人轮状病毒感染昆明小鼠乳鼠模型的建立

目的建立人轮状病毒G3型709株感染4d龄昆明小鼠乳鼠模型。方法通过灌胃病毒的方式造模,观察乳鼠被病毒攻击后不同时间其临床表现、小肠组织病理改变、小肠组织上皮细胞超微结构改变。酶联免疫吸附法检测轮状病毒抗原在乳鼠粪便中的表达,免疫荧光法检测轮状病毒在乳鼠小肠组织中的表达。结果4d龄昆明小鼠乳鼠被轮状病毒攻击24h后出现腹泻表现和小肠组织病理改变,72h最严重,之后腹泻率下降,病理改变减轻,第7天腹泻停止,病理改变消失。乳鼠小肠上皮细胞出现糖、脂肪代谢紊乱,其粪便和小肠组织中都可以检测出轮状病毒抗原表达。结论4d龄昆明小鼠乳鼠被人轮状病毒A组G3型709株经口攻击后病毒能够在其体内复制,出现腹泻表现。该病毒感染腹泻过程具有自愈特点。     

不同剂型七味白术散对肠道菌群失调小鼠小肠黏膜超微结构和sIgA的影响

目的探讨七味白术散、七味白术滴剂和七味白术提取物对抗生素联合番泻叶致菌群失调小鼠小肠黏膜超微结构和sIgA的影响。方法小鼠经头孢曲松钠和盐酸林可霉素加冰番泻叶灌胃造成菌群失调模型。将小鼠分为正常组、模型组(造模成功后即为自然恢复组)、七味白术散煎剂组、七味白术散滴剂组和七味白术散提取物组。治疗后,进行小鼠肠组织超微结构观察,小肠黏膜组织sIgA含量和黏膜上皮细胞内sIgA的表达检测。结果小肠超微结构显示,不同剂型七味白术散组均能明显改善模型动物小肠黏膜炎症病变和促进小肠肠道sIgA的增加。结论七味白术散能有效提高小肠肠道sIgA含量,修复损伤小肠黏膜免疫组织,减轻菌群失调腹泻。     

小鼠肠道菌群失调与调整的实验观察

本文定量检测４０只小鼠新鲜大便中的优势菌群。依次为类杆菌、乳杆菌、大肠杆菌和肠球菌。作者用抗生素抑制小鼠肠道正常菌群,再以鼠伤寒沙门氏菌感染这些小鼠,加重了肠道菌群失调,小鼠失去定值抗力。然后将鼠粪制剂,丽珠肠乐进行分组调整,并以抗生素 伤寒沙门氏菌不治疗作阴性对照组;肉汤＋鼠伤寒沙门氏菌不治疗作对照组,连续观察一周。     

鸡产蛋下降综合征病毒NE4毒株对KM小鼠感染特性观察

目的初步探究鸡产蛋下降综合征病毒NE4（EDSV NE4）毒株对昆明小鼠的感染特性。方法用106TCID50攻毒量的EDSV NE4株对4～6周龄的KM小鼠进行攻毒试验,同时以正常尿囊液接种作为阴性对照。用荧光定量PCR对小鼠组织及粪便中的EDSV进行检测,同时用HE染色及免疫组化法对小鼠组织切片进行病理组织学观察和抗原定位。结果 EDSV攻毒对小鼠的采食情况产生一定影响,但并未引起明显的临床症状;攻毒组小鼠可产生针对EDSV特异性的抗体,HI抗体滴度可高达212,阴性对照组小鼠体内抗体检测为阴性;攻毒后小鼠大部分组织器官如肝脏、子宫、肾脏、肺脏等与攻毒7 d后粪便中均可检测到EDSV,阴性对照小鼠所有受检组织中均未检测到病毒;EDSV攻毒未能引起小鼠组织的病理学变化,攻毒后不同时间内,可在子宫、肺脏、肝脏、肾脏中可检测到阳性信号,最为典型的定殖位置是子宫腺体上皮细胞及肌层细胞的胞质中。结论 EDSV NE4株可以感染KM小鼠。     

