Bacterial translocation from the intestines

Bacterial translocation is defined as the passage of viable bacteria from the gastrointestinal (GI) tract through the mucosal epithelium to other sites, such as the mesenteric lymph nodes, spleen, liver and blood. This paper reviews results from animal models utilized to obtain information concerning the defense mechanisms operating in the healthy host to confine bacteria to the GI tract. Gnotobiotic and antibiotic-decontaminated mice colonized with particular bacteria demonstrated that the indigenous GI flora maintains an ecologic equilibrium to prevent intestinal bacterial overgrowth and translocation from the GI tract. Studies with athymic (nu/nu) mice, thymus-grafted (nu/nu) mice, neonatally thymectomized mice, and mice injected with immunosuppressive agents demonstrated that the host immune system is another defense mechanism inhibiting bacterial translocation from the GI tract. Ricinoleic acid given orally to mice disrupted the intestinal epithelial barrier allowing indigenous bacteria to translocate from the GI tract. Thus, bacterial translocation from the GI tract of healthy adult mice is inhibited by: (a) an intact intestinal epithelial barrier, (b) the host immune defense system, and (c) an indigenous GI flora maintaining ecological equilibrium to prevent bacterial overgrowth. Deficiencies in host defense mechanisms act synergistically to promote bacterial translocation from the GI tract as demonstrated by animal models with multiple alterations in host defenses. Bacterial translocation occurred to a greater degree in mice with streptozotocin-induced diabetes, mice receiving nonlethal thermal injury, and mice receiving the combination of an immunosuppressive agent plus an oral antibiotic than in mice with only a primary alteration in host defenses. The study of bacterial translocation in these complex models suggests that opportunistic infections from the GI tract occur in discrete stages. In the healthy adult animal, bacterial translocation from the GI tract either does not occur or occurs at a very low level and the host immune defenses eliminate the translocating bacteria. Bacterial translocation does take place if one of the host defense mechanisms is compromised, such as a deficiency in the immune response, bacterial overgrowth in the intestines, or an increase in the permeability of the intestinal barrier. In this first stage, the bacteria usually translocate in low numbers to the mesenteric lymph node, and sometimes spleen or liver, but do not multiply and spread systemically.(ABSTRACT TRUNCATED AT 400 WORDS)     

Bacteriological Studies of the Effects of Cow's Milk on Dental Plaque and Dental Caries in Rats

The effects of liquid milk and skim milk powder on the bacterial composition of rat dental plaque and dental caries were examined in two separate experiments. First, groups of rats fed a cariogenic diet plus one or other of three types of liquid milk had. after 28 d. similar plaque flora. Those rats receiving reconstituted spray-dried skim milk had a significantly higher incidence of dental caries than those receiving either pasteurized and homogenized milk or ultra-heat treated milk. The differences in caries scores may be related to differences in inorganic phosphate and calcium levels of the milks. Secondly, rats fed a diet containing 65% phosphate-free sucrose plus 32% spray-dried skim milk in powder form had a significantly lower dental caries score than did rats receiving a diet containing 65% sucrose plus 32% autoclaved roller-dried skim milk powder. At the end of this experiment, the plaque flora had changed significantly and the difference in caries incidence was related to the reduction in the percentage of potentially cariogenic bacteria.
These results indicate that the mechanism by which milk reduces dental caries incidence may be (a) by remineralizing incipient carious lesions or (b) by mediating changes in the bacterial composition of dental plaque.     

