Over a 35-month period, group B Streptococcus isolates with reduced penicillin susceptibility (PRGBS) were detected from elderly patients at a regional hospital in Japan, accompanying population-level transition of PRGBS serotypes. The genetic relatedness of 77 non-duplicate PRGBS from 73 patients was analysed. Serotype III PRGBS predominated (16 serotype III/1 serotype Ib) in the first 9 months (period I), then 3 serotype Ib isolates appeared transiently for the next 3 months (period II), which was replaced predominantly by serotype Ia (20 serotype Ia/1 serotype III/1 non-typeable) for 9 months (period III). In the last 14 months (period IV), besides 25 serotype Ia isolates, 10 serotype III were also identified. Serotypes III and Ia isolates, belonging to ST1, shared G329V, G398A, V405A and G429D substitutions in penicillin-binding protein 2X. Of three strains subjected to whole-genome sequencing, serotype III strain SU12 (period I) had a higher degree of genomic similarity with serotype Ia strain SU97 (period III) than serotype Ib strain SU67 (period II) based on average nucleotide identity and single nucleotide polymorphisms. Analysis of the cps gene clusters and the upstream and downstream flanking sequences revealed that disruption of the hyaluronidase gene located upstream of cpsY by insertion of IS1548 was found in strain SU12, whereas ΔISSag8 was inserted between tRNA-Arg and rpsA genes located downstream of cpsL in strain SU97. Interestingly, most serotype III PRGBS re-emerging in period IV had this tRNA-Arg–ΔISSag8–rpsA region. Capsular switching and nosocomial transmission may possibly contribute to population-level serotype replacement among ST1 PRGBS isolates.
All Science Journal Classification (ASJC) codes
- Microbiology (medical)
- Infectious Diseases
- Pharmacology (medical)