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单核细胞增生性李斯特氏菌Listeria monocytogenes是一种重要食源性人畜共患致病菌[1],侵入机体后可穿过肠道屏障,经淋巴和血液循环进入肝脏和脾脏,随后到达大脑和胎盘[2],引起败血症、脑膜炎以及早产或流产等症状[3]。单核细胞增生性李斯特氏菌广泛存在于牛奶、蔬菜和动物性食品等供应链中,由其引发的食物中毒病例逐年增多,虽然人类感染单核细胞增生李斯特氏菌发病率相对较低,但一旦感染死亡率可达30%~70%,占食源性病原菌感染死亡的半数以上[4]。单核细胞增生性李斯特氏菌分泌的胞外蛋白在细菌感染宿主中发挥着重要作用。细菌存在多种分泌系统将效应蛋白转运至胞外,其中双精氨酸转运系统(twinagininetranslocation,Tat)是运输完全折叠蛋白质的一种分泌系统[5]。
双精氨酸转运系统D (twinagininetranslocation D,TatD)是一种高度保守蛋白,广泛存在于微生物中,可作为一种重要的毒力因子参与修复DNA、降解胞外诱捕网和诱发细胞程序性凋亡[6]。伊氏锥虫Trypanosoma evansi和路氏锥虫Trypanosoma lewisi可分泌TatD蛋白,降解巨噬细胞胞外诱捕网以对抗宿主的固有免疫反应[7]。毛福超[8]研究发现:单核细胞增生性李斯特氏菌TatD重组蛋白具有核酸酶活性,同时通过重组自杀性质粒介导的等位基因交换技术获得了tatD基因缺失菌株(LM10403sΔtatD),但关于单核细胞增生性李斯特氏菌tatD基因对动物的毒力和肠道菌群影响仍不清楚。因此,本研究以小鼠Mus musculus为试验动物,将LM10403sΔtatD口服感染小鼠,观察tatD基因缺失后的单核细胞增生性李斯特氏菌对小鼠毒力和肠道菌群多样性的影响,为进一步探究tatD基因在单核细胞增生性李斯特氏菌与宿主互作中的具体作用以及减毒疫苗研究提供科学依据。
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从表1可见:小鼠经口服接种不同稀释含量的LM10403s、LM10403sΔtatD和LM10403sCΔtatD后,各组均有小鼠死亡,而无菌生理盐水对照组的小鼠均未发生死亡。PCR扩增鉴定死亡小鼠肝脏分离的细菌为单核细胞增生性李斯特氏菌。通过Bliss法计算得到LM10403sΔtatD口服感染小鼠的LD50为8.11×107 CFU,LM10403s的LD50为1.23×107 CFU,LM10403sCΔtatD的LD50为1.94×107 CFU。表明单核细胞增生李斯特氏菌敲除tatD基因后毒力下降。
表 1 不同菌株的毒力测定
Table 1. Strain virulence determination of bacterial strain
处理 接种剂
量/CFU死亡数/
只半数致死
量/CFU4.61×109 8 4.61×108 7 LM10403sΔtatD 4.61×107 5 8.11×107 4.61×106 2 4.61×105 1 2.80×109 9 2.80×108 6 LM10403sCΔtatD 2.80×107 5 1.94×107 2.80×106 3 2.80×105 3 4.45×109 8 LM10403s 4.45×108 6 4.45×107 6 1.23×107 4.45×106 5 4.45×105 3 PBS 0 说明:每个稀释度10只小鼠。 -
LM10403sΔtatD经灌胃第2次免疫7 d后,将LM10403s调整为1.00×1010 CFU对小鼠进行攻毒。结果显示:未免疫的LM10403s攻毒组小鼠于攻毒后全部死亡,无菌生理盐水对照组小鼠未发生死亡。而免疫LM10403sΔtatD的接种组共2只小鼠死亡,死亡时间分别为攻毒感染后的第6天和第9天,其余存活小鼠的精神状态良好,免疫保护率为80%。表明单核细胞增生性李斯特氏菌tatD基因缺失菌株能够对亲本菌株感染小鼠产生较好的免疫效果。
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对质控得到的优质序列,按照97%的相似度进行OTU分类,采用维恩图对4个处理组OTU分布情况进行分析。PBS、LM10403s、LM10403sΔtatD和LM10403sCΔtatD 4个处理独有的OTU分别为1 703、755、1 057和597个,4组共有1 781个OTU。肠道菌群多样性由高到低依次为PBS、LM10403sΔtatD、LM10403s、LM10403sCΔtatD处理组(图1)。表明tatD基因缺失后使得单核细胞增生性李斯特氏菌感染小鼠后肠道菌群多样性增加。
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从图2可见:4个处理样品的Shannon指数和Simpson指数差异不显著。Chao1和Observed species指数显示:PBS与LM10403sΔtatD处理组差异不显著,但LM10403s和LM10403sCΔtatD处理组相比于PBS处理组显著下降(P<0.05)。表明各处理小鼠肠道菌群物种均匀度相差不大,但亲本菌株感染小鼠时肠道菌群丰富度显著降低。
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Beta多样性包括多种分析方法,其中非度量多维尺度分析(NMDS)能更好地反映生态学数据的非线性结构,相同颜色为相同分组,同一组的样本距离越近,并与其他组有明显距离,说明分组效果好。图3显示:PBS与各处理组样本距离较远,LM10403sΔtatD与LM10403s、LM10403sCΔtatD处理组距离相对远,LM10403s和LM10403sCΔtatD处理组样本的聚集相近。表明LM10403sΔtatD与LM10403s、LM10403sCΔtatD处理组群落存在差异,但差异不大。