Effects of laxative and N-acetylcysteine on mucus accumulation, bacterial load, transit, and inflammation in the cystic fibrosis mouse small intestine

The accumulation of mucus in affected organs is characteristic of cystic fibrosis (CF). The CF mouse small intestine has dramatic mucus accumulation and exhibits slower interdigestive intestinal transit. These factors are proposed to play cooperative roles that foster small intestinal bacterial overgrowth (SIBO) and contribute to the innate immune response of the CF intestine. It was hypothesized that decreasing the mucus accumulation would reduce SIBO and might improve other aspects of the CF intestinal phenotype. To test this, solid chow-fed CF mice were treated with an osmotic laxative to improve gut hydration or liquid-fed mice were treated orally with N-acetylcysteine (NAC) to break mucin disulfide bonds. Treatment with laxative or NAC reduced mucus accumulation by 43% and 50%, respectively, as measured histologically as dilation of the intestinal crypts. Laxative and NAC also reduced bacterial overgrowth in the CF intestine by 92% and 63%, respectively. Treatment with laxative normalized small intestinal transit in CF mice, whereas NAC did not. The expression of innate immune response-related genes was significantly reduced in laxative-treated CF mice, whereas there was no significant effect in NAC-treated CF mice. In summary, laxative and NAC treatments of CF mice reduced mucus accumulation to a similar extent, but laxative was more effective than NAC at reducing bacterial load. Eradication of bacterial overgrowth by laxative treatment was associated with normalized intestinal transit and a reduction in the innate immune response. These results suggest that both mucus accumulation and slowed interdigestive small intestinal transit contribute to SIBO in the CF intestine.     

Effects of dietary antibiotics on intestinal microflora in broiler chickens

Changes were examined in the intestinal microflora in broiler chickens fed a diet containing antibiotics to obtain fundamental information on the mechanisms of beneficial effect of the antibiotics upon livestock production. Three antibiotics (colistin, bacitracin, and enramycin) were employed as feed additives. Experiments were conducted with broiler chickens in two ways. In one way dietary antibiotics were fed continually at levels approved for use as feed additives for a long term. In the other they were fed the same antibiotics for a short term. Significant changes in microflora were observed mainly in such bacterial groups as aerobic bacteria and Lactobacillus. In the long term administration, three possible modes of variance in the bacterial flora were postulated: Changes directly related to the antibacterial spectrum of antibiotics. Antagonistic changes related to an ecological balance in the bacterial flora. Changes in quantitative balance of bacteria constituting each bacterial group. The change in the intestinal microflora during administration of the antibiotic diet was expressed as a complex form of these transition modes. In the short term administration, it was demonstrated that the effect of the antibiotic diet lingered even 7 days after administration. This suggests that antibiotics used as feed additives may possibly affect the stability of the intestinal microflora.     

Effect of fish-fat or beef-fat supplemented diet on immune complex-induced enteropathy in the rat

In contrast to animals on a beef fat-supplemented diet (BFD), animals maintained on a fish fat-supplemented diet (FFD) incorporate increased amounts of eicosapentaenoic acid (EPA) into membrane phospholipids. Generation of lipid mediators from such tissues favors the formation of compounds with less pro-inflammatory activity than are derived from tissues poor in EPA. Nevertheless, the FFD has not had a uniformly beneficial effect on animal models of inflammatory diseases. We previously showed that intravenous injection of rat anti-BSA-BSA complexes (IC) prepared in 5x antigen excess rapidly induced a striate pattern of serosal (to mucosal) hemorrhage and vascular congestion throughout the small intestine. In this study, we tested the effect of a BFD and FFD on immune complex-induced enteropathy. After six (Expt. 1) or eight weeks (Expt. 2) on the diet, rats were injected with IC and the severity of serosal hyperemia in the small intestine was scored. In some FFD, no lesions were seen under conditions which elicited moderate to severe lesions in BFD rats. In Expt. 1 involving 22 rats and in Expt. 2 involving 28 rats, those on the FFD had a significantly lower composite lesional score compared to those on the BFD, p less than 0.005 and p less than 0.005, respectively. These results indicate that the FFD had a beneficial effect on IC-induced enteropathy. It is suggested that this effect of the FFD may be mediated primarily by a reduction in availability of platelet-activating factor.     

