Pathogenic Diversity of Klebsiella pneumoniae Strains with Different Serotypes and Sequence Types from Human Liver Abscesses

Xue Ren^1,2Xuanfeng Liu^3,4Yujie Chen³Su An^3,4Bing Du³Hanqing Zhao^3,4Yanling Feng³Guanhua Xue³Jinghua Cui³Yuehua Ke³Lin Gan³Junxia Feng³Zheng Fan³Tongtong Fu³Ziying Xu³Zihui Yu³Yang Yang³Tingting Zhang³LEI HUANG^5*Chao Yan^3,4*Jing Yuan^3*

• ¹Capital Institute of Pediatrics, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing, China, Beijing, China
• ²Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China
• ³Children's Hospital of Capital Institute of Pediatrics, Beijing, China
• ⁴Capital Institute of Pediatrics, Beijing, China
• ⁵5th Medical Center of Chinese PLA General Hospital, Beijing, China

Klebsiella pneumoniae (K. pneumoniae) strains show diverse virulence phenotypes linked to serotype (K-type) and sequence type (ST), but the interplay between molecular characteristics and pathogenicity remains unclear. This study characterized 11 clinical K. pneumoniae strains from liver abscess patients, spanning various K-types (K1, K2, K5, K20, K57, K80), STs (including novel variants), and virulence factors. Phenotypic assays (growth curves, biofilm formation, TEM), antibiotic susceptibility testing (Vitek 2), and mouse infection models were combined with clinical data to assess virulence. Results revealed serotype/ST-associated virulence and short bacilli morphology, with 7 strains hypermucoviscosity-positive. Growth and biofilm phenotypes varied: K2-ST65 showed superior proliferation, K2-ST86 the weakest; K1-ST700 formed the strongest biofilm, K57-ST218 the weakest. Phylogenetic analysis (core SNPs from WGS) identified S5-105 and S5-036 as a distinct, highly differentiated clade. Antibiotic susceptibility was high (83.3% fully sensitive), with all strains susceptible to carbapenems, cephalosporins, aminoglycosides, and aztreonam; only S5-105 showed ciprofloxacin resistance/levofloxacin intermediate. Notably, novel STs exhibited unique pathogenicity: K1-novel ST caused rapid systemic infection (50% 72-h survival), severe liver abscesses, and neutrophilic inflammation; K80-novel ST selectively induced pulmonary abscesses without liver involvement, an atypical tropism. K2 virulence correlated with ST: hypervirulent K2-ST65 led to 50% survival, while K2-ST86 showed 100% survival. Other K-types had distinct effects: K20 caused liver damage, K57 was non-pathogenic, and slow-growing K5 induced mild injury. Conclusions highlight that specific K-type-ST combinations enhance lethality (e.g., K2-ST65), though effects are complex. Novel STs associate with acute lethality (K1) or atypical tropism (K80 lung-specific virulence), underscoring strain-specific mechanisms critical for infection risk stratification.