Studies of the route, magnitude, and time course of bacterial translocation in a model of systemic inflammation

Bacteria have been documented to translocate from the gut to systemic organs, yet the exact route by which they translocate remains unclear. To determine the route of bacterial translocation, different dosages of zymosan were used to activate complement and cause systemic inflammation. At a zymosan dose of 0.1 mg/g, bacteria translocated only to the mesenteric lymph node complex, whereas at a dose of 0.5 mg/g the bacteria translocated systematically. In rats receiving 0.5-mg/g doses of zymosan, the bacteria appeared to reach systemic organs via the portal blood rather than via the mesenteric lymph, as bacteria were present in 87% of portal blood samples but only 25% of lymph samples. The number of bacteria exiting the portal vein was 11,500 times greater than the number exiting via the lymph. Thus, both the route and extent of bacterial translocation varies based on the magnitude of the inflammatory insult, with the portal blood being the major route of bacterial translocation to systemic organs.     

Protein malnutrition predisposes to inflammatory-induced gut-origin septic states.

The development of an uncontrolled inflammatory response has been implicated in the pathogenesis of adult respiratory distress syndrome and multiple-organ failure. Because zymosan activates complement and induces a systemic inflammatory response, the effect of zymosan on intestinal structure and barrier function was measured in normally nourished (NN) and protein malnourished (PM) mice. Normally nourished and protein malnourished (up to 21 days) mice challenged intraperitoneally with zymosan (0.1 mg/g body weight) were killed 24 hours after zymosan challenge and their organs cultured for translocating bacteria. Zymosan-induced bacterial translocation was limited to the mesenteric lymph nodes of the NN mice, whereas translocating bacteria spread from the gut to the liver, spleen, and blood stream (p less than 0.05) in the PM mice. Zymosan-induced bacterial translocation appeared to be related primarily to the combination of mucosal injury and a disruption of the gut flora ecology in the PM mice and to mucosal injury in the NN mice. The extent of mucosal injury was greater the longer the mice were protein malnourished before zymosan challenge. The effect of zymosan on survival was measured in separate groups of mice. At a dose of 0.1 mg/g body weight, no deaths occurred in NN mice or in 7-day PM mice. However 20% of the 14-day PM mice and 80% of the 21-day PM mice receiving zymosan died. Thus PM predisposes to mucosal damage and the development of potentially lethal gut origin septic state during periods of systemic inflammation.     

Macrophage elimination increases bacterial translocation and gut-origin septicemia but attenuates symptoms and mortality rate in a model of systemic inflammation.

OBJECTIVE: The central question tested in this study was whether dichloromethylene-diphosphonate (CL2MDP) liposome-mediated elimination of hepatic and splenic macrophages would influence zymosan-induced bacterial translocation and the zymosan-induced generalized inflammatory response. SUMMARY BACKGROUND DATA: Both an uncontrolled activation of macrophages and the loss of intestinal barrier function have been implicated in the development of adult respiratory distress syndrome and multiple organ failure. METHODS: Macrophage elimination was accomplished by intravenous injection of 200 microL of CL2MDP-liposome suspension. Control mice received an intravenous injection of 200 microL of phosphate-buffered saline. Two days later, the animals were challenged intraperitoneally with zymosan suspended in paraffin to determine a dose-response curve (0.1, 0.5, or 1.0 mg/g body weight). Twenty-four hours after zymosan challenge, signs of systemic stress were determined, and bacterial translocation to the mesenteric lymph node, liver, spleen, and blood was measured. A separate mortality study was performed with a dose of 1.0 mg/g of zymosan suspension. RESULTS: The incidence of the systemic spread of bacteria was significantly increased in the macrophage-depleted mice. Although systemic bacterial translocation was promoted by macrophage elimination, the systemic toxic response was significantly decreased in all macrophage-depleted groups (p < or = 0.01). The 12-day mortality rate was 0% in the macrophage-depleted groups and 27% in the control group (p = 0.05). CONCLUSIONS: The lethal and toxic effects of zymosan appear to be related more to the excessive activation of macrophages than to the systemic spread of bacteria.     

