Population-level transition of capsular polysaccharide types among sequence type 1 group B Streptococcus isolates with reduced penicillin susceptibility during a long-term hospital epidemic.

2018 Fiscal Year Final Research Report

• Project/Area Number: 15K09566
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Research Field: Infectious disease medicine
• Research Institution: Shinshu University
• Principal Investigator: Nagano Noriyuki 信州大学, 学術研究院保健学系, 教授 (00747371)
• Co-Investigator(Kenkyū-buntansha): 小穴 こず枝 信州大学, 学術研究院保健学系, 准教授 (60115334)
• Project Period (FY): 2015-04-01 – 2019-03-31
• Keywords: B群レンサ球菌 / PRGBS / 莢膜スイッチング / CTBrPSGBS / ワクチン戦略

Outline of Final Research Achievements

Group B Streptococcus isolates with reduced penicillin susceptibility (PRGBS) were detected from elderly patients, accompanying population-level transition of serotypes during a long-term hospital epidemic. Serotype III predominated in the first 9 months, which was replaced predominantly by serotype Ia for 9 months. Serotypes III and Ia isolates, belonging to ST1, shared four substitutions in penicillin-binding protein 2X. WGS revealed that the serotype III strain SU12 had a higher degree of genomic similarity with serotype Ia strain SU97. Moreover, the sequence characteristics of the disruption of the hyaluronidase gene located upstream of cpsY by insertion of IS1548 in strain SU12 and the insertion of ΔISSag8 between tRNA-Arg and rpsA genes located downstream of cpsL in strain SU97 were shared by other serotype III and Ia isolates, respectively. Capsular switching and nosocomial transmission may possibly contribute to population-level serotype replacement among ST1 PRGBS isolates.

Free Research Field

臨床微生物の薬剤耐性機構

Academic Significance and Societal Importance of the Research Achievements

PRGBSにおける莢膜スイッチングを促す要因として、抗菌薬によるbacterial stressや宿主の抗莢膜抗体による免疫圧が考えられる。莢膜スイッチング事象によりGBSが宿主抗体による免疫防御を回避する可能性は、WHO主導で進行中のワクチン開発戦略における障壁となることから本成果をInt J Antimicrob Agents 2019;53:203-210にて発表した。
また、選択圧となるβ-ラクタム剤の違いによって選択される耐性株がPRGBS株あるいはCTBrPSGBS株と異なる危険性を見出し、Microbiol Immunol 2019;63:65-76にて報告した。