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在门水平上,使用平均丰度前50位的门丰度数据绘制热图。结果显示:优势菌门为厚壁菌门Firmicutes、变形菌门Proteobacteria、放线菌门Actinobacteria、梭杆菌门Fusobacteria和拟杆菌门Bacteroidetes。LM10403sΔtatD处理组的厚壁菌门丰度明显高于LM10403s和LM10403sCΔtatD处理组,拟杆菌门明显低于LM10403s和LM10403sCΔtatD处理组(图4)。表明单核细胞增生性李斯特氏菌tatD基因缺失后,厚壁菌门明显增加,且与PBS处理组结果相似。
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在属水平上,LM10403s、LM10403sΔtatD和LM10403sCΔtatD处理组要由乳杆菌属Lactobacillus、拟杆菌属Bacteroides和肠杆菌属Enterorhabdus组成。LM10403sΔtatD处理组的乳杆菌属相对丰度明显高于LM10403s和LM10403sCΔtatD处理组(图5)。表明tatD基因缺失使单核细胞增生性李斯特氏菌感染的小鼠肠道菌群中乳杆菌属增加。
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为进一步分析tatD基因缺失后小鼠肠道菌群改变引起的信号通路富集的差异,采用PICRUSt软件结合KEGG,分析4组小鼠在遗传信息处理、生物体系统、新陈代谢、疾病、细胞过程和环境信息处理信号通路富集的差异。结果显示:LM10403sΔtatD和PBS处理组6类生物代谢通路相关性较低,而LM10403s处理组具有较高的相关性(图6)。表明tatD基因缺失可能在单核细胞增生性李斯特氏菌感染小鼠肠道时,影响其细胞过程、新陈代谢等方面。
Effect of tatD gene deletion of Listeria monocytogenes on virulence and gut microflora in mice
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摘要:
目的 探究单核细胞增生性李斯特氏菌Listeria monocytogenes tatD基因缺失对小鼠Mus musculus毒力和肠道菌群的影响,为tatD在单核细胞增生性李斯特氏菌与宿主互作中的作用及减毒疫苗研究提供参考。 方法 采用Bliss法将亲本菌株(LM10403s)、缺失菌株(LM10403sΔtatD)和互补菌株(LM10403sCΔtatD)口服感染小鼠,确定菌株对小鼠的半数致死量(LD50)。LM10403sΔtatD以1.00×105 CFU口服免疫小鼠观察其免疫保护效果。将40只6周龄雌鼠随机平均分为对照即磷酸缓冲盐溶液组(PBS)、LM10403s组、LM10403sΔtatD组和LM10403sCΔtatD组,PBS组小鼠灌胃200 μL无菌PBS,实验组分别灌胃200 μL含1.00×106 CFU的菌液。灌胃24 h后剖杀各组小鼠,收集肠道内容物,采用Illumina Hiseq测序技术测定各处理小鼠盲肠样品微生物16S rRNA V3~V4区序列,并比较分析其微生物群落结构、多样性和信号通路富集。 结果 LM10403sΔtatD的LD50为8.11×107 CFU,毒力低于LM10403s。同时LM10403sΔtatD口服免疫小鼠后对单核细胞增生性李斯特氏菌亲本菌株的攻毒能提供80%保护率。Chao1和Observed species指数显示:PBS与LM10403sΔtatD处理组差异不显著,但LM10403s组和LM10403sCΔtatD处理组相比于PBS处理组显著下降(P<0.05)。在门水平上,LM10403sΔtatD处理组的厚壁菌门Firmicutes相对丰度高于LM10403s和LM10403sCΔtatD处理组,而在属水平上,乳杆菌属Lactobacillus相对丰度高于LM10403s和LM10403sCΔtatD处理组。功能预测分析显示:LM10403s处理组在细胞过程、环境信息处理和新陈代谢等信号通路的富集程度高于LM10403sΔtatD处理组。 结论 tatD基因缺失后单核细胞增生性李斯特氏菌的毒力降低,并具有一定的免疫保护效果。tatD基因缺失菌株感染小鼠对肠道菌群失调影响减小,且有益菌增多。图6表1参21 -
关键词:
- tatD基因 /
- 单核细胞增生性李斯特氏菌 /
- 毒力 /
- 16S rRNA /
- 肠道菌群
Abstract:Objective This study, with an investigation of the effects of tatD gene deletion in Listeria monocytogenes on virulence and gut microbiota in mice (Mus musculus), is aimed to provide reference for the role of tatD in the interaction between L. monocytogenes and the host, as well as for the study of attenuated vaccines. Method First, mice were orally infected with LM10403s, LM10403sΔtatD and LM10403sCΔtatD strains using the Bliss method to determine the strain’s median lethal dose (LD50) for mice before immunoprotective effect of LM10403sΔtatD was observed in mice immunized with 1.00×105 CFU