Wheat William H, Casali Amy L, Thomas Vincent, Spencer John S, Lahiri Ramanuj, Williams Diana L, McDonnell Gerald E, Gonzalez-Juarrero Mercedes, Brennan Patrick J, Jackson Mary
Mycobacteria Research Laboratories, Department of Microbiology, Immunology and Pathology, Colorado State University, Fort Collins, Colorado, United States of America.
STERIS SA R&D, Fontenay-aux-Roses, France.
PLoS Negl Trop Dis. 2014 Dec 18;8(12):e3405. doi: 10.1371/journal.pntd.0003405. eCollection 2014 Dec.
Leprosy is a curable neglected disease of humans caused by Mycobacterium leprae that affects the skin and peripheral nerves and manifests clinically in various forms ranging from self-resolving, tuberculoid leprosy to lepromatous leprosy having significant pathology with ensuing disfiguration disability and social stigma. Despite the global success of multi-drug therapy (MDT), incidences of clinical leprosy have been observed in individuals with no apparent exposure to other cases, suggestive of possible non-human sources of the bacteria. In this study we show that common free-living amoebae (FLA) can phagocytose M. leprae, and allow the bacillus to remain viable for up to 8 months within amoebic cysts. Viable bacilli were extracted from separate encysted cocultures comprising three common Acanthamoeba spp.: A. lenticulata, A. castellanii, and A. polyphaga and two strains of Hartmannella vermiformis. Trophozoites of these common FLA take up M. leprae by phagocytosis. M. leprae from infected trophozoites induced to encyst for long-term storage of the bacilli emerged viable by assessment of membrane integrity. The majority (80%) of mice that were injected with bacilli extracted from 35 day cocultures of encysted/excysted A. castellanii and A. polyphaga showed lesion development that was similar to mice challenged with fresh M. leprae from passage mice albeit at a slower initial rate. Mice challenged with coculture-extracted bacilli showed evidence of acid-fast bacteria and positive PCR signal for M. leprae. These data support the conclusion that M. leprae can remain viable long-term in environmentally ubiquitous FLA and retain virulence as assessed in the nu/nu mouse model. Additionally, this work supports the idea that M. leprae might be sustained in the environment between hosts in FLA and such residence in FLA may provide a macrophage-like niche contributing to the higher-than-expected rate of leprosy transmission despite a significant decrease in human reservoirs due to MDT.
麻风病是一种由麻风分枝杆菌引起的可治愈的被忽视的人类疾病，它会影响皮肤和周围神经，临床表现形式多样，从可自愈的结核样型麻风到瘤型麻风，后者具有严重病变，会导致毁容、残疾和社会耻辱。尽管多药疗法（MDT）在全球取得了成功，但在没有明显接触其他病例的个体中也观察到了临床麻风病的发病率，这表明细菌可能存在非人类来源。在本研究中，我们表明常见的自由生活阿米巴（FLA）可以吞噬麻风分枝杆菌，并使该杆菌在阿米巴囊肿内存活长达8个月。从分别包含三种常见棘阿米巴属物种（扁豆棘阿米巴、卡氏棘阿米巴和多食棘阿米巴）以及两株蠕虫状哈特曼阿米巴的包囊共培养物中提取出了活的杆菌。这些常见FLA的滋养体通过吞噬作用摄取麻风分枝杆菌。通过评估膜完整性，发现来自被诱导形成包囊以长期储存杆菌的受感染滋养体的麻风分枝杆菌仍具有活力。注射从卡氏棘阿米巴和多食棘阿米巴35天的包囊/脱囊共培养物中提取的杆菌的大多数（80%）小鼠出现了病变发展，这与用传代小鼠新鲜麻风分枝杆菌攻击的小鼠相似，尽管初始速度较慢。用共培养物提取的杆菌攻击的小鼠显示出抗酸细菌的证据以及麻风分枝杆菌的阳性PCR信号。这些数据支持了以下结论：麻风分枝杆菌可以在环境中普遍存在的FLA中长期存活，并如在无胸腺裸鼠模型中评估的那样保持毒力。此外，这项工作支持了这样一种观点，即麻风分枝杆菌可能在宿主之间的环境中由FLA维持，并且在FLA中的这种存活可能提供一个类似巨噬细胞的生态位，尽管由于MDT人类传染源显著减少，但仍导致高于预期的麻风病传播率。