肠道细菌移位的研究现状

目的 探讨肠道细菌移位研究的进展。方法 复习2000年至2005年6月关于肠道通透性的改变、肠道菌群失调和全身炎症反应综合征（SIRS）的文献。结果 随着对SIRS和MODS的深入研究,越来越多的证据显示,肠道不仅是MODs的靶器官,更是始动器官。只有保证了肠道黏膜屏障的完整性,才能有效的预防肠道细菌移位。去除原发病,保证肠道的血供和氧供是最基本的治疗方法。早期启动肠道、建立肠内营养以及选择性的肠道去污染也是有效的治疗手段。结论 随着对肠道细菌移位认识的深入,我们的治疗手段不断丰富,可以更有效预防肠道细菌移位的发生,并阻止向SIRS和MODS进一步发展。     

Gut-origin sepsis: Evolution of a concept

The concept of bacterial translocation and gut-origin sepsis as a cause of systemic infectious complications and the multiple organ dysfunction syndrome (MODS) in surgical and ICU patients has emerged over the last several decades, although the exact clinical relevance of these phenomena continues to be debated. Thus, the goal of this review is to trace the evolution of gut-origin sepsis and gut-induced MODS and put these disorders and observations into clinical perspective. Additionally, the mechanisms leading to gut-derived complications are explored as well as therapeutic options to limit or prevent these complications. From this work, several major conclusions emerge. First, that bacterial translocation occurs clinically and is responsible for increased infectious complications in patients undergoing major abdominal surgery. However, the phenomenon of bacterial translocation is not sufficient to explain the development of MODS in ICU patients. Instead, the development of MODS in these high-risk patients is likely due to gut injury and the systemic spread of non-microbial, tissue-injurious factors that reach the systemic circulation via the intestinal lymphatics. These observations have resulted in the gut-lymph hypothesis of MODS.     

Endotoxin-induced bacterial translocation: a study of mechanisms

Previously, we documented that nonlethal doses of endotoxin cause the translocation (escape) of bacteria from the gut to systemic organs. The purpose of this study was to determine which portion(s) of the endotoxin molecule induces bacterial translocation and to examine the role of xanthine oxidase activity in the pathogenesis of endotoxin-induced bacterial translocation. Nonlethal doses of Salmonella endotoxin preparations (wild type, Ra, or Rb), containing the terminal portion of the core polysaccharide, induced bacterial translocation, whereas those preparations lacking the terminal-3 sugars (Rc, Rd, Re, or lipid A) did not induce bacterial translocation. Additionally, only those endotoxin preparations that induced bacterial translocation injured the gut mucosa, increased ileal xanthine dehydrogenase and oxidase activity, and disrupted the normal ecology of the gut flora, resulting in overgrowth with enteric bacilli. Inhibition of xanthine oxidase activity by allopurinol prevented endotoxin (Ra)-induced mucosal injury and reduced the incidence of bacterial translocation from 83% to 30% (p less than 0.01). These results suggest that endotoxin-induced bacterial translocation requires the presence of the terminal core lipopolysaccharide moiety and that xanthine oxidase-generated oxidants are important in the pathogenesis of endotoxin-induced mucosal injury and bacterial translocation.     

Endotoxin induces bacterial translocation and increases xanthine oxidase activity

Previously, we documented that endotoxin induces bacterial translocation from the gut and that inhibition or inactivation of xanthine oxidase activity reduces endotoxin-induced bacterial translocation. Consequently, experiments were performed to correlate endotoxin-induced bacterial translocation with changes in intestinal mucosal structure and xanthine dehydrogenase and oxidase activity. Segments of the jejunum, ileum, cecum, proximal colon, distal colon, and liver were harvested from ICR mice 24 hr after IP administration of E. coli 0111:B4 endotoxin (0.1 mg). Xanthine dehydrogenase and oxidase activities were measured in these samples and correlated with intestinal morphology. Bacteria translocated from the intestines to extraintestinal organs in 70% of the mice receiving endotoxin, while the organs of control mice were sterile (p less than 0.01). Endotoxin injured primarily the ileal and cecal mucosa and increased ileal and hepatic xanthine dehydrogenase and cecal oxidase activities (p less than 0.05). These results suggest that xanthine oxidase-induced mucosal damage plays a role in endotoxin-induced bacterial translocation.     