重组狂犬病病毒糖蛋白活酵母疫苗经小鼠口服给药后的免疫效果

目的:研究以活酵母为输送载体的狂犬病疫苗对小鼠的免疫保护能力和免疫疗程。方法:小鼠首先灌食高浓度空白活酵母INVSI,并于灌胃后8h和12h分别采集小鼠空肠和回肠组织并提取小肠浸出液培养,计算活酵母经肠胃环境后的存活率;分别取狂犬病糖蛋白(glycoprotein,G)分泌型表达菌株pYes-InG和胞内表达型菌株pYes-G灌胃小鼠,灌胃结束后12h采集小鼠血清和小肠组织,采用免疫组织化学方法检测抗原物质G在小肠上皮细胞的分布,采用ELISA检测小鼠血清中和性抗体的滴度。结果:活酵母经灌食消化8h后在小肠中的存活率最高达36.11%,12h后降至0.59%;口服分泌型pYes-InG重组酵母的小鼠小肠组织和血清中能检测到抗原物质G和低量的中和性抗体,ELISA分析显示,小鼠经过3~4次免疫接种,免疫效果基本恒定,而口服胞内表达型pYes-G重组酵母的小鼠小肠组织和血清中均未检测到目标物。结论:分泌型重组酵母pYes-InG经多次口服可对狂犬病起到一定的预防作用,但它诱导产生的中和性抗体浓度低,免疫应答慢,虽不适合用于控制突发性狂犬病的传染以及治疗狂犬病患者,但从免疫机制、免疫方式、安全性以及生产成本等因素考虑,仍具有良好的研究价值。     

用体内激活的启动子调控HCV核心抗原表达可增强重组鼠伤寒沙门氏菌的免疫原性

为提高抗原表达质粒在重组伤寒沙门氏菌中的稳定性以增强重组伤寒沙门氏菌诱导的免疫应答 ,克隆鼠伤寒沙门氏菌pagC基因启动子 ,以其为转录调控元件构建HCV核心抗原表达质粒 ,转化到减毒鼠伤寒沙门氏菌中。体外培养时 ,Mg2 能够剂量依赖性抑制该重组菌表达HCV核心抗原。将该重组菌和组成性表达的重组菌分别口服接种BALB/c小鼠 ,观察质粒的稳定性和小鼠的免疫应答。结果表明 ,体内激活的pagC基因启动子能明显提高质粒在重组鼠伤寒沙门氏菌中的稳定性和增强重组菌诱导的体液和细胞免疫应答 ,这为发展高效免疫、成本低廉的口服丙肝疫苗提供了一个新思路     

减蛋综合征病毒在不同品系小鼠体内的组织分布

目的通过人工感染减蛋综合征病毒(egg drop syndrome virus,EDSV),观察病毒在不同品系小鼠体内增殖情况以及动态变化规律,为EDSV构建载体提供理论依据与数据支持。方法选取免疫系统正常的BALB/c小鼠、T细胞免疫缺陷裸鼠(Nu)以及高度免疫缺陷小鼠(NSG)为研究对象,每品系32只,雌性,5～6周龄,经腹腔注射人工感染EDSV,分别于攻毒后1、3、5、7、14、21、28、35 d采集血清,应用间接ELISA方法进行抗体监测;选择攻毒后1、7、14、21、28 d小鼠,采集心脏、肺、肝、脾、肾、小肠、子宫、气管、食管、脑10种组织,应用荧光定量PCR相对定量比较Ct法(△△CT)进行各组织内病毒载量的检测。结果 BALB/c小鼠于攻毒后3 d即可在血清内检测到抗体的表达,14 d抗体水平达到最高,并一直维持至监测期内35 d;Nu小鼠也可于攻毒后3 d检测到抗体,表达水平较BALB/c小鼠有所降低,攻毒14 d后,Nu小鼠血清中抗体水平出现下降,至35 d抗体一直维持在较低的水平;NSG小鼠在整个监测过程中,抗体水平一直处于阴性状态。核酸相对定量结果显示,BALB/c小鼠感染后1 d,肝组织中的病毒表达量最高,达到5.45个数量级,其次由高到低依次是脾、食管、子宫、小肠、肺、气管、肾、心脏,脑组织中病毒含量最低,随感染时间的延长,各组织内病毒表达量较感染1 d均有所下降,至攻毒后28 d,肝、脾病毒表达量依然维持着较高的水平;Nu小鼠和NSG小鼠感染1 d表现为脾中病毒表达量最高,分别为3.95和4.05个数量级,其次为肝,攻毒28 d,两种小鼠体内各器官内仍可以检出阳性信号,肝、脾病毒表达量较高。结论 EDSV可刺激小鼠产生免疫应答,在免疫缺陷小鼠体内抗体水平表达量较低。该病毒在小鼠体内有肝、脾等组织嗜性,为EDSV开发成为载体以及在实验动物模型上的进一步研究与应用提供了参考数据。     

