Functional impact of dietary chitin upon Listeria monocytogenes pathogenesis

Chitin, the second most abundant polymer in nature, is recognized for its biocompatibility and diverse effects on microbes and the host. Despite its potential, the role of chitin against foodborne pathogens such as Listeria monocytogenes remains underexplored. Here, we show that chitin functions as an environmental signal that attenuates L. monocytogenes virulence and mitigates infection outcomes. Consistent with previous in vitro studies, exposure of L. monocytogenes to chitin resulted in downregulation of key virulence genes, accompanied by reduced adhesion and invasion of intestinal epithelial cells. While chitin can act as a pathogen-associated molecular pattern (PAMP), stimulation of murine macrophages revealed no excessive induction of IL-6 or TNF-α after 24 hours, indicating that it does not provoke detrimental inflammatory responses. In vivo, dietary supplementation with chitin significantly reduced bacterial burden in faeces and secondary organs within 24 hours post-infection. These protective effects were further enhanced when mice were challenged with chitin-pretreated bacteria, highlighting the combined importance of host nutritional context and pathogen pre-exposure. Chitin also modulated host responses, promoting early IL-6 production and selectively shaping gut microbiota, with enrichment of beneficial genera such as Alistipes, Eubacterium, and Duncaniella and suppression of pro-inflammatory Prevotella. Transcriptomic analyses revealed that L. monocytogenes responds to chitin by upregulating virR and dltD, indicative of an envelope stress response, though no direct link to virulence gene downregulation was observed. Collectively, these findings establish chitin as a dietary and bioactive molecule that simultaneously modulates pathogen virulence, host immunity, and microbial ecology, representing a promising strategy to mitigate gastrointestinal infection.几丁质（Chitin）是自然界中含量第二丰富的聚合物，因其优异的生物相容性以及对微生物与宿主的多重调控效应而被广泛认可。尽管其应用潜力巨大，但几丁质抗食源性致病菌（如单核细胞增生李斯特菌，Listeria monocytogenes）的作用机制仍有待深入探究。本研究表明，几丁质可作为环境信号分子，削弱单核细胞增生李斯特菌的毒力并缓解感染结局。与既往体外研究结果一致，单核细胞增生李斯特菌经几丁质处理后，关键毒力基因表达显著下调，同时其对肠上皮细胞的黏附与侵袭能力显著降低。尽管几丁质可作为病原体相关分子模式（pathogen-associated molecular pattern, PAMP），但对小鼠巨噬细胞的体外刺激实验显示，24小时后并未引发IL-6与TNF-α的过度诱导，表明其不会诱发有害炎症反应。体内实验中，感染后24小时内，膳食补充几丁质可显著降低小鼠粪便及继发感染器官中的细菌载量。若使用经几丁质预处理的致病菌攻毒小鼠，上述保护效应会进一步增强，这凸显了宿主营养环境与致病菌预暴露的协同重要性。此外，几丁质可调控宿主免疫应答，促进IL-6的早期分泌，并选择性重塑肠道菌群结构：富集Alistipes、Eubacterium及Duncaniella等有益菌属，同时抑制促炎菌属Prevotella的增殖。转录组学分析显示，单核细胞增生李斯特菌可通过上调virR与dltD基因响应几丁质刺激，提示其存在包膜应激反应，但尚未发现该通路与毒力基因下调存在直接关联。综上，本研究证实几丁质是一种兼具膳食活性的生物活性分子，可同时调控致病菌毒力、宿主免疫与微生物生态，为缓解胃肠道感染提供了极具潜力的干预策略。