Institute of Parasitology, University of Bern, Länggassstrasse 122, CH-3012 Bern, Switzerland.
Biology Division, Spiez Laboratory, Federal Office for Civil Protection, Austrasse, CH-3700 Spiez, Switzerland.
Microbiology (Reading). 2012 Oct;158(Pt 10):2652-2660. doi: 10.1099/mic.0.059790-0. Epub 2012 Aug 9.
Species in the genus Naegleria are free-living amoebae of the soil and warm fresh water. Although around 30 species have been recognized, Naegleria fowleri is the only one that causes primary amoebic meningoencephalitis (PAM) in humans. PAM is an acute and fast progressing disease affecting the central nervous system. Most of the patients die within 1-2 weeks of exposure to the infectious water source. The fact that N. fowleri causes such fast progressing and highly lethal infections has opened many questions regarding the relevant pathogenicity factors of the amoeba. In order to investigate the pathogenesis of N. fowleri under defined experimental conditions, we developed a novel high- versus low-pathogenicity model for this pathogen. We showed that the composition of the axenic growth media influenced growth behaviour and morphology, as well as in vitro cytotoxicity and in vivo pathogenicity of N. fowleri. Trophozoites maintained in Nelson's medium were highly pathogenic for mice, demonstrated rapid in vitro proliferation, characteristic expression of surface membrane vesicles and a small cell diameter, and killed target mouse fibroblasts by both contact-dependent and -independent destruction. In contrast, N. fowleri cultured in PYNFH medium exhibited a low pathogenicity, slower growth, increased cell size and contact-dependent target cell destruction. However, cultivation of the amoeba in PYNFH medium supplemented with liver hydrolysate (LH) resulted in trophozoites that were highly pathogenic in mice, and demonstrated an intermediate proliferation rate in vitro, diminished cell diameter and contact-dependent target cell destruction. Thus, in this model, the presence of LH resulted in increased proliferation of trophozoites in vitro and enhanced pathogenicity of N. fowleri in mice. However, neither in vitro cytotoxicity mechanisms nor the presence of membrane vesicles on the surface correlated with the pathologic potential of the amoeba. This indicated that the pathogenicity of N. fowleri remains a complex interaction between as-yet-unidentified cellular mechanisms.
纳氏纳虫是土壤和温水环境中的自由生活阿米巴虫，虽然已识别出约 30 种，但只有福氏纳虫会导致人类原发性阿米巴脑膜脑炎（PAM）。PAM 是一种影响中枢神经系统的急性和快速进展性疾病。大多数患者在接触感染水源后 1-2 周内死亡。福氏纳虫引起如此快速进展和高度致命的感染这一事实引发了许多关于该阿米巴相关致病因素的问题。为了在明确的实验条件下研究福氏纳虫的发病机制，我们为该病原体开发了一种新型的高致病性与低致病性模型。我们发现，无共生生长培养基的组成会影响福氏纳虫的生长行为和形态，以及体外细胞毒性和体内致病性。在尼尔森培养基中维持的滋养体对小鼠具有高度致病性，表现出快速的体外增殖、特征性表达表面膜泡和较小的细胞直径，并通过接触依赖性和非接触依赖性破坏杀死靶鼠成纤维细胞。相比之下，在 PYNFH 培养基中培养的福氏纳虫表现出低致病性、较慢的生长速度、增加的细胞大小和接触依赖性的靶细胞破坏。然而，在 PYNFH 培养基中培养的阿米巴虫中添加肝水解物（LH）会导致在小鼠中具有高致病性的滋养体，并且在体外表现出中等增殖率、减小的细胞直径和接触依赖性的靶细胞破坏。因此，在该模型中，LH 的存在导致体外滋养体的增殖增加，以及福氏纳虫在小鼠中的致病性增强。然而，体外细胞毒性机制或表面膜泡的存在均与阿米巴的病理潜力无关。这表明福氏纳虫的致病性仍然是尚未识别的细胞机制之间的复杂相互作用。