ICAM-1及其受体在高致病性禽流感病毒性肺炎中的作用研究

本文应用高致病性禽流感病毒性肺炎(Highlypathogenicavianinfluenzaviralpneumonia,HPAIVP)小鼠模型,采用免疫组织化学染色方法,对实验组和对照组小鼠肺组织中ICAM-1及其受体的表达含量进行检测。研究发现:实验组小鼠肺组织中ICAM-1及其受体表达含量在攻毒后1d即开始升高,第4天达高峰。就攻毒剂量来说,以100LD50/50μL攻毒组小鼠肺组织中ICAM-1及其受体阳性表达量升高最明显。并通过ELASA方法进一步证实了这种变化。结果表明:ICAM-1及其受体在HPAIVP中呈现高表达,可能在其发病中发挥了重要作用。     

两种肠道侵袭性菌与小鼠小肠微皱褶细胞相互作用的初步研究

利用小鼠肠袢模型进行局部感染,在不同的时间取Peyer's结对其进行扫描电镜和透射电镜的观察,并用流式细胞仪检测细胞凋亡。结果表明,鼠伤寒沙门低菌460043和痢疾杆菌F2a-12两种肠道侵袭性菌与微皱褶细胞的粘附发生在局部感染30min,感染60－90min在M细胞和淋巴细胞中可见到细菌,而在感染6－8h后Peyer's结中的细胞凋亡百分率与对照相比差异最为明显。提示：鼠伤寒沙门氏菌460043和痢疾杆菌F2a-12均是借助于M细胞通过上皮屏障,从而引起局部的粘膜反应。     

发热伴血小板减少综合征病毒感染Balb/C小鼠和金黄地鼠的免疫病理反应

发热伴血小板减少综合征病毒(Severe fever with thrombocytopenia syndrome irus,SFTSV)是新发传染病发热伴血小板减少综合征的致病病原,为布尼亚病毒科白蛉病毒属的一种新型病毒。为了分析SFTSV感染Balb/C小鼠和金黄地鼠引起的免疫病理反应,本研究采用两个攻毒剂量组分为高剂量组(105 TCID50),低剂量组(103TCID50),以及溶剂对照组,并采用经静脉、肌肉、脑、和腹腔4种途径分别进行攻毒。在攻毒后不同时间点取血样,应用全自动血细胞计数仪检测血细胞亚群,Real-time PCR实验检测血液中病毒RNA拷贝数,悬浮芯片实验检测血浆中IgG和IgM抗体水平。在攻毒后第14d处死动物,收集心、肝、脾、肺、肾、小肠、肌肉和脑8种组织器官进行HE染色,观察组织病理改变。研究结果显示,SFTSV可感染Balb/C小鼠和金黄地鼠,在攻毒后第7d检测到病毒特异性IgM和IgG,其中IgM在第7d达到峰值后下降,IgG在攻毒后第14d达到峰值。组织病理学分析显示病毒感染Balb/C小鼠和金黄地鼠的肝组织和肾组织出现明显病变。本研究揭示SFTSV可以感染不同品系的啮齿类动物,引起相似的免疫抗体反应和组织病理变化。     