Experimental cholelithiasis in the rabbit induced by cholestanol feeding: effect of neomycin treatment on bile composition and gallstone formation

Fed cholestanol is converted by the rabbit to 5alpha-bile acids which coprecipitate with the normally occurring 5beta-bile acids to form gallstones composed of calcium and sodium glycoallodeoxycholate and glycodeoxycholate. The present study shows that oral administration of large doses of neomycin prevents gallstone formation in the cholestanol-fed rabbit and reduces the elevated concentration of allodeoxycholic acid in bile, with a reciprocal increase in allocholic acid concentration. The reduction in the concentration of allodeoxycholic acid and in the incidence of gallstones is proportional to the dose of neomycin; at a concentration of allodeoxycholic acid below about 20% of total bile acids, gallstone formation does not occur. Neomycin probably exerts its action by modifying the anerobic intestinal flora which dehydroxylate allocholic acid to allodeoxycholic acid; if so, this suggests that both hepatic and bacterial transformations are essential steps in the pathogenesis of cholestanol-induced cholelithiasis. The bile of rabbits on a normal diet contains allodeoxycholic acid (5% of total bile acids). A similar decrease in allodeoxycholic acid concentration and reciprocal increase in allocholic acid concentration is observed when neomycin is administered to rabbits on a normal diet.     

Effect of fish-fat or beef-fat supplemented diet on immune complex-induced entheropathy in the rat

In contrast to animals on a beef fat-supplemented diet (BFD), animals maitained on a fish fat-supplemented diet (FFD) incorporate increased amounts of eicosapentaenoic acid (EPA) into membrane phospholipids. Generation of lipid mediators from such tissues favors the formation of compounds with less pro-inflammatory activity than are derived from tissues poor in EPA. Nevertheless, the FFD has not had a uniformly beneficial effect on animal models of inflammatory diseases. We previously showed that intravenous injection of rat anti-BSA-BSA complexes (IC) prepared in 5x antigen excess rapidly induced a striate pattern of serosal (to mucosal) hemorrhage and vascular congestion throughout the small intestine. In this study, we tested the effect of a BFD and FFD on immune complex-induced enteropathy. After six (Expt. 1) or eight weeks (Expt. 2) on the diet, rats were injected with IC and the severity of serosal hyperemia in the small intestine was scored. In some FFD, no lesions were seen under conditions which elicited moderate to severe lesions in BFD rats. In Expt. 1 involving 22 rats and in Expt. 2 involving 28 rats, those on the FFD had a significantly lower composite lesional score compared to those on the BFD, p < 0.005 and p < 0.005, respectively. These results indicate that the FFD had a beneficial effect on IC-induced enteropathy. It is suggested that this effect of the FFD may be mediated primarily by a reduction in availability of platelet-activating factor.     

The use of rats associated with a human faecal flora as a model for studying the effects of diet on the human gut microflora

The activities of four bacterial biotransformation enzymes (beta-glucosidase, beta-glucuronidase, nitrate reductase and nitroreductase) were measured in the caecal contents of conventional flora rats or germ-free rats contaminated with a mixed, human faecal flora and compared with activities present in a fresh human stool preparation. Both the conventional flora rats and the rats inoculated with a human flora exhibited an enzyme profile generally similar to that of human faeces, although the conventional rat flora exhibited negligible nitrate reductase activity. The enzyme profile remained essentially unaltered in both human flora preparations following supplementation of the diet with pectin, whereas the conventional rat flora responded to this plant cell wall carbohydrate with a significant increase in nitrate reductase activity. The results demonstrate that enzymic activities of the human faecal microflora can be simulated in rats associated with a mixed population of human intestinal bacteria.     

The use of rats associated with a human faecal flora as a model for studying the effects of diet on the human gut microflora

The activities of four bacterial biotransformation enzymes (β-glucosidase, β-glucuronidase, nitrate reductase and nitroreductase) were measured in the caecal contents of conventional flora rats or germ-free rats contaminated with a mixed, human faecal flora and compared with activities present in a fresh human stool preparation. Both the conventional flora rats and the rats inoculated with a human flora exhibited an enzyme profile generally similar to that of human faeces, although the conventional rat flora exhibited negligible nitrate reductase activity. The enzyme profile remained essentially unaltered in both human flora preparations following supplementation of the diet with pectin, whereas the conventional rat flora responded to this plant cell wall carbohydrate with a significant increase in nitrate reductase activity. The results demonstrate that enzymic activities of the human faecal microflora can be simulated in rats associated with a mixed population of human intestinal bacteria.     