orally. Then, forty 6-week-old female mice were randomly and equally divided into PBS (ck), LM10403s, LM10403sΔtatD, and LM10403sCΔtatD groups, with those in the ck group gavaged with 200 μL of sterile PBS and the ones in the experimental group gavaged with 200 μL of bacterial solution containing 1.00 × 106 CFU, respectively. Next, after 24 h of gavage, the mice in each group were dissected and killed, with intestinal contents collected before Illumina Hiseq sequencing technology was used to determine the sequences of the microbial 16S rRNA V3−V4 regions of the cecum samples from each group so that a comparative analysis was conducted of the structure of microbial communities, diversity, and signaling pathway enrichment. Result The LD50 of LM10403sΔtatD was 8.11×107 CFU, which was less virulent than that of the parental strain. Oral immunization of mice with LM10403sΔtatD provided 80% protection against L. monocytogenes parental strain infection. Chao1 and Observed species indices showed that the difference between ck and LM10403sΔtatD group was not significant, but LM10403s and LM10403sCΔtatD group were significantly lower compared to ck group (P<0.05). At the phylum level, the relative abundance of the Firmicutes in LM10403sΔtatD group was higher than that in LM10403s and LM10403sCΔtatD group, and at the genus level, the relative abundance of the genus, Lactobacillus in LM10403sΔtatD group was higher than that in LM10403s and LM10403sCΔtatD group functional prediction analysis showed that LM10403s group in signaling pathways including cellular processes, environmental information processing, and metabolism was more enriched than the LM10403sΔtatD group. Conclusion The deletion of tatD gene reduced the virulence of L. monocytogenes and had animmuno protective effects while infection of the tatD gene deletion mutant strain in mice reduced the effect on intestinal flora dysbiosis and increased the beneficial bacteria. [Ch, 6 fig. 1 tab. 21 ref.] -
Key words:
- tatD gene /
- Listeria monocytogenes /
- virulence /
- 16S rRNA /
- gut microbiota
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表 1 不同菌株的毒力测定
Table 1. Strain virulence determination of bacterial strain
处理 接种剂
量/CFU死亡数/
只半数致死
量/CFU4.61×109 8 4.61×108 7 LM10403sΔtatD 4.61×107 5 8.11×107 4.61×106 2 4.61×105 1 2.80×109 9 2.80×108 6 LM10403sCΔtatD 2.80×107 5 1.94×107 2.80×106 3 2.80×105 3 4.45×109 8 LM10403s 4.45×108 6 4.45×107 6 1.23×107 4.45×106 5 4.45×105 3 PBS 0 说明:每个稀释度10只小鼠。 -
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https://zlxb.zafu.edu.cn/article/doi/10.11833/j.issn.2095-0756.20220758