Occurrence and molecular characterization of fusidic acid resistance mechanisms among Staphylococcus spp. from European countries

Objectives: To determine fusidic acid resistance rates (MICs of ≥2 mg/L) and the prevalence of fusidic acid resistance mechanisms among Staphylococcus spp. collected from European countries (2008). Methods: Staphylococcal isolates (3134) collected from Europe were tested by CLSI broth microdilution. Iso-lates displaying a fusidic acid MIC of ≥2 mg/L (non-susceptible; European Committee on Antimicrobial Suscep-tibility Testing breakpoint) were tested for fusB, fusC and fusD. The fusidic acid target sites fusA and fusE were then sequenced, and a method for the detection of the fusA mutation L461K was developed. Selected isolates were typed by PFGE. Results: Fusidic acid resistance rates were higher among coagulase-negative staphylococci (CoNS) compared with Staphylococcus aureus. Acquired fusidic acid resistance genes were detected in 64.9 % of the samples; fusB and fusC were detected among 10.1 % and 16.9 % of the fusidic acid-resistant S. aureus and among 26.5 % and 11.3 % of the CoNS, respectively. Ireland and Greece showed the highest S. aureus fusidic acid resist-ance levels, with low rates of acquired fusidic acid resistance genes. Isolates from these countries displayed MIC values of ≥512 mg/L, the presence of the elongation factor G L461K alteration and clonal occurrences. Lo