Daptomycin Susceptibility of Group B Streptococcus.

We previously reported the emergence and high prevalence of group B streptococci (GBS) with reduced penicillin susceptibility (PRGBS) clinical isolates in Japan. PRGBS tend to be non-susceptible to macrolides and fluoroquinolones. In our previous study, we found that the minimum inhibitory concentration (MIC) of daptomycin for one clinical isolate of GBS was above the susceptible breakpoint settled by the Clinical and Laboratory Standards Institute (CLSI). This suggests the possibility of the unrecognized spread of daptomycin-non-susceptible clinical GBS isolates in Japan. This study aimed to analyze the daptomycin susceptibility in 1,046 clinical GBS isolates that were recovered after the approval of daptomycin in Japan. MICs of daptomycin for the 1,046 clinical isolates were determined by the microdilution method recommended by the CLSI. The MIC range was 0.12-1 µg/mL, and the MIC50 and MIC90 were 0.5 µg/mL and 1 µg/mL, respectively. All the GBS isolates evaluated in this study were susceptible to daptomycin. Therefore, at present, daptomycin might be considered as a new option to treat GBS infections, especially multidrug-resistant PRGBS infections.