Vancomycin not so effective second time round

ink: Microbiological effects of prior vancomycin use in patients with methicillin-resistant Staphylococcus aureus bacteraemia -- Moise et al., 10.1093/jac/dkm445 -- Journal of Antimicrobial Chemotherapy.

Results: Vancomycin MICs were 0.5, 1.0 and 2.0 mg/L for 19, 55 and 7 isolates, respectively. Daptomycin MICs were 0.25, 0.5, 1.0 and 2.0 mg/L for 4, 50, 26 and 1 isolate, respectively. The agr-type distribution was agr group II (59%), group I (25%) and group III (16%); 90% harboured SCCmec II. The genetic background extrapolated by spa-typing showed that 58% of the isolates were of clonal complex 5. MRSA bloodstream isolates from patients who had received vancomycin within the preceding 30 days had a significantly decreased vancomycin killing at 24 h in vitro (median log10 decrease, 3.1 versus 2.2 cfu/mL; P = 0.021) and a significantly higher vancomycin MIC than isolates obtained from patients without that history (P = 0.002). Conclusions: MRSA bloodstream isolates from patients recently treated with vancomycin may demonstrate reduced susceptibility and increased tolerance to vancomycin in vitro. Given that such microbiological phenotypes have been associated with reduced vancomycin efficacy, consideration may be given to alternative Gram-positive antimicrobial therapy in patients who have recently been treated with vancomycin.