Pancreatitis and nutrition. Significance of the gastrointestinal tract and nutrition for septic complications

Septic complications are an important factor for the morbidity and mortality of acute pancreatitis. The gut has been identified as a source of infection early in the course of the disease allowing intestinal bacteria to translocate into pancreatic necrosis and other organs. Bacterial translocation is promoted by an impaired intestinal mucosal barrier which can be attributed to the reduced oxygen and substrate supply of the intestine during the early systemic response to the pancreatic injury. A rat model of severe acute pancreatitis has been used to confirm the hypothesis that an impaired mucosal barrier can be stabilized by supplying certain nutritients, vitamins and trace elements. Following a discussion of the many aspects of bacterial translocation and gut derived sepsis, the role of the gut and nutrition for the development of septic complications in acute pancreatitis is summarized as follows: Early in the course of acute pancreatitis the gut is a target organ of the primary systemic inflammatory response (SIRS) to pancreatic injury. SIRS-induced gut barrier dysfunction promoting bacterial translocation makes the gut the motor for secondary (septic) complications. As a septic focus the gut becomes a target for therapeutic measures aimed at stabilizing the impaired gut barrier. Nutritive factors demonstrated to improve impaired gut barrier function include early enteral feeding and specific factors like glutamine which are essential for enterocytes and colonocytes in stress. Experimental data are presented to underline the significance of these nutritive factors and subsequent randomized multicenter trials performed to verify the positive experimental results are introduced. The effect of other nutritive factors (e.g. omega-3-fatty acids) has not yet been systemically investigated. Thus, experimental and clinical studies need to be performed for evaluating their effect on bacterial translocation and the disease course in acute pancreatitis.     

急性坏死性胰腺炎时肠屏障损害及肠源性细菌和内毒素移位的实验研究

目的 观察急性坏死性胰腺炎（ANP）时肠粘膜屏障的改变和肠源性细菌和内毒素移位。方法 将Wistar大鼠随机分为正常对照组（n=6)、假手术组（n=30)和ANP组（n=39)。采用人工胆汁胰管逆行灌注法制作ANP模型。观察胰腺、小肠病理改变和小肠粘膜上皮细胞间紧密连接（冷冻蚀刻电镜）变化。动态测定血浆D-乳酸、内毒素水平,以及腹腔脏器细菌移位率。结果 ANP后小肠粘膜损伤,皮皮细胞间紧密连接破坏甚至消失,血浆D-乳酸水平上升,发病早期即出现内毒素血症;ANP发生后72h脏器细菌移位率达到59.5%。结论 ANP早期肠粘膜屏障功能受损。导致肠道细菌和内毒素移位,成为全身炎症反应和胰腺继发感染的根源。     

Differential pathophysiology of bacterial translocation after thermal injury and sepsis.

Bacterial translocation (BT) occurs transiently after thermal injury and may result from an ischemic intestinal insult. To evaluate continued intestinal ischemia in the ongoing BT associated with sepsis after injury, rats were randomized to (1) 30% burn injury with Pseudomonas wound infection (BI), (2) BI + fluid resuscitation (BI + Fluid), (3) BI after allopurinol pretreatment to inhibit xanthine oxidase (BI + Allo), or (4) BI after azapropazone pretreatment to inhibit neutrophil degranulation (BI + Aza). On postburn days (PBD) 1, 4, and 7, animals were studied for evidence of BT and intestinal lipid peroxidation. BI + Fluid, BI + Allo, and BI + Aza significantly (p less than 0.05) reduced rates of BT and ileal lipid peroxidation acutely after thermal injury (PBD 1) compared to BI. All four groups had equally high rates of BT associated with the onset of sepsis (PBDs 4 and 7), without evidence of further intestinal lipid peroxidation. These data indicate that the chronic gut barrier failure associated with sepsis after injury occurs independently of continued intestinal ischemia.     

