Kabha K, Nissimov L, Athamna A, Keisari Y, Parolis H, Parolis L A, Grue R M, Schlepper-Schafer J, Ezekowitz A R, Ohman D E
Department of Human Microbiology, Sackler Faculty of Medicine, Tel-Aviv University, Israel.
Infect Immun. 1995 Mar;63(3):847-52. doi: 10.1128/iai.63.3.847-852.1995.
Klebsiella pneumoniae strains of the K2 capsular serotype are usually highly virulent in mice, which is in contrast to the low virulence of most other serotypes. Here we used a genetic approach to examine the relative contribution of capsule type to the virulence of K. pneumoniae in mice. We used wild-type strains expressing capsular polysaccharide (CPS) serotypes K2 (strain KPA1) and K21a (strains KPB1 and KPC1), which were then used to construct capsule-switched derivatives. The close proximity of the cps gene cluster to selectable his markers made it possible to mobilize the cps genes by conjugation from one serotype (donor) to another (recipient) and to obtain recombinants in which interserotype switching had occurred by reciprocal recombination. Each capsule-switched derivative examined of the KPA and KPC strain backgrounds produced a CPS that was immunologically and structurally identical to that of the donor. Strain background was confirmed by demonstrating restriction fragment length polymorphism patterns identical to those of the respective recipients. The parent strains were then compared with capsule-switched recombinants for phenotypic properties associated with virulence. Clearance from the bloodstreams of mice was rapid in serotype K21a strains of either wild-type or recombinant origin, whereas K2 strains remained viable in the blood during the period examined. These differences appeared to be dependent upon the CPS type but independent of strain background. Binding to macrophages was higher in K21a strains than in those with the K2 capsule and was also independent of the strain background. Both blood clearance and macrophage-binding activities were completely inhibited by yeast mannan, suggesting that they were mediated via the macrophage mannose receptor. The K2 parent strain was highly virulent to mice (50% lethal dose [LD50], 3 x 10(3)), while the K21a parent strains demonstrated low virulence (LD50, > 2 x 10(8)). Interestingly, the virulence of recombinant KPC10(cpsK2), originally of the KPC1(cpsK21a) background, was intermediate (LD50, 4 x 10(5)). In contrast, both cpsK21a recombinants of the originally virulent KPA1 (cpsK2) background became nearly avirulent (LD50, > 2 x 10(8)). Six additional serotypes (K12, K24, K32, K55, K62, and K67) were examined, and all showed a positive correlation between the ability of the Klebsiella serotype to interact with a human mannose receptor, as expressed by Cos I cell recombinants, and the LD50 of the serotype. These results suggest that expression of a capsule which is recognized by the mannose receptor markedly affects the interaction with macrophages and blood clearance.(ABSTRACT TRUNCATED AT 400 WORDS)
K2荚膜血清型的肺炎克雷伯菌菌株通常对小鼠具有高度毒性，这与大多数其他血清型的低毒性形成对比。在此，我们采用遗传学方法来研究荚膜类型对肺炎克雷伯菌在小鼠体内毒性的相对贡献。我们使用表达荚膜多糖（CPS）血清型K2（菌株KPA1）和K21a（菌株KPB1和KPC1）的野生型菌株，然后用它们构建荚膜转换衍生物。cps基因簇与可选择的组氨酸标记紧密相邻，这使得通过接合作用将cps基因从一种血清型（供体）转移到另一种血清型（受体）并获得通过相互重组发生血清型转换的重组体成为可能。对KPA和KPC菌株背景的每个荚膜转换衍生物进行检测，结果显示其产生的CPS在免疫学和结构上与供体的CPS相同。通过证明限制片段长度多态性模式与各自受体的模式相同来确认菌株背景。然后将亲本菌株与荚膜转换重组体进行与毒性相关的表型特性比较。野生型或重组来源的血清型K21a菌株在小鼠血流中的清除速度很快，而K2菌株在所检测的时间段内在血液中仍保持存活。这些差异似乎取决于CPS类型，但与菌株背景无关。K21a菌株与巨噬细胞的结合高于具有K2荚膜的菌株，并且也与菌株背景无关。血液清除和巨噬细胞结合活性均被酵母甘露聚糖完全抑制，这表明它们是通过巨噬细胞甘露糖受体介导的。K2亲本菌株对小鼠具有高度毒性（半数致死剂量[LD50]，3×10³），而K21a亲本菌株显示出低毒性（LD50，>2×10⁸）。有趣的是，最初具有KPC1（cpsK21a）背景的重组KPC10（cpsK2）的毒性处于中间水平（LD50，4×10⁵）。相比之下，最初具有高毒性的KPA1（cpsK2）背景的两个cpsK21a重组体几乎变得无毒（LD50，>2×10⁸）。另外检测了六种血清型（K12、K24、K32、K55、K62和K67），所有这些血清型都显示，由Cos I细胞重组体所表达的肺炎克雷伯菌血清型与人类甘露糖受体相互作用的能力与该血清型的LD50之间存在正相关。这些结果表明，被甘露糖受体识别的荚膜的表达显著影响与巨噬细胞的相互作用和血液清除。（摘要截短至4**00词）
