Antibiotic resistance, population structure and spread of Staphylococcus aureus in nursing homes in the Euregion Meuse-Rhine

To determine the spread of Staphylococcus aureus within and between nursing home (NH) residents in the Euregion Meuse-Rhine, a cross-border region of the Netherlands and Germany, we investigated the prevalence of antibiotic resistance, genetic background and population structure of both methicillin-susceptible S. aureus (MSSA) and methicillin-resistant S. aureus (MRSA) isolates. A total of 245 S. aureus isolates were collected from NH residents. Susceptibility testing was performed with microbroth dilution. The genetic background was determined using spa typing, SCCmec typing, pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST). Differences in the prevalence of resistance between the German and Dutch MSSA isolates were observed for the macrolides (15 % vs. 2 %, p = 0.003), clindamycin (15 % vs. 0 %, p = 0.003) and ciprofloxacin (34 % vs. 25 %). The macrolide and ciprofloxacin resistance varied between the NHs, while trimethoprim-sulfamethoxazole resistance was low in all residents. The MRSA prevalence was 3.5 % and <1 % among the German and Dutch NH residents, respectively (p = 0.005). The German MRSAs, isolated in 7 out of 10 NHs, belonged to ST22-MRSA-IV or ST225-MRSA-II. spa clonal complexes (spa-CCs) 015 and 002 were prevalent among the German MSSA isolates and spa-CCs 024 and 1716 were prevalent among the Dutch MSSA isolates. The antibiotic resistance of MSSA and the MRSA prevalence were significantly higher among the German NH residents. The spread of two MRSA clones was observed within and between the German NHs, but not between the Dutch and German NHs. Differences in the prevalence of resistance and the prevalence of MRSA between NHs on both sides of the border warrant the continuation of surveillance at a local level.