MyD88 signaling promotes both mucosal homeostatic and fibrotic responses during Salmonella-induced colitis

Salmonella enterica serovar Typhimurium is a clinically important gram-negative, enteric bacterial pathogen that activates several Toll-like receptors (TLRs). While TLR signaling through the adaptor protein MyD88 has been shown to promote inflammation and host defense against the systemic spread of S. Typhimurium, curiously, its role in the host response against S. Typhimurium within the mammalian gastrointestinal (GI) tract is less clear. We therefore used the recently described Salmonella-induced enterocolitis and fibrosis model: wild-type (WT) and MyD88-deficient (MyD88(-/-)) mice pretreated with streptomycin and then orally infected with the ΔaroA vaccine strain of S. Typhimurium. Tissues were analyzed for bacterial colonization, inflammation, and epithelial damage, while fibrosis was assessed by collagen quantification and Masson's trichrome staining. WT and MyD88(-/-) mice carried similar intestinal pathogen burdens to postinfection day 21. Infection of WT mice led to acute mucosal and submucosal inflammation and edema, as well as significant intestinal epithelial damage and proliferation, leading to widespread goblet cell depletion. Impressive collagen deposition in the WT intestine was also evident in the submucosa at postinfection days 7 and 21, with fibrotic regions rich in fibroblasts and collagen. While infected MyD88(-/-) mice showed levels of submucosal inflammation and edema similar to WT mice, they were impaired in the development of mucosal inflammation, along with infection-induced epithelial damage, proliferation, and goblet cell depletion. MyD88(-/-) mouse tissues also had fewer submucosal fibroblasts and 60% less collagen. We noted that cyclooxygenase (Cox)-2 expression was MyD88-dependent, with numerous Cox-2-positive cells identified in fibrotic regions of WT mice at postinfection day 7, but not in MyD88(-/-) mice. Treatment of WT mice with the Cox-2 inhibitor rofecoxib (20 mg/kg) significantly reduced fibroblast numbers and collagen levels without altering colitis severity. In conclusion, MyD88 and Cox-2 signaling play roles in intestinal fibrosis during Salmonella-induced enterocolitis.     

IL-17A/F-signaling does not contribute to the initial phase of mucosal inflammation triggered by S. Typhimurium

Salmonella enterica subspecies 1 serovar Typhimurium (S. Typhimurium) causes diarrhea and acute inflammation of the intestinal mucosa. The pro-inflammatory cytokines IL-17A and IL-17F are strongly induced in the infected mucosa but their contribution in driving the tissue inflammation is not understood. We have used the streptomycin mouse model to analyze the role of IL-17A and IL-17F and their cognate receptor IL-17RA in S. Typhimurium enterocolitis. Neutralization of IL-17A and IL-17F did not affect mucosal inflammation triggered by infection or spread of S. Typhimurium to systemic sites by 48 h p.i. Similarly, Il17ra(-/-) mice did not display any reduction in infection or inflammation by 12 h p.i. The same results were obtained using S. Typhimurium variants infecting via the TTSS1 type III secretion system, the TTSS1 effector SipA or the TTSS1 effector SopE. Moreover, the expression pattern of 45 genes encoding chemokines/cytokines (including CXCL1, CXCL2, IL-17A, IL-17F, IL-1α, IL-1β, IFNγ, CXCL-10, CXCL-9, IL-6, CCL3, CCL4) and antibacterial molecules was not affected by Il17ra deficiency by 12 h p.i. Thus, in spite of the strong increase in Il17a/Il17f mRNA in the infected mucosa, IL-17RA signaling seems to be dispensable for eliciting the acute disease. Future work will have to address whether this is attributable to redundancy in the cytokine signaling network.     

