Wei Da-Wei, Song Yuqin, Li Yi, Zhang Gang, Chen Qi, Wu Linhuan, Huang Jiangqing, Tian Xueru, Wang Chao, Feng Jie
State Key Laboratory of Microbial Diversity and Innovative Utilization, Institute of Microbiology, Chinese Academy of Sciences, Beijing, China.
College of Life Science, University of Chinese Academy of Sciences, Beijing, China.
Genome Med. 2025 May 6;17(1):45. doi: 10.1186/s13073-025-01474-0.
The convergence of resistance and hypervirulence in Klebsiella pneumoniae represents a significant public health threat, driven by the horizontal transfer of plasmids. Understanding factors affecting plasmid transfer efficiency is essential to elucidate mechanisms behind emergence of these formidable pathogens.
Hypermucoviscous K. pneumoniae strains were serially passaged in LB medium to investigate capsule-deficient phenotypes. Capsule-deficient mutants were analyzed using genetic sequencing to identify the types and insertion sites of insertion sequences (IS). Bioinformatics and statistical analyses based on the NCBI and National Microbiology Data Center (NMDC) database were used to map the origins and locations of IS elements. Conjugation assays were performed to assess plasmid transfer efficiency between encapsulated and capsule-deficient strains. A murine intestinal colonization model was employed to evaluate virulence levels and IS excision-mediated capsule restoration.
Our research revealed that a hypervirulent K. pneumoniae (hvKP) strain acquired a bla-bearing IncX3 plasmid with IS5 and ISKox3 elements. These IS elements are capable of inserting into capsular polysaccharide synthesis genes, causing a notably high frequency of capsule loss in vitro. The IS-mediated capsular phase variation, whether occurring in the donor or recipient strain, significantly increased the conjugation frequency of both the resistance plasmid and the virulence plasmid. Additionally, capsular phase variation enhanced bacterial adaptability in vitro. Experiments in mouse models demonstrated that capsule-deficient mutants exhibited reduced virulence and colonization capacity. However, during long-term intestinal colonization, IS element excision restored capsule expression, leading to the recovery of hypervirulence and enhanced colonization efficiency.
Our findings reveal that IS elements mediate capsular phase variation by toggling gene activity, accelerating the genomic convergence of multidrug resistance and hypervirulence in K. pneumoniae, as well as facilitating adaptive transitions in different environments.
肺炎克雷伯菌中耐药性与高毒力的融合是一个重大的公共卫生威胁，由质粒的水平转移驱动。了解影响质粒转移效率的因素对于阐明这些可怕病原体出现背后的机制至关重要。
将高黏液型肺炎克雷伯菌菌株在LB培养基中连续传代，以研究无荚膜表型。使用基因测序分析无荚膜突变体，以鉴定插入序列（IS）的类型和插入位点。基于NCBI和国家微生物数据中心（NMDC）数据库进行生物信息学和统计分析，以绘制IS元件的起源和位置。进行接合试验以评估有荚膜菌株和无荚膜菌株之间的质粒转移效率。采用小鼠肠道定植模型评估毒力水平和IS切除介导的荚膜恢复。
我们的研究表明，一株高毒力肺炎克雷伯菌（hvKP）菌株获得了一个携带bla的IncX3质粒，该质粒带有IS5和ISKox3元件。这些IS元件能够插入荚膜多糖合成基因，导致体外荚膜丢失的频率显著升高。IS介导的荚膜相变，无论发生在供体菌株还是受体菌株中，都显著增加了耐药质粒和毒力质粒的接合频率。此外，荚膜相变增强了细菌在体外的适应性。小鼠模型实验表明，无荚膜突变体的毒力和定植能力降低。然而，在长期肠道定植过程中，IS元件切除恢复了荚膜表达，导致高毒力恢复和定植效率提高。
我们的研究结果表明，IS元件通过切换基因活性介导荚膜相变，加速了肺炎克雷伯菌多药耐药性和高毒力的基因组融合，并促进了在不同环境中的适应性转变。
