T4SS C型分泌系统在肺炎链球菌形成新耐药岛中的机制研究

Rapidly increasing prevalence of Streptococcus pneumoniae resistant to antibiotics deactivating the clinical treatment makes it becomes one of the most critical problems in clinic. Differ to the traditional vertical transfer of resistance mutations, the horizontal transfer of resistance genes may be related to fast emerging of the antibiotic resistant strains. Type IV secretion system (T4SS) was the only one secretion system that can mediate the transfer of DNA molecular, and was recognized as an important path of horizontal gene transfer in Gram negative bacteria. Our team has validated that T4SS also presents in Gram positive bacteria (e.g., Streptococcus suis) and named it as T4SS C subtype. In previous study, we discovered a genomic island in the genomes of multi-antibiotic resistant strains of S. pneumoniae, which carries both T4SS C and resistance genes. Thus, we hypothesized that T4SS C is the key component of a new resistance island in S. pneumoniae, which can mediate the horizontal transfer of resistance genes and play an important role in the generation of new resistance strains. To test this hypothesis, we plan to perform functional validation in standard strains to confirm the functions of key T4SS C genes in forming, transferring and integration of this island. Furthermore, we intend to perform molecular epidemiological study in clinical isolates to compare the composition and transfer efficiency of different types of T4SS C islands. Our study would expand the knowledge about mechanism of T4SS C in forming new resistance island and mediating resistance gene transfer, which could provide scientific basis for explaining the clinical problem of rapid emerging of resistant strains.

肺炎链球菌多重耐药现象日趋严重，已成为当前临床面临的严峻挑战。最近研究表明这种快速获得的耐药性与耐药基因横向转移密切相关。四型分泌系统是横向基因转移的重要途径之一，是唯一可外排DNA分子的分泌系统。既往认为只存在于革兰氏阴性菌，本团队首次发现革兰氏阳性菌（猪链球菌）存在该系统并称作为C亚型（T4SS C），得到国际关注和认可，但其是否参与耐药基因的横向转移并导致耐药性扩散尚不清楚。申请人预实验发现：部分肺炎链球菌携带T4SS C和耐药基因构成的新型耐药岛。据此推测：肺炎链球菌T4SS C是耐药基因传递和新型耐药菌产生的重要分子机制。本研究拟在肺炎链球菌模式株中验证T4SS C在耐药岛形成和横向转移中的关键作用；在临床患者菌株中进行流行病学研究，比较不同类型菌株间T4SS C耐药岛的构成情况和转移效率，为解释“耐药菌株快速出现”这一临床问题提供科学依据。

肺炎链球菌多重耐药现象日趋严重，已成为当前临床面临的严峻挑战。研究表明这种快速获得的耐药性与耐药基因横向转移密切相关。四型分泌系统（Type IV secretion system, T4SS）是横向基因转移的重要途径之一，是唯一可外排DNA分子的细菌分泌系统。既往认为T4SS只存在于革兰氏阴性菌，本团队首次发现革兰氏阳性菌（猪链球菌）存在该系统并称作为C亚型（T4SS C），得到国际关注和认可，但其是否参与肺炎链球菌中耐药基因的横向转移并导致耐药性扩散此前尚不清楚。本项目通过对课题组前期研究发现的肺炎链球菌基因组编码的T4SS C和耐药基因构成的新型耐药岛开展了深入研究，在肺炎链球菌模式株中验证了T4SS C在耐药岛形成和横向转移中的关键作用，明确了该耐药岛可通过T4SS C接合转移并发现了关键基因元件virD4、virB6和oriT等；在公共数据和临床菌株中开展了基因组差异分析和流行病学研究，比较不同菌株间T4SS C耐药岛的构成情况、耐药岛的核心基因构成以及相关耐药基因，为解释“肺炎链球菌耐药菌株快速出现”这一临床问题提供了科学依据，证明了肺炎链球菌T4SS C是耐药基因传递和新型耐药菌产生的重要分子机制。