Although all clinical isolates of group B Streptococcus (GBS; Streptococcus agalactiae) have been considered susceptible to beta-lactams including penicillins, we reported the existence of GBS with reduced penicillin susceptibility (PRGBS), which harbors amino acid substitutions in penicillin-binding proteins (PBPs), at the Interscience Conference on Antimicrobial Agents and Chemotherapy in 2006 and in Antimicrobial Agents and Chemotherapy in 2008 (K. Kimura et al. Antimicrob Agents Chemother 2008: 52(8): 2890–2897). In 2014, we reported on clinical isolates of penicillin-susceptible GBS with reduced cephalosporin susceptibility (N. Nagano et al. J Clin Microbiol 2014: 52(9): 3406–3410) and proposed a classification of GBS with reduced beta-lactam susceptibility (GBS-RBS) based on the amino acid substitutions in the PBPs (K. Kimura, N. Nagano, Y. Arakawa. J Antimicrob Chemother 2015: 70(6): 1601–1603). PRGBS tends to be nonsusceptible to both macrolides and fluoroquinolones, in addition to penicillins and some cephalosporins (K. Kimura et al. J Antimicrob Chemother 2013: 68(3): 539–542). The isolation rate of such multidrug-resistant PRGBS was 10.1% (31/306) during 2012–2013 in Japan (T. Seki et al. J Antimicrob Chemother 2015: 70(10): 2725–2728). We also reported the minimum inhibitory concentrations of 22 antibacterial drugs and compounds for 74 PRGBS isolates (M. Kitamura et al. J Antimicrob Chemother 2019: 74: 931–934). Although most GBS-RBS isolates were recovered from respiratory specimens from adults, particularly older adults, we obtained 5 GBS-RBS isolates from vaginal swabs of pregnant women in Japan (H. Moroi et al. Emerg Microbes Infect 2019: 8(1): 2–7).
Recently, we also reported on clinical isolates of group A Streptococcus (GAS) that harbor amino acid substitutions in PBPs (T. Ikeda, R. Suzuki et al. Antimicrob Agents Chemother 2021: 65(12): e0148221).
Continuous and careful monitoring of the drug susceptibilities of GBS and GAS is needed worldwide.