Nationwide surveillance of resistance rates of Staphylococcus aureus clinical isolates from Greek hospitals, 2012-2013

Purpose To evaluate the in vitro efficacy of several anti-staphylococcal agents against a nationwide collection of contemporary Staphylococcus aureus clinical isolates from several healthcare centres in Greece. Methods Thirty hospitals throughout Greece (18 in Attica) provided all clinical isolates of S.aureus from April 2012 to May 2013 to a central lab to be re-submitted to susceptibility testing. The MICs were evaluated by Vitek (R) 2 with the exception of ceftaroline (OXOID M.I.C. Evaluator). Vancomycin and daptomycin MICs were also evaluated by Etest (R). Heterogeneously vancomycin-intermediate strains (hVISA) were detected by the Etest (R) GRD. VISA phenotype was confirmed by PAP-AUC. Results A total of 1005 isolates (39% MRSA) were studied. Susceptibility rates were: erythromycin 66.5%, clindamycin 79.2%, SXT 98.9%, rifampicin 97.3%, fusidic acid 67%, moxifloxacin 78.8%, vancomycin 99.9%, ceftaroline 92.9% and linezolid, tigecycline and daptomycin 100%. For mupirocin, high level resistance could be excluded for 98.9% of isolates. Vancomycin Etest (R) MIC50/90 were 1.5/1.5mg/L, 58.5% of isolates exhibited a MIC>1 and 8.7% a MIC of 2mg/L, while Vitek (R) MIC50/90 were 1/1 and 3.1% showed MIC>1mg/L. One VISA strain was detected. Among the selected 175 isolates that were screened for hVISA phenotype, six (3.4%) were positive. In 315 bloodstream isolates, 64.1% had a vancomycin Etest (R) MIC>1mg/L. Conclusions This multi-centre surveillance study revealed that a significant percentage of contemporary S.aureus isolates from Greek patients have a vancomycin MIC (>1mg/L) that may compromise the clinical efficacy of the drug for the treatment of serious infections. The in vitro activity of SXT, rifampicin, mupirocin, linezolid, tigecycline, daptomycin and ceftaroline remains excellent.