Caloric restriction increases free radicals and inducible nitric oxide synthase expression in mice infected with Salmonella Typhimurium

It is well known that CR (caloric restriction) reduces oxidative damage to proteins, lipids and DNA, although the underlying mechanism is unclear. However, information concerning the effect of CR on the host response to infection is sparse. In this study, 6-month-old mice that were fed AL (ad libitum) or with a CR diet were infected with Salmonella serovar Typhimurium. EPR (electron paramagnetic resonance; also known as ESR (electron spin resonance)) was used to identify FRs (free radicals). These results were subsequently correlated with SOD (superoxide dismutase) catalytic activity, iNOS [inducible NOS (nitric oxide synthase) or NOSII] expression and NO (nitric oxide) content. EPR analysis of liver samples demonstrated that there was a higher quantity of FRs and iron-nitrosyl complex in infected mice provided with a CR diet as compared with those on an AL diet, indicating that CR was beneficial by increasing the host response to Salmonella Typhimurium. Furthermore, in infected mice on the CR diet, NOSII expression was higher, NO content was greater and spleen colonization was lower, compared with mice on the AL diet. No changes in SOD activity were detected, indicating that the NO produced participated more in the formation of iron-nitrosyl complexes than peroxynitrite. These results suggest that CR exerts a protective effect against Salmonella Typhimurium infection by increasing NO production.     

Inhibition of tissue inflammation and bacterial translocation as one of the protective mechanisms of Saccharomyces boulardii against Salmonella infection in mice

Growing evidences suggest that Saccharomyces boulardii (SB) is efficacious against bacterial infections and inflammatory bowel diseases. This study investigated the effects of treatment with SB provided in a murine model of typhoid fever. Mice were divided into two groups: (1) control animals challenged with Salmonella Typhimurium (ST), and (2) animals receiving SB, and then challenged with ST. At days 0, 1, 5, 10 and 15 post-challenge, animals were euthanized and tissues collected to analyze bacterial translocation, cytokines, signaling pathways and histological analysis. Survival rate and animal weight were also evaluated. Treatment with SB increased survival rate and inhibited translocation of bacteria after ST challenge. Histological data showed that SB also protected mice against liver damage induced by ST. SB decreased levels of inflammatory cytokines and activation of mitogen-activated protein kinases (p38, JNK and ERK1/2), phospho-IκB, p65-RelA, phospho-jun and c-fos in the colon, signal pathways involved in the activation of inflammation induced by ST. Further experiments revealed that probiotic effects were due, at least in part, to the binding of ST to the yeast. Such binding diminishes ST translocation, resulting in decreased activation of signaling pathways which lead to intestinal inflammation in a murine model of typhoid fever.     

Salmonella type III effector SpvC, a phosphothreonine lyase, contributes to reduction in inflammatory response during intestinal phase of infection

Salmonella phosphothreonine lyase SpvC inactivates the dual-phosphorylated host mitogen-activated protein kinases (MAPK) through β-elimination. While SpvC can be secreted in vitro by both Salmonella pathogenicity island (SPI)-1 and SPI-2 type III secretion systems (T3SSs), translocation of this protein into the host cell cytosol has only been demonstrated by SPI-2 T3SS. In this study, we show that SpvC can be delivered into the host cell cytoplasm by both SPI-1 and SPI-2 T3SSs. Dephosphorylation of the extracellular signal-regulated protein kinases (ERK) was detected in an SPI-1 T3SS-dependent manner 2 h post infection. Using a mouse model for Salmonella enterocolitis, which was treated with streptomycin prior to infection, we observed that mice infected with Salmonella enterica serovar Typhimurium strains lacking the spvC gene showed pronounced colitis when compared with mice infected with the wild-type strain 1 day after infection. The effect of SpvC on the development of colitis was characterized by reduced mRNA levels of the pro-inflammatory cytokines and chemokines, and reduced inflammation with less infiltration of neutrophils. Furthermore, the reduction in inflammation by SpvC resulted in increased bacterial dissemination in spleen of mice infected with Salmonella. Collectively, our findings suggest that SpvC exerts as an anti-inflammatory effector and the attenuation of intestinal inflammatory response by SpvC is involved in systemic infection of Salmonella.     