Genetic susceptibility to mucosal damage leads to bacterial translocation in a murine burn model

Since genetic factors may be important in host resistance to infections after thermal injury, we screened the susceptibility of three mouse strains (CD-1, Balb/c, and C57/bl) to thermally induced bacterial translocation from the GI tract. Bacteria translocated to the MLNs of Balb/c but not the CD-1 or C57/bl mice receiving 25% body burns. The increased incidence of bacterial translocation in the burned Balb/c mice appeared to be due to a burn-induced gut mucosal injury, since the intestinal mucosa of the Balb/c but not the CD-1 or C57/bl mice was damaged 24 hr after the thermal injury. The mucosal injury appears to be mediated, at least in part, by xanthine oxidase-generated oxygen-free radicals, since inhibition of xanthine oxidase activity with allopurinol, or inactivation of xanthine oxidase activity by a molybdenum-free tungsten diet, prevented the mucosal injury and reduced the extent of bacterial translocation.     

大鼠烫伤后肠道细菌IgA包被率变化的动态观察

目的探讨导致烧伤后肠源性感染的免疫学因素。方法建立肠道细菌免疫球蛋白Ａ（ＩｇＡ）包被率的检测方法，对烫伤大鼠肠道细菌ＩｇＡ包被率的变化和肠道细菌移位率的变化进行了动态观察。结果４０％体表面积烫伤后早期肠道细菌移位率明显升高，而后逐渐下降至伤前水平；各时相点肠道细菌的ＩｇＡ包被率明显降低。结论烧伤后肠道免疫屏障受到损伤，伤后肠道内ＩｇＡ保护功能的减弱可促使肠道细菌移位，与烧伤后脓毒症的发生、发展有密切关系。     

Endotoxin promotes the translocation of bacteria from the gut

Experiments were performed in mice to determine whether endotoxin could cause bacteria normally colonizing the gut to spread systemically, a process termed bacterial translocation. Endotoxin given intraperitoneally promoted bacterial translocation in a dose-dependent fashion from the gut to the mesenteric lymph node (MLN). The incidence of bacterial translocation to the MLN was similar whether the endotoxin was administered intramuscularly or intraperitoneally, although the number of bacteria colonizing the MLN was greater with intraperitoneal endotoxin. The incidence and magnitude of endotoxin-induced bacterial translocation were similar between CD-1 and C3H/HeJ (endotoxin-resistant) mice, indicating that bacterial translocation is not prevented by genetic resistance to endotoxin. Thus, it appears that the gut may serve as a reservoir for bacteria causing systemic infections during endotoxemia.     

Lack of correlation between failure of gut barrier function and septic complications after major upper gastrointestinal surgery

OBJECTIVE: To determine the influence of abnormal gut barrier function on the risk of septic complications in patients undergoing major resectional surgery for upper gastrointestinal cancer. SUMMARY BACKGROUND DATA: A failure of the gut mucosal barrier to exclude bacteria and endotoxin from the portal and systemic circulation is incriminated in the development of sepsis and multiple organ failure. Although the experimental data is compelling, corroborative evidence from studies in humans is sparse. This study attempted to correlate both preoperative gut barrier dysfunction and the pattern of change after surgery with septic outcome. METHODS: Sixty-eight patients undergoing curative resectional surgery for upper gastrointestinal cancer were monitored for 30-day septic morbidity (intraabdominal abscesses/empyema and pneumonia). Intestinal permeability, serum IgM and IgG anti-endotoxin antibodies (EndoCAb), and serum C-reactive protein were measured before surgery and on postoperative days 1 and 7. RESULTS: Increased intestinal permeability before surgery did not predict septic outcome. Major surgery was associated with increased intestinal permeability and evidence of endotoxin exposure. Comparing sepsis and nonsepsis groups, however, there was no significant difference in intestinal permeability, endotoxin exposure, and the acute phase response after surgery. CONCLUSIONS: This study demonstrates that gut barrier dysfunction occurs after surgery, but the magnitude of change does not differentiate patients in whom sepsis develops and those in whom it does not. Preoperative increased intestinal permeability had no predictive value for sepsis. This study failed to support the thesis that gut barrier dysfunction is directly linked to sepsis.     

