Department of Microbiology, Tokyo Medical University, Tokyo, Japan.
Department of Microbiology, Tokyo Medical University, Tokyo, Japan; Department of General Medicine, Keio University School of Medicine, Tokyo, Japan.
J Infect Chemother. 2022 Nov;28(11):1523-1530. doi: 10.1016/j.jiac.2022.08.006. Epub 2022 Aug 11.
In Japan, the introduction of pneumococcal conjugate vaccine (PCV) in children has decreased vaccine-type (VT) pneumococcal infections caused by penicillin (PEN)-non-susceptible Streptococcus pneumoniae. PEN-non-susceptible strains have gradually emerged among non-vaccine types (NVT). In this study, we aim to investigate the pbp gene mutations and the characteristics of PEN-binding proteins (PBPs) that mediate PEN resistance in NVT strains.
Pneumococcal 41 strains of NVT isolated from patients with invasive pneumococcal infection were randomly selected. Nucleotide sequences for pbp genes encoding PBP1A, PBP2X, and PBP2B were analyzed, and amino acid (AA) substitutions that contribute to β-lactam resistance were identified. In addition, the three-dimensional (3D) structure of abnormal PBPs in the resistant strain was compared with that of a reference R6 strain via homology modeling.
In PEN-non-susceptible NVT strains, Thr to Ala or Ser substitutions in the conserved AA motif (STMK) were important in PBP1A and PBP2X. In PBP2B, substitutions from Thr to Ala, adjacent to the SSN motif, and from Glu to Gly were essential. The 3D structure modeling indicated that AA substitutions are characterized by accumulation around the enzymatic active pocket in PBPs. Many AA substitutions detected throughout the PBP domains were not associated with resistance, except for AA substitutions in or adjacent to AA motifs. Clonal complexes and sequence types showed that almost all NVT cases originated in other countries and spread to Japan via repeat mutations.
NVT with diverse AA substitutions increased gradually with pressure from both antimicrobial agents and vaccines.
在日本，儿童型肺炎球菌结合疫苗（PCV）的引入降低了青霉素（PEN）不敏感肺炎链球菌引起的疫苗型（VT）肺炎球菌感染。PEN 不敏感株逐渐出现在非疫苗型（NVT）中。本研究旨在研究 NVT 株中介导 PEN 耐药的 pbp 基因突变和 PEN 结合蛋白（PBP）的特性。
随机选择 41 株来自侵袭性肺炎球菌感染患者的 NVT 肺炎球菌。分析编码 PBP1A、PBP2X 和 PBP2B 的 pbp 基因的核苷酸序列，并确定导致β-内酰胺耐药的氨基酸（AA）取代。此外，通过同源建模比较耐药株中异常 PBP 的三维（3D）结构与参考 R6 株的结构。
在 PEN 不敏感的 NVT 菌株中，PBP1A 和 PBP2X 中保守 AA 基序（STMK）中的 Thr 到 Ala 或 Ser 取代是重要的。在 PBP2B 中，位于 SSN 基序附近的 Thr 到 Ala 和 Glu 到 Gly 的取代是必需的。3D 结构建模表明，AA 取代的特征是在 PBPs 的酶活性口袋周围积累。除了 AA 基序中的或附近的 AA 取代外，在 PBP 结构域中检测到的许多 AA 取代与耐药性无关。克隆复合物和序列类型表明，几乎所有的 NVT 病例都源自其他国家，并通过重复突变传播到日本。
在抗菌药物和疫苗的压力下，具有多种 AA 取代的 NVT 逐渐增加。
