<i>Galleria mellonella -</i> a novel infection model for the <i>Mycobacterium tuberculosis</i> complex

Animal models have long been used in tuberculosis research to understand disease pathogenesis and to evaluate novel vaccine candidates and anti-mycobacterial drugs. However, all have limitations and there is no single animal model which mimics all the aspects of mycobacterial pathogenesis seen in humans. Importantly mice, the most commonly used model, do not normally form granulomas, the hallmark of tuberculosis infection. Thus there is an urgent need for the development of new alternative <i>in vivo</i> models. The insect larvae, <i>Galleria mellonella</i> has been increasingly used as a successful, simple, widely available and cost-effective model to study microbial infections. Here we report for the first time that <i>G. mellonella</i> can be used as an infection model for members of the <i>Mycobacterium tuberculosis</i> complex. We demonstrate a dose-response for <i>G. mellonella</i> survival infected with different inocula of bioluminescent <i>Mycobacterium bovis</i> BCG <i>lux</i>, and demonstrate suppression of mycobacterial luminesence over 14 days. Histopathology staining and transmission electron microscopy of infected <i>G. mellonella</i> phagocytic haemocytes show internalization and aggregation of <i>M. bovis</i> BCG <i>lux</i> in granuloma-like structures, and increasing accumulation of lipid bodies within <i>M. bovis</i> BCG <i>lux</i> over time, characteristic of latent tuberculosis infection. Our results demonstrate <i>that G. mellonella</i> can act as a surrogate host to study the pathogenesis of mycobacterial infection and shed light on host-mycobacteria interactions, including latent tuberculosis infection.长期以来，动物模型被应用于结核病（tuberculosis）研究中，以阐明疾病发病机制（pathogenesis），并评估新型候选疫苗与抗分枝杆菌（Mycobacterium）药物。然而，所有动物模型均存在局限性，目前尚无任何一种动物模型能够复现人类感染分枝杆菌时的全部发病特征。尤为关键的是，作为最常用的动物模型，小鼠通常无法形成结核病感染的标志性病理特征——肉芽肿（granuloma）。因此，迫切需要开发新型替代性<i>体内（in vivo）</i>研究模型。昆虫幼虫大蜡螟（Galleria mellonella）作为一种高效、简便、易获取且成本低廉的微生物感染研究模型，其应用正日益广泛。本研究首次证实，大蜡螟可作为结核分枝杆菌复合群（Mycobacterium tuberculosis complex）感染的研究模型。我们观察到，感染不同接种剂量的生物发光型牛分枝杆菌卡介苗（Mycobacterium bovis BCG）<i>lux</i>后，大蜡螟的存活率呈现剂量依赖性特征，并证实分枝杆菌的发光信号在14天内被逐步抑制。通过对感染后的大蜡螟吞噬性血细胞进行组织病理学染色与透射电子显微镜（transmission electron microscopy）观察，我们发现牛分枝杆菌卡介苗<i>lux</i>被内化并聚集形成类肉芽肿结构，且随着时间推移，牛分枝杆菌卡介苗<i>lux</i>胞内脂滴积累逐渐增多，这正是潜伏性结核病感染（latent tuberculosis infection）的典型特征。本研究结果证实，大蜡螟可作为替代宿主，用于研究分枝杆菌感染的发病机制，并为解析宿主-分枝杆菌互作（包括潜伏性结核病感染）提供新的研究视角。