Glutamine stabilizes intestinal permeability and reduces pancreatic infection in acute experimental pancreatitis

Intestinal barrier failure and subsequent translocation of bacteria from the gut play a decisive role in the development of systemic infections in severe acute pancreatitis. Glutamine (GLN) has been shown to stabilize gut barrier function and to reduce bacterial translocation in various experimental settings. The aim of this study was to evaluate whether GLN reduces gut permeability and bacterial infection in a model of acute necrotizing pancreatitis. Acute necrotizing pancreatitis was induced in 50 rats under sterile conditions by intraductal infusion of glycodeoxycholic acid and intravenous infusion of cerulein. Six hours after the induction of pancreatitis, animals were randomly assigned to one of two groups: standard total parental nutrition (TPN) or TPN combined with GLN (0.5 g/kg⁻¹/day⁻¹). After 96 hours, the animals were killed. The pancreas was prepared for bacteriologic examination, and the ascending colon was mounted in a Ussing chamber for determination of transmucosal resistance and mannitol flux as indicators of intestinal permeability. Transmucosal resistance was 31% higher in the animals treated with GLN-supplemented TPN compared to the animals given standard TPN. Mannitol flux through the epithelium was decreased by 40%. The prevalence of pancreatic infections was 33% in animals given GLN-enriched TPN as compared to 86% in animals receiving standard TPN (P < 0.05). Adding GLN to standard TPN not only reduces the permeability of the colon but decreases pancreatic infections in acute necrotizing pancreatitis in the rat. This confirms previous reports that GLN decreases bacterial translocation by stabilizing the intestinal mucosal barrier. The present findings provide the first evidence suggesting that stabilizing the intestinal barrier can reduce the prevalence of pancreatic infection in acute pancreatitis and that GLN may be useful in preventing septic complications in clinical pancreatitis.     

Hemorrhagic shock-induced bacterial translocation is reduced by xanthine oxidase inhibition or inactivation

Experiments were performed to determine whether bacterial translocation (BT) after hemorrhagic shock is due to a reperfusion injury mediated by xanthine oxidase-derived oxidants. Rats were subjected to 30 minutes of shock (30 mm Hg) followed by reinfusion of shed blood. Twenty-four hours after hemorrhage and reinfusion, the mesenteric lymph node, liver, and spleen were harvested from each animal for bacterial culture, and the ileum and cecum were examined histologically. Sham-shocked (control) rats were instrumented, but blood was not withdrawn. The incidence of BT was higher in the shocked rats (61%) than in the sham-shocked animals (7%) (p less than 0.01). Allopurinol (50 mg/kg, administered orally), a competitive inhibitor of xanthine oxidase, reduced the incidence of shock-induced BT to 14% (p = 0.02). Similarly, rats fed a tungsten-supplemented molybdenum-free diet, which inactivates xanthine oxidase, reduced shock-induced BT to 10% (p = 0.02). The histologic damage cause by hemorrhagic shock was prevented by blocking xanthine oxidase activity. Thus hemorrhagic shock-induced bacterial translocation from the gut appears to be mediated by oxidants generated by activation of the xanthine oxidase system.     

The role of the gastrointestinal tract in postinjury multiple organ failure

Despite intensive investigation, the pathogenesis of postinjury multiple organ failure (MOF) remains elusive. Laboratory and clinical research strongly implicate that the gastrointestinal tract plays a pivotal role. Shock with resulting gut hypoperfusion appears to be one important inciting event. While early studies persuasively focused attention on bacterial translocation as a unifying mechanism to explain early and late sepsis syndromes that characterize postinjury MOF, subsequent studies suggest that other gut-specific mechanisms are operational. Based on our Trauma Research Center observations and those of others, we conclude that: 1) bacterial translocation may contribute to early refractory shock; 2) for patients who survive shock, the reperfused gut appears to be a source of proinflammatory mediators that may amplify the early systemic inflammatory response syndrome; and 3) early gut hypoperfusion sets the stage for progressive gut dysfunction such that the gut becomes a reservoir for pathogens and toxins that contribute to late MOF.     

