Department of Biological Sciences, Birla Institute of Technology and Science, Pilani, 333031, Rajasthan, India.
Department of Biological Sciences, Birla Institute of Technology and Science, Pilani, 333031, Rajasthan, India.
Microb Pathog. 2020 Nov;148:104449. doi: 10.1016/j.micpath.2020.104449. Epub 2020 Aug 14.
Enterobacter cloacae, an opportunistic nosocomial pathogen, is reported to possess different virulence factors that could potentially influence its pathogenesis. Generally, the E. cloacae infections are of endogenous origin occurring in immunocompromised patients. The mechanisms of pathogenicity remain elusive, possibly due to the absence of established model hosts. Thus, we explored the utility of Caenorhabditis elegans as a model host to test the pathogenicity of E. cloacae SBP-8, a soil isolate. E. cloacae SBP-8 progressively colonized the intestine of C. elegans. It induced cell death (as assessed through DNA damage), reproductive defect and reduction of lifespan, comparable to a clinical isolate, E. cloacae (MTCC 509). Observation with Nomarski microscopy revealed significant anterior pharyngeal distention, and altered egg arrangement with internal egg hatching in 70% infected worms. The internal egg hatching was observed as early as 48 h post infection. E. cloacae SBP-8 infection reduced the brood size by 16%. A 2',7'-dichlorodihydrofluorescein diacetate staining confirmed the 10-fold induction of reactive oxygen species implicating either mitochondrial damage or septic shock in infected worms. Expression analysis through RT-PCR indicated stimulation of immune response by E. cloacae SBP-8 in worms by upregulating tol-1, a Toll-like receptor, within 6 h of exposure. During the initial phase of infection (up to 24 h) the nematodes exhibited protective immune response by upregulating antimicrobial peptide genes, lys-1, clec-60, clec-85, and clec-87. However, these genes were downregulated at later hours (48 h), indicating the nematodes surrendered to the infection. A similar trend was observed for reproductive genes (lin-29 and let-23), suggesting a struggle to maintain functional reproduction by the nematodes. These results clearly demonstrate the pathogenic potential of E. cloacae SBP-8 and suggest the suitability of C. elegans as a model organism to study its pathogenesis. This is the first study indicating that E. cloacae infections could potentially originate from an exogenic source (here soil).
阴沟肠杆菌是一种机会性病原体，据报道具有不同的毒力因子，这些因子可能影响其发病机制。通常，阴沟肠杆菌感染是内源性的，发生在免疫功能低下的患者中。其发病机制仍不清楚，可能是因为缺乏已建立的模式宿主。因此，我们探索了秀丽隐杆线虫作为模式宿主的实用性，以测试土壤分离株阴沟肠杆菌 SBP-8 的致病性。阴沟肠杆菌 SBP-8 逐渐定植于秀丽隐杆线虫的肠道。它诱导细胞死亡（通过 DNA 损伤评估）、生殖缺陷和寿命缩短，与临床分离株阴沟肠杆菌（MTCC 509）相当。诺马斯基显微镜观察显示，70%感染的蠕虫前咽显著扩张，卵排列改变，内部卵孵化。在感染后 48 小时即可观察到内部卵孵化。阴沟肠杆菌 SBP-8 感染使产卵量减少了 16%。2'，7'-二氯二氢荧光素二乙酸酯染色证实，活性氧的诱导增加了 10 倍，这表明感染的蠕虫中线粒体损伤或败血症休克。通过 RT-PCR 的表达分析表明，SBP-8 暴露 6 小时内，通过上调 Toll 样受体 tol-1，刺激线虫的免疫反应。在感染的初始阶段（最多 24 小时），线虫通过上调抗菌肽基因 lys-1、clec-60、clec-85 和 clec-87 来表现出保护性免疫反应。然而，这些基因在稍后的时间（48 小时）下调，表明线虫屈服于感染。生殖基因（lin-29 和 let-23）也出现了类似的趋势，表明线虫在努力维持功能性生殖。这些结果清楚地表明了阴沟肠杆菌 SBP-8 的致病潜力，并表明秀丽隐杆线虫适合作为研究其发病机制的模型生物。这是第一项表明阴沟肠杆菌感染可能来自外源性来源（这里是土壤）的研究。