Salmonella Typhimurium SPI-1 genes promote intestinal but not tonsillar colonization in pigs

Salmonella Pathogenicity Island 1 (SPI-1) genes are indispensable for virulence of Salmonella Typhimurium in several animal species. The role of SPI-1 in the pathogenesis of Salmonella Typhimurium infections of pigs, however, is not well described. The interactions of a porcine Salmonella Typhimurium field strain and its isogenic mutants with disruptions in the SPI-1 genes hilA, sipA and sipB with porcine intestinal epithelial cells were characterized in vitro and in a ligated intestinal loop model in pigs. HilA and SipB were essential in the invasion of porcine intestinal epithelial cells in vitro. A sipA mutant was impaired for invasion using a polarized cell line, but fully invasive in a non-polarized cell line. All SPI-1 mutants induced a significant decrease in influx of neutrophils in the porcine intestinal loop model compared with the wild type strain. Pigs were orally inoculated with 10(8) colony forming units of both the wild type Salmonella Typhimurium strain and its isogenic sipB::kan mutant strain. The sipB mutant strain was significantly impaired to invade the intestinal, but not the tonsillar tissue, one day after inoculation and was unable to efficiently colonize the intestines and the GALT, but not the tonsils, 3 days after inoculation. This study shows that SPI-1 plays a crucial role in the invasion and colonization of the porcine gut and in the induction of influx of neutrophils towards the intestinal lumen, but not in the colonization of the tonsils.     

Evaluation of methods for the identification of Salmonella enterica serotype Typhimurium DT104 from poultry environmental samples

An increase in the prevalence of Salmonella enterica serotype Typhimurium DT104 has been reported worldwide. This study examined the prevalence of this microorganism in poultry environmental samples from commercial layer flocks and pullet environments as well as the sensitivity and specificity of a PCR-based method, and multiple antibiotic resistance profile of Salmonella serogroup B isolates in relation to the serotype and phagetype reference method for the identification of Salmonella Typhimurium DT104. A total of 435 Salmonella isolates were obtained from poultry house environmental samples tested during a 20-month period representing a prevalence of 5.5%. Of these, 313 (72%) isolates were identified as Salmonella serogroup B isolates. These isolates were tested by a PCR-based assay, and for resistance to five antibiotics: ampicillin, chloramphenicol, streptomycin, sulfonamides, and tetracycline (ACSSuT) for the rapid identification of Salmonella Typhimurium DT104. Upon comparing the antibiotic resistance and PCR results with serotype and phage type data, the sensitivity and specificity for the identification of Salmonella Typhimurium DT104 of both methods were found to be 100%, and 99.6%, respectively. Both methods can be completed within 24 h after obtaining an isolate, while serotyping and phagetyping required more than 5 days to complete.     

The intestinal microbiota plays a role in Salmonella-induced colitis independent of pathogen colonization

The intestinal microbiota is composed of hundreds of species of bacteria, fungi and protozoa and is critical for numerous biological processes, such as nutrient acquisition, vitamin production, and colonization resistance against bacterial pathogens. We studied the role of the intestinal microbiota on host resistance to Salmonella enterica serovar Typhimurium-induced colitis. Using multiple antibiotic treatments in 129S1/SvImJ mice, we showed that disruption of the intestinal microbiota alters host susceptibility to infection. Although all antibiotic treatments caused similar increases in pathogen colonization, the development of enterocolitis was seen only when streptomycin or vancomycin was used; no significant pathology was observed with the use of metronidazole. Interestingly, metronidazole-treated and infected C57BL/6 mice developed severe pathology. We hypothesized that the intestinal microbiota confers resistance to infectious colitis without affecting the ability of S. Typhimurium to colonize the intestine. Indeed, different antibiotic treatments caused distinct shifts in the intestinal microbiota prior to infection. Through fluorescence in situ hybridization, terminal restriction fragment length polymorphism, and real-time PCR, we showed that there is a strong correlation between the intestinal microbiota composition before infection and susceptibility to Salmonella-induced colitis. Members of the Bacteroidetes phylum were present at significantly higher levels in mice resistant to colitis. Further analysis revealed that Porphyromonadaceae levels were also increased in these mice. Conversely, there was a positive correlation between the abundance of Lactobacillus sp. and predisposition to colitis. Our data suggests that different members of the microbiota might be associated with S. Typhimurium colonization and colitis. Dissecting the mechanisms involved in resistance to infection and inflammation will be critical for the development of therapeutic and preventative measures against enteric pathogens.     