小肠细菌过生长与非酒精性脂肪性肝炎的关系初步研究

目的：调查小肠细菌过生长在非酒精性脂肪性肝炎病人中的发生率。方法：研究病例包括非酒精性脂肪性肝炎39例、慢性乙型肝炎47例、健康对照27例。小肠细菌过生长以乳果糖H2呼气试验诊断。结果：小肠细菌过生长在非酒精性脂肪性肝炎的发生率为45．7％,慢性乙型肝炎为32．5％,健康对照4．2％,前二组差异无显著性,但都显著高于对照组。结论：小肠细菌过生长在非酒精性脂肪性肝炎病人有较高的发生率,但其因果关系尚需阐明。     

The Role of Intestinal Microbiota in Development of Irinotecan Toxicity and in Toxicity Reduction through Dietary Fibres in Rats

CPT-11 is a drug used as chemotherapy for colorectal cancer. CPT-11 causes toxic side-effects in patients. CPT-11 toxicity has been attributed to the activity of intestinal microbiota, however, intestinal microbiota may also have protective effects in CP!-11 chemotherapy. This study aimed to elucidate mechanisms through which microbiota and dietary fibres could modify host health. Rats bearing a Ward colon carcinoma were treated with a two-cycle CPT-11/5-fluorouracil therapy recapitulating clinical therapy of colorectal cancer. Animals were fed with a semi-purified diet or a semi-purified diet was supplemented with non-digestible carbohydrates (isomalto-oligosaccharides, resistant starch, fructo-oligosaccharides, or inulin) in 3 independent experiments. Changes in intestinal microbiota, bacteria translocating to mesenteric lymphnodes, cecal GUD activity, and cecal SCFA production, and the intestinal concentration of CPT-11 and its metabolites were analysed. Non-digestible carbohydrates significantly influenced feed intake, body weight and other indicators of animal health. The identification of translocating bacteria and their quantification in cecal microbiota indicated that overgrowth of the intestine by opportunistic pathogens was not a major contributor to CPT-11 toxicity. Remarkably, fecal GUD activity positively correlated to body weight and feed intake but negatively correlated to cecal SN-38 concentrations and IL1-β. The reduction in CPT-11 toxicity by non-digestible carbohydrates did not correlate to stimulation of specific bacterial taxa. However, cecal butyrate concentrations and feed intake were highly correlated. The protective role of intestinal butyrate production was substantiated by a positive correlation of the host expression of MCT1 (monocarboxylate transporter 1) with body weight as well as a positive correlation of the abundance of bacterial butyryl-CoA gene with cecal butyrate concentrations. These correlations support the interpretation that the influence of dietary fibre on CPT-11 toxicity is partially mediated by an increased cecal production of butyrate.     

实验大鼠肝性病肠道菌群失调与血氨的关系

目的　探讨肝性脑病实验大鼠肠道菌群失调对血氨浓度的影响。方法　Wistar大鼠4 0只,随机分为4组,其中3组制备肝性脑病模型,剩余1组为正常对照组,分别以灌胃给药,以需氧、厌氧法及血浆除蛋白滤液法检测肠道菌群及血浆中血氨含量。结果　肝性脑病与正常对照组比较,有明显的肠道菌群失调症,同时伴有血氨浓度显著升高( P<0 .0 5 )。结论　实验大鼠肠道菌群失调可引起大鼠血浆内血氨浓度明显升高,进而引发肝性脑病及亚临床肝性脑病     

Selective decontamination by antimicrobials during long term treatment: perspectives for saving host indigenous microbiota