Gut barrier function and the surgeon

There is accumulating evidence that multiple organ failure is not always the result of an established septic focus. Increasing attention has centred on the gut as a reservoir of bacteria (and bacterial endotoxins) that can traverse the intestinal mucosal barrier (a process called 'bacterial translocation') and initiate the septic state. Although the link between haemorrhagic shock and sepsis was recognized decades ago, the full experimental demonstration of this phenomenon is more recent. It was shown to occur in three main settings: physical disruption of the gut mucosa, impaired defence mechanisms and altered gut microbial ecology. Conditions such as haemorrhagic shock, burns, protein malnutrition and sepsis are seen in the severely ill surgical patient or the multiply injured, and are known to cause various combinations of circumstances favourable to bacterial translocation and endotoxin absorption. These may play an important role in the mortality of the critically ill.     

Anti-endotoxin hyperimmune globulin attenuates portal cytokinaemia, phagocytic cell priming, and acute lung injury after lower limb ischaemia-reperfusion injury.

OBJECTIVES: Acute limb ischaemia is a common and often lethal clinical event. Reperfusion of an ischaemic limb has been shown to induce a remote gut injury associated with transmigration of endotoxin into the portal and systemic circulation, which in turn has been implicated in the conversion of the sterile inflammatory response to a sepsis syndrome, after lower torso ischaemia-reperfusion injury. This study tests the hypothesis that an anti-endotoxin hyperimmune globulin attenuates ischaemia-reperfusion (I/R) associated sepsis syndrome. DESIGN: Prospective, randomised placebo controlled trial, animal experiment. MATERIALS AND METHODS: Experimental porcine model, bilateral hind limb I/R injury, randomised to receive anti-endotoxin hyperimmune globulin or placebo. RESULTS: Bilateral hind limb I/R injury significantly increased intestinal mucosal acidosis, portal endotoxaemia, plasma cytokine (TNF-alpha, IL-6, IL-8) concentrations, circulating phagocytic cell priming and pulmonary leukosequestration, oedema, and capillary-alveolar protein leak. Conversely, pigs treated with anti-endotoxin hyperimmune globulin (IgG) 20mg/kg at onset of reperfusion had significantly reduced portal endotoxaemia, early circulating phagocytic cell priming, plasma cytokinaemia and attenuation of acute lung injury. CONCLUSIONS: Endotoxin translocation across a hyperpermeable gut barrier, phagocytic cell priming and cytokinaemia are key events of limb I/R injury induced systemic inflammation and acute lung injury. This study shows that an anti-endotoxin hyperimmune globulin attenuates portal endotoxaemia, which may reduce early phagocytic cell activation, cytokinaemia and ultimately acute lung injury.     

小肠移植与肠道细菌移位

目的　探讨小肠移植后肠道细菌移位的原因和防治方法。方法　综述小肠移植与肠道细菌移位的相关文献。结果　移植小肠缺血再灌注损伤 ,免疫排斥反应 ,移植物抗宿主病和免疫抑制剂的应用都会导致肠粘膜屏障功能损害 ,肠蠕动和运输功能紊乱 ,肠道内条件致病菌过度生长 ,细菌和毒素向肠外组织器官移位 ,引起受体感染。结论　小肠移植后肠道细菌移位的发生率较高 ,是引起受体感染 ,影响预后的一个主要因素。提高肠移植外科技能 ,缩短缺血保存时间 ,选择性肠道去污 ,改进营养支持和免疫抑制方案 ,有望减少肠移植后细菌移位 ,降低感染并发症 ,提高预后指标。