Antimicrobial susceptibility testing was performed using the broth microdilution assay as described by Deutsches Institut für Normung, DIN 58940. [19] Interpretation of the results was done according to the EUCAST standard [20] . The MIC test panel included penicillin G, oxacillin, gentamicin, erythromycin, clindamycin, ciprofloxacin, moxifloxacin, oxytetracycline, cotrimoxazol, rifampicin, fusidic acid, fosfomycin, linezolid, mupirocin, daptomycin, tigecyclin, vancomycin, and teicoplanin. Furthermore all isolates were checked for susceptibility against oxacillin/sulbactam by a tube test as described previously [21] (link).
Test for growth on chromogenic selective agar plates: Colonies grown on blood agar plates after overnight incubation were suspended in 0.9% NaCl solution with a turbidity corresponding to the 0.5 McFarland turbidity standard. This suspension and appropriate dilutions were inoculated in parallel onto sheep blood agar plates (Mueller Hinton agar containing sheep blood, OXOID) and onto chromogenic agar plates from three different manufacturers (chromID™ MRSA, bioMerieux; Brilliance™ MRSA, Oxoid; chromagar™ MRSA, Becton Dickinson). Growth was recorded after overnight incubation at 37±1°C. Efficiency of plating was calculated as the proportion of colony forming units on selective agar plates in comparison to blood agar plates.
Phenotypic test for the expression of PBP2a: The Slidex Staph MRSA test kit from bioMerieux was used as recommended by the manufacturer.
Test for growth on chromogenic selective agar plates: Colonies grown on blood agar plates after overnight incubation were suspended in 0.9% NaCl solution with a turbidity corresponding to the 0.5 McFarland turbidity standard. This suspension and appropriate dilutions were inoculated in parallel onto sheep blood agar plates (Mueller Hinton agar containing sheep blood, OXOID) and onto chromogenic agar plates from three different manufacturers (chromID™ MRSA, bioMerieux; Brilliance™ MRSA, Oxoid; chromagar™ MRSA, Becton Dickinson). Growth was recorded after overnight incubation at 37±1°C. Efficiency of plating was calculated as the proportion of colony forming units on selective agar plates in comparison to blood agar plates.
Phenotypic test for the expression of PBP2a: The Slidex Staph MRSA test kit from bioMerieux was used as recommended by the manufacturer.