in eradicating biofilms and the influence of exposure on the emergence of hVISA isolates. The biofilm formed by MRSA isolates was exposed to vancomycin concentrations of 1 times the MIC, 1,000 times the MIC, and 10,000 times the MIC; exposed continously for 24 hours vs intermittently for 6 hours/day for 3 days.  Measurement of the optical density of the biofilm was carried out to determine the percentage of biofilm eradication. Biofilm specimens exposed to vancomycin were subcultured onto BHIA-VC selective media to isolate hVISA. The highest biofilm eradication effect was found in isolates exposed to vancomycin at a concentration of 10,000 times the MIC. Vancomycin exposure correlated with the emergence of hVISA isolates, especially after exposure to low concentrations of vancomycin. For optimum eradication of MRSA biofilms, vancomycin concentrations exceeding 1.000 times the MIC are required. Exposure to vancomycin at a dose equal to one-times the MIC had no effect on biofilm eradication and was associated with the emergence of MRSA isolates with decreased susceptibility to vancomycin