Study of the Synergism Between Carbapenems and Vancomycin or Teicoplanin Against MRSA, Focusing on S-4661, a Carbapenem Newly Developed in Japan

S-4661 is a methylcarbapenem antibiotic newly developed in Japan. We evaluated the combined actions of carbapenems, including S-4661 and vancomycin or teicoplanin, against 27 strains of methicillin-resistant Staphylococcus aureus (MRSA) isolated from the blood of patients admitted to Keio University Hospital, using the checkerboard technique. The minimum inhibitory concentrations (MICs) were determined by the Mueller-Hinton agar method. Most of the strains were highly resistant to carbapenems. Synergy with S-4661, panipenem, meropenem or imipenem, and vancomycin was detected against 92% of the strains tested. Synergy with S-4661, panipenem, meropenem or imipenem, and teicoplanin was detected against 74% of the strains tested. The results of our study suggest that combination therapy of vancomycin or teicoplanin with any of S-4661, panipenem, meropenem, or imipenem would be effective for severe infections due to MRSA strains that are resistant to carbapenems.