Veterans Administration Western New York Healthcare System, Buffalo, New York, USA.
Infect Immun. 2014 Jun;82(6):2356-67. doi: 10.1128/IAI.01667-13. Epub 2014 Mar 24.
Hypervirulent (hypermucoviscous) Klebsiella pneumoniae (hvKP) strains are an emerging variant of "classical" K. pneumoniae (cKP) that cause organ and life-threatening infection in healthy individuals. An understanding of hvKP-specific virulence mechanisms that enabled evolution from cKP is limited. Observations by our group and previously published molecular epidemiologic data led us to hypothesize that hvKP strains produced more siderophores than cKP strains and that this trait enhanced hvKP virulence. Quantitative analysis of 12 hvKP strains in iron-poor minimal medium or human ascites fluid showed a significant and distinguishing 6- to 10-fold increase in siderophore production compared to that for 14 cKP strains. Surprisingly, high-pressure liquid chromatography (HPLC)-mass spectrometry and characterization of the hvKP strains hvKP1, A1142, and A1365 and their isogenic aerobactin-deficient (ΔiucA) derivatives established that aerobactin accounted for the overwhelming majority of increased siderophore production and that this was not due to gene copy number. Further, aerobactin was the primary factor in conditioned medium that enhanced the growth/survival of hvKP1 in human ascites fluid. Importantly the ex vivo growth/survival of hvKP1 ΔiucA was significantly less than that of hvKP1 in human ascites fluid, and the survival of outbred CD1 mice challenged subcutaneously or intraperitoneally with hvKP1 was significantly less than that of mice challenged with hvKP1 ΔiucA. The lowest subcutaneous and intraperitoneal challenge inocula of 3 × 10(2) and 3.2 × 10(1) CFU, respectively, resulted in 100% mortality, demonstrating the virulence of hvKP1 and its ability to cause infection at a low dose. These data strongly support that aerobactin accounts for increased siderophore production in hvKP compared to cKP (a potential defining trait) and is an important virulence factor.
高毒力（高黏液性）肺炎克雷伯菌（hvKP）菌株是“经典”肺炎克雷伯菌（cKP）的一种新兴变体，可导致健康个体发生器官和危及生命的感染。对 hvKP 特定毒力机制的了解有限，这些机制使它们能够从 cKP 进化而来。我们小组的观察结果和之前发表的分子流行病学数据使我们假设 hvKP 菌株比 cKP 菌株产生更多的铁载体，并且这种特性增强了 hvKP 的毒力。在缺铁贫化最小培养基或人腹水液中对 12 株 hvKP 菌株进行定量分析显示，与 14 株 cKP 菌株相比，铁载体的产量显著增加了 6 至 10 倍。令人惊讶的是，高效液相色谱（HPLC）-质谱分析和 hvKP 菌株 hvKP1、A1142 和 A1365 及其同源的aerobactin 缺陷（ΔiucA）衍生物的表征表明，aerobactin 占增加的铁载体产量的绝大多数，并且这不是由于基因拷贝数。此外，aerobactin 是增强 hvKP1 在人腹水中生长/存活的条件培养基中的主要因素。重要的是，hvKP1 ΔiucA 的体外生长/存活明显低于 hvKP1 在人腹水中的生长/存活，而用 hvKP1 皮下或腹腔挑战的杂交 CD1 小鼠的存活率明显低于用 hvKP1 ΔiucA 挑战的小鼠。最低的皮下和腹腔挑战接种量分别为 3×102 和 3.2×101 CFU，导致 100%的死亡率，表明了 hvKP1 的毒力及其能够以低剂量引起感染的能力。这些数据强烈支持 aerobactin 占 hvKP 比 cKP 增加的铁载体产生（一个潜在的定义特征），并且是一个重要的毒力因素。
