Superior in vitro activity of carbapenems over anti-methicillin-resistant Staphylococcus aureus (MRSA) and some related antimicrobial agents for community-acquired MRSA but not for hospital-acquired MRSA

Eighty-eight strains of Panton-Valentine leukocidin (PVL)-positive and -negative community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) and 152 strains of hospital-acquired MRSA (HA-MRSA) were examined for susceptibility to carbapenems, oxacillin, and other antimicrobial agents. CA-MRSA strains were more susceptible to carbapenems (MIC90, 1–4 μg/ml) than HA-MRSA strains (MIC90, 32–64 μg/ml). Among the carbapenems examined, CA-MRSA strains were most susceptible to imipenem (MIC50, 0.12 μg/ml; MIC90, 1 μg/ml). A similar tendency was observed with oxacillin, but less markedly (MIC90: 32 μg/ml for CA-MRSA and ≥256 μg/ml for HA-MRSA). This difference was also observed between CA-MRSA and HA-MRSA in susceptibility levels to cephems, erythromycin, clindamycin, and levofloxacin, but not to ampicillin, vancomycin, teicoplanin, linezolid, and arbekacin. The data indicate that, in terms of MIC50 or MIC90 values, CA-MRSA is 64–256 times more susceptible to imipenem than HA-MRSA, and for CA-MRSA, some carbapenems, e.g., imipenem, show better in vitro activity than anti-MRSA or some related agents.