Two different types of hypervirulent K. pneumoniae (HvKp), the MLST-11 and serotype K1/K2 strains, have been frequently described in recent studies. Although these two types of strains were described to be HvKp, their virulence was not compared. In this study, in vitro and in vivo approaches were used to assess differences in virulence. A total of twenty-nine isolates, including 6 strains of each of serotype K1 and K2 isolates and 17 strains of ST11 isolates, were selected for this study. Phenotypic tests of virulence were performed by the string test and analysis of the virulent associated genes was detected by PCR. In vitro models of serum resistance and phagocytosis were used as the parameters to assess the virulence. In-frame deletion of virulence-associated genes was performed to study their contributions to virulence. The median lethal dose, i.e., the LD50, in mice was determined following IP injection. Although serotype K1 and K2 strains and ST11 isolates had similar virulence gene profiles, the ST11 isolates showed less serum and phagocytic resistance than the serotype K1/K2 isolates. The mouse lethality test revealed that all ST11 isolates were unable to cause lethality, even at > 107 CFU, while serotypes K1 and K2 showed an LD50 at ≤ 103 CFU. Aerobactin or capsule knockout mutants exhibited a lower LD50 than the parental strain, while capsule mutants showed a more significant decrease in LD50. Since there was a significant difference in virulence levels between the two types of HvKp when assessed in in vitro and in vivo models, it may be better to use the designation "HvKp" for some strains based on animal studies to avoid confusion. Virulence and non-virulence could be analysed in a relative manner, especially in comparison studies.

中文翻译：

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多基因座序列型 (MLST)-11、血清型 K1 或 K2 菌株的不同类型高毒力肺炎克雷伯菌之间的毒力

最近的研究中经常描述两种不同类型的高毒力肺炎克雷伯菌 (HvKp)，即 MLST-11 和血清型 K1/K2 菌株。尽管这两种类型的菌株被描述为 HvKp，但没有比较它们的毒力。在这项研究中，体外和体内方法用于评估毒力的差异。本研究共选择了 29 株分离株，包括血清型 K1 和 K2 分离株各 6 株，ST11 株各 17 株。毒力的表型测试通过字符串测试进行，毒力相关基因的分析通过PCR检测。血清抗性和吞噬作用的体外模型用作评估毒力的参数。进行毒力相关基因的框内删除以研究它们对毒力的贡献。中位致死剂量，即，在 IP 注射后测定小鼠的 LD50。尽管血清型 K1 和 K2 菌株和 ST11 分离株具有相似的毒力基因谱，但与血清型 K1/K2 分离株相比，ST11 分离株显示出较低的血清和吞噬细胞抗性。小鼠致死率测试表明，即使在 > 107 CFU 时，所有 ST11 分离株都无法引起致死性，而血清型 K1 和 K2 显示 LD50 ≤ 103 CFU。Aerobactin 或荚膜敲除突变体表现出比亲本菌株更低的 LD50，而荚膜突变体表现出更显着的 LD50 降低。由于在体外和体内模型中评估两种类型的 HvKp 之间的毒力水平存在显着差异，因此根据动物研究对某些菌株使用名称“HvKp”可能会更好，以避免混淆。