Short bowel syndrome (SBS) occurs in patients fed total parenteral nutrition (TPN) after massive intestinal resection. TPN weaning is often associated with occlusion or sepsis. In the present study the intestinal biotope was investigated in young patients (n = 14) with massive intestinal resection and recurrent symptoms of sepsis or occlusion during enteral food introduction. They were treated by aminosides for a long term period. Ileal effluents were collected for enumerating bacteria. In some case, blood and rectal specimen were also collected. A few patients developed bacterial overgrowth (1), occlusion (1), sepsis (4), osteoarthritis (1) or pneumonia (1) during the survey. A drastic drop of bifidobacteria that was not prevented by human milk feeding was observed prior occlusion or respiratory infection. Detection of clostridial vegetative forms preceded sepsis and decrease in clostridia parallelled recovery. In conclusion, onset of symptoms was related with extreme imbalance of the ileal flora. Supplementation with bifidobacterial compounds that were well tolerated in two patients could be of interest in children with recurrent symptoms.     

The Intestinal Flora in Pigs With Parakeratosis

Two groups of pigs, groups I and II, were self-fed a basal diet. The composition of the diet is listed in Table 1. Another group, group III, was fed the same diet with the fish meal (Icelandic codmeal) replaced by Peruvian sardine meal. The composition of the intestinal flora in the pigs of group I and II was influenced by the diet with a great increase in the clostridial counts. Concomitant with the change in the anaerobic flora, skin changes which ultimately developed into typical parakeratosis, appeared on those pigs which did not receive supplementary zinc. In group III no change of the intestinal flora could be detected and no skin changes appeared in this group.     

Bacteria-lectin interactions in phytohemagglutinin-induced bacterial overgrowth of the small intestine

The mechanism of phytohemagglutinin-induced bacterial overgrowth of the small bowel in the rat was studied. Interaction of the lectin with bacterial isolates selected at random from those that comprised the major population of the overgrowth was determined. In both bacterial agglutination assays and glycocalyx stabilization, no specific association between lectin and bacteria was seen. In three independent binding assays phytohemagglutinin was not found to increase bacterial adherence to washed intestinal mucosa. Phytohemagglutinin would not appear to act, therefore, as a direct ligand to mediate bacterial adherence or to modify the mucosal surface to increase bacterial adherence.     

肠道菌群及其代谢产物与T2DM发病机制及干预措施*

2型糖尿病(type 2 diabetes mellitus,T2DM)是一种因胰岛素分泌不足或胰岛素抵抗而引起的慢性代谢疾病,T2DM患病人数的快速增长使治疗和预防T2DM成为世界上亟待解决的医学问题。随着微生物组学技术的进步,肠道菌群及其代谢产物与T2DM的研究亦逐渐深入,肠道菌群可能成为治疗和预防T2DM的靶点。肠道菌群及其代谢产物作用于T2DM的潜在机制,主要是参与体内炎症反应、增加肠道短链脂肪酸产量、调节肠道胆汁酸的代谢、调节支链氨基酸的代谢等。目前,治疗T2DM的药物可能会产生一些副作用,而基于肠道菌群干预T2DM的措施相对安全无害。例如,可通过严格控制的特定结构饮食长期摄入或增加益生菌的长期摄取控制血糖,或通过口服可影响肠道菌群生态结构的降糖药物(二甲双胍、阿卡波糖)有效地调控血糖水平。综述基于肠道菌群及其代谢产物诱发T2DM的潜在机制,研讨基于肠道菌群干预T2DM的措施,从肠道菌群的新视角探索治疗T2DM的新方法,为彻底治疗T2DM提供一种新可能。     

Does the intestinal bifidobacterial colonisation affect bacterial translocation?

