4.2. Antimicrobial Susceptibility Testing

For all the isolates, minimal inhibitory concentrations (MICs) within limited ranges were measured by the broth microdilution test using Dry Plate Eiken DP32 (Eiken, Tokyo, Japan) for 18 antimicrobials: oxacillin (OXA), ampicillin (AMP), cefazolin (CFZ), cefmetazole (CMZ), flomoxef (FMX), imipenem (IPM), gentamicin (GEN), arbekacin (ABK), erythromycin (ERY), clindamycin (CLI), vancomycin (VAN), teicoplanin (TEC), linezolid (LZD), minocycline (MIN), fosfomycin (FOF), levofloxacin (LVX), cefoxitin (FOX) and trimethoprim/sulfamethoxazole (SXT). Inducible clindamycin resistance (CLI-i) was determined by the D-zone test. Resistance was judged according to break points mentioned in the Clinical Laboratory Standards Institute (CLSI) standards [53] for most of the antimicrobials tested. For antimicrobial drugs whose breakpoints are not available in CLSI standards, we employed the European Committee on Antimicrobial Susceptibility Testing (EUCAST) breakpoint for FOF (32 mg/L, Staphylococcus spp.) [54], and a unique breakpoint for ABK (4 mg/L which is higher than the 2 mg/L, defined by the Japanese Society of Chemotherapy for respiratory infection), and a breakpoint of FMX (16 mg/L) defined by the Japanese Society of Chemotherapy for urinary tract infection [55].