Occurrence and molecular characterization of fusidic acid resistance mechanisms among Staphylococcus spp. from European countries (2008)

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. Isolates displaying a fusidic acid MIC of >= 2 mg/L (non-susceptible; European Committee on Antimicrobial Susceptibility 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 resistance 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. Low S. aureus fusidic acid resistance rates (1%-3%) were observed in Germany, Israel, Italy, Poland, Spain and Sweden. Isolates with MIC values <= 64 mg/L showed a great diversity of acquired fusidic acid resistance mechanisms. Acquired fusidic acid resistance genes were detected in the majority of fusidic acid-resistant isolates from Belgium, France, Switzerland, Sweden, Italy and the UK (72.2%-92.9%), and were slightly less frequent in Germany, Spain and Israel (61.3%-66.7%). Conclusions: This contemporary study showed that acquired fusidic acid resistance genes were prevalent among fusidic acid-non-susceptible European staphylococcal isolates.