Increased resistance of mice to Salmonella enterica serovar Typhimurium infection by synbiotic administration of Bifidobacteria and transgalactosylated oligosaccharides

AIMS: The anti-infectious activity of Bifidobacteria in combination with transgalactosylated oligosaccharides (TOS) against Salmonella enterica serovar Typhimurium LT-2 in an opportunistic antibiotic-induced murine infection model in mice was examined. METHODS AND RESULTS: B. breve (strain Yakult) with natural resistance to streptomycin sulphate (SM, MIC: > 4 mg ml(-1)), when given daily at a dose of 108 cfu/mouse orally under SM treatment was constantly excreted at 10(10) cfu g(-1) faeces so long as SM was administered, even at 2 weeks after discontinuing administration of B. breve. Explosive intestinal growth and subsequent extra-intestinal translocation of orally infected LT-2 under SM treatment were inhibited by B. breve colonization, and this anti-infectious activity was strengthened by synbiotic administration of TOS with B. breve. Comparison of anti-Salmonella activity among several Bifidobacterium strains with natural resistance to SM revealed that strains such as B. bifidum ATCC 15696 and B. catenulatum ATCC 27539T conferred no activity, even when they reached high population levels similar those of effective strains such as strain Yakult and B. pseudocatenulatum DSM 20439. Both the increase in the concentration of organic acids and the lowered pH in the intestine due to bifidobacterial colonization correlated with the anti-infectious activity. Moreover, the crude cecal extract of B. breve-colonized mice exerted growth-inhibitory activity against LT-2 in vitro, whereas that of the ineffective B. bifidum-colonized cecum showed much lower activity. CONCLUSIONS: Intestinal colonization by bifidobacteria given exogenously together with TOS during antibiotic treatment prevents the antibiotic-induced disruption of colonization resistance to oral infection with S. enterica serovar Typhimurium, and the metabolic activity needed to produce organic acids and lower the intestinal pH is important in the anti-infectious activity of synbiotics against enteric infection with Salmonella. SIGNIFICANCE AND IMPACT OF THE STUDY: These results indicate that certain bifidobacteria together with prebiotics may be used for the prophylaxis against opportunistic intestinal infections with antibiotic-resistant pathogens.     

Antimicrobial Peptide JH-3 Effectively Kills Salmonella enterica Serovar Typhimurium Strain CVCC541 and Reduces Its Pathogenicity in Mice

Salmonella is an important zoonotic pathogen and is a major cause of gastrointestinal diseases worldwide. The current serious problem of antibiotic abuse has prompted the search for new substitutes for antibiotics. JH-3 is a small antimicrobial peptide with broad-spectrum bactericidal activity. In this study, we showed that JH-3 has good bactericidal activity towards the clinical isolate Salmonella enterica serovar Typhimurium strain CVCC541. The minimum inhibitory concentration (MIC) of JH-3 against this bacterium was determined to be 100 μg/mL, which could decrease the number of CVCC541 cells by 1000-fold in vitro within 5 h. The transmission electron microscopy (TEM) results showed that JH-3 can damage the cell wall and membrane of CVCC541, leading to the leakage of cell contents and subsequent cell death. To measure the bactericidal activity of CVCC541-infected mice were treated intraperitoneally 40 or 10 mg/kg JH-3 at 2 h or 3 days postinfection. Our results showed that treatment with 40 mg/kg JH-3 at 2 h postinfection had the best therapeutic effect and could significantly protect mice from a lethal dose of CVCC541. Furthermore, the clinical symptoms, bacterial burden in blood and organs, and intestinal pathological changes were all decreased and were close to normal. This study examined the therapeutic effect of the antimicrobial peptide JH-3 against S. enterica CVCC541 infection for the first time and determined the therapeutic effect of different JH-3 doses and treatment times, laying the foundation for studies of new antimicrobial agents.