Seeking vancomycin resistant Staphylococcus aureus among patients with vancomycin-resistant enterococci

Clinical isolates of Staphylococcus aureus displaying intermediate resistan ce to vancomycin (VISA) have been identified. The objective of our study wa s to identify VISA colonization among patients known to be colonized or inf ected with vancomycin-resistant: enterococci (VRE). Eight weekly point prev alence screening surveys for VRE and S. aureus were conducted on 5 hospital units. Of the 243 patients screened, 31 (12.8%) were colonized with VRE. I n addition, 18 inpatients were already known to be VRE-positive. Fourteen ( 28.6%) of the 49 VRE-positive patients were co-colonized with S. aureus. Al l 30 S. aureus isolates from these 14 patients were methicillin-resistant ( MRSA) but remained vancomycin-susceptible (minimal inhibitory concentration [MIC] range, 0.75-2 mu g/mL). Population analysis profiling demonstrated n o evidence of heteroresistant subpopulations that could grow on agar contai ning 3 mu g/mL, vancomycin for any of the MRSA isolates. Although 23 (77%) of 30 staphylococcal isolates had vancomycin MICs of 1.5 or 2 mu g/mL, no V ISA strains (MICs, 8-16 mu g/mL) were recovered.