Reduced susceptibility to quinupristin/dalfopristin in Enterococcus faecium in Greece without prior exposure to the agent

During 2005-2006, a total of 865 Enterococcus faecium isolated from patients from eight Greek hospitals were tested for susceptibility to quinupristin/dalfopristin (Q/D). Among them, 250 genetically unrelated strains (28.9%) were found to be intermediate-resistant to Q/D (minimum inhibitory concentration (MIC) 1.5-4 mg/L); all were resistant to dalfopristin (MIC = 16-64 mg/L), whilst 69% were resistant to quinupristin, carrying the ermB gene. No strain was found to carry any of the known genes, such as vatE and vatD, involved in Q/D resistance, indicating that a non-transferable undetermined mechanism is responsible for the expression of low-level Q/D resistance. The high percentage of Q/D-intermediate-resistant E. faecium in Greece was not associated with prior consumption of the agent or with the veterinary use of virginiamycin. (C) 2007 Elsevier B.V. and the International Society of Chemotherapy. All rights reserved