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

Abstract

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.