The aim of this work was to investigate the possible role of the intestinal anaerobic flora (especially bifidobacteria) in regulating bacterial translocation (BT) which can be defined as the passage of intestinal microbes through the mucosa to internal organs. Default in BT regulation concurs with pathogenesis of sepsis in various human conditions, such as acute pancreatitis, cirrhosis, necrotising enterocolitis or multiple organ failure. The intestinal flora was studied in human flora associated mice (HF mice) and BT was quantified in Peyer's patches (PP), blood, spleen, liver and lungs. HF mice displayed a heterogenic intestinal colonisation with bifidobacteria. High colonisation of both caecum and colon by bifidobacteria led to a poorer bacterial contamination of blood, liver and lungs. Moreover, ileal, caecal and colonic bifidobacterial counts negatively correlated with the bacterial dissemination (number of contaminated organs per mouse). In contrast, Bacteroides fragilis group counts positively correlated with bacteraemia, lungs contamination or bacterial dissemination. Additionally, clostridia localised in the colon affected bacterial uptake by PP and lungs contamination as indicated by positive correlations between bacterial populations in these respective locations. These results indicate that bifidobacteria, when established in high counts, reduced BT to liver, blood and lungs, whereas B. fragilis group favoured the bacterial passage. Clostridia established in the distal ileum also seemed to favour BT to lungs. The manipulation of the bacterial flora to optimise the regulatory effect on BT should therefore focus on the selective promotion of bifidobacteria and avoid an increase in potentially detrimental populations such as B. fragilis group and clostridia.     

非酒精性脂肪性肝炎患者肠道菌群失调与肠道通透性及血清内毒素的相关性研究

目的 探讨非酒精性脂肪性肝炎患者肠道菌群失调与肠道通透性及血清内毒素的相关性.方法 选择肠道菌群中具有代表性的细菌共8种进行培养.研究对象为健康成人(A组)和非酒精性脂肪性肝炎(B组)各30例,计数两组肠道菌群中8种细菌的数量,检测所有被研究者的血清内毒素、二胺氧化酶(DAO)、D-乳酸及TNF-α的浓度,比较两组细菌数量和血清指标的变化,并进行相关分析.结果 与A组比较,B组双歧杆菌、乳杆菌和拟杆菌的菌落数显著减少(P＜0.01或P＜0.05),而肠球菌、肠杆菌的菌落数则有显著增加(P＜0.01或P＜0.05);酵母真菌、葡萄球菌、梭菌菌落数没有发生显著改变(P＞0.05);血清内毒素、DAO、D-乳酸、TNF-α水平显著增高(P＜0.01);相关分析显示肠杆菌与内毒素、DAO、D-乳酸相关(r=0.644,P＜0.001;r=0.415,P=0.023;r =0.383,P=0.037);血清内毒素和DAO、D-乳酸、TNF-α显著相关(r=0.485,P=0.007;r=0.477,P=0.008;r=0.490,P=0.006);TNF-α则与DAO、D-乳酸相关(r=0.426,P =0.019;r =0.440,P=0.015).结论 非酒精性脂肪性肝炎患者存在肠道菌群失调、肠道通透性增高及肠源性内毒素血症,肠杆菌的过度生长与肠源性内毒素血症及肠道通透性密切相关.     

肠道菌群变化对实验小鼠肠黏膜免疫的影响

目的探讨肠道菌群变化对肠黏膜相关淋巴组织的影响。方法通过变性梯度凝胶电泳（Denatu-ring gradient gel electrophoresis,DGGE）法研究了三种不同级别实验小鼠即清洁级小鼠、SPF小鼠和普通小鼠肠道菌群的组成,并用免疫组织化学（immunohistochemistry,IHC）方法研究了此三种不同级别的实验小鼠肠黏膜相关淋巴组织sIgA阳性细胞分布情况。结果普通小鼠肠道细菌种类最多,其sIgA阳性细胞分布最多,肠道不同部位之间sIgA分布情况差异有显著性（P〈0.05）,小肠和大肠之间的阳性细胞分布差异极显著（P〈0.01）;其次是清洁级小鼠,其肠道不同部位之间菌种组成差异无显著性,小肠和大肠之间的阳性细胞分布差异有显著性（P〈0.05）;SPF小鼠肠道细菌种类最少,故其sIgA阳性细胞分布最少,且其肠道不同部位之间菌种组成差异无显著性,小肠和大肠之间的阳性细胞分布差异无显著性（P〉0.05）。结论随着动物微生物控制级别的增高,肠道微生物多样性递减;sIgA阳性细胞与肠道细菌种类正相关。