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.     

Obstructive jaundice promotes bacterial translocation from the gut

Experiments were performed to determine if obstructive jaundice promotes the translocation of bacteria from the gastrointestinal tract to visceral organs. Three groups of mice were studied: control (n = 20), sham ligated (n = 28), and bile duct ligated (n = 33). The sham-ligated group underwent laparotomy and manipulation of the portal region, whereas the ligated group had their common bile ducts ligated. Seven days later, the mice were killed, their organs cultured, and the gastrointestinal tract examined histologically. The bilirubin levels of the ligated group (18.7 mg/dL) were elevated compared with the other groups (0.5 mg/dL) (p less than 0.05). The incidence of bacterial translocation was higher in the ligated (33%) than in the control (5%) or sham-ligated (7%) groups (p less than 0.05). Since bile is important in binding endotoxin and maintaining a normal intestinal microflora, cecal bacterial populations were quantitated. The cecal levels of gram-negative, enteric bacilli were 100-fold higher in the bile duct-ligated mice in which bacterial translocation occurred (p less than 0.05), indicating that intestinal bacterial overgrowth was a major factor responsible for bacterial translocation. The mucosal appearance of the intestines from the control and sham-ligated groups was normal. In contrast, subepithelial edema involving the ileal villi was present in the ligated group. In conclusion, the absence of bile within the gastrointestinal tract allows intestinal overgrowth with enteric bacilli and the combination of bacterial overgrowth and mucosal injury appears to promote bacterial translocation.     

Total parenteral nutrition promotes bacterial translocation from the gut

Bacterial translocation from the gut may be the primary event in many disease processes. The purpose of this study was to examine the route of nutrient administration on bacterial translocation from the gut. Each of 90 female Fischer rats underwent placement of a central venous catheter and was randomized to one of three groups. Group I (control) received food and water ad libitum. Group II received standard TPN solution orally from a bottle sipper and drank the solution ad libitum. Group III underwent TPN via the central catheter by pair feeding of the animals with group II. Animals were fed for 2 weeks, and liver, spleen, mesenteric lymph nodes, blood, and cecum were aseptically obtained for culture. A statistically significant difference (p less than 0.014) was found between translocation rates of parenterally fed animals compared with enterally fed animals. Two thirds of the animals (18/27) fed parenterally had culture-positive mesenteric lymph nodes compared with one third (9/27) of the enterally fed group and none (0/30) of the control group. A statistically significant increase in the cecal bacterial count was demonstrated in the animals fed the TPN solution, independent of route. Parenteral nutrition promotes bacterial translocation from the gut by increasing the cecal bacterial count and impairing intestinal defense.     

Food without fiber promotes bacterial translocation from the gut

To determine whether the route and/or composition of nutritional support alters intestinal barrier function (measured as bacterial translocation), rats were divided into three groups: food (controls), intravenous total parenteral nutrition (IV-TPN) fed, and oral total parenteral nutrition (ORAL-TPN) fed. Bacterial translocation did not occur in the rats that were fed normally, but did occur in 60% of the rats fed the IV-TPN or the ORAL-TPN diets for 7 days (p less than 0.05). Since both the IV-TPN and ORAL-TPN diets induced bacterial translocation and the TPN solution (28% glucose and 4.5% amino acids) lacks fiber, two additional groups of rats were fed orally 2.5 gm cellulose powder/day plus TPN solution by either the intravenous or the oral route. The addition of cellulose powder decreased the incidence of bacterial translocation to 8% in the group fed the ORAL-TPN diet and to 0% in the group fed the IV-TPN diet. Cellulose improved intestinal barrier function, even though it did not prevent bacterial overgrowth or the loss of mucosal mass in the rats fed the IV-TPN or ORAL-TPN diets. Cellulose powder appears to have prevented bacterial translocation primarily by preventing IV-TPN- or ORAL-TPN-induced alterations in mucosal structure. Thus the oral administration of this fiber maintains intestinal barrier function and prevents bacterial translocation even in the absence of oral nutrients.     

Effect of starvation, malnutrition, and trauma on the gastrointestinal tract flora and bacterial translocation

We have previously shown, in an animal model, that viable indigenous bacteria will cross the intact gastrointestinal (GI) mucosa and spread systemically, a process termed bacterial translocation, if the normal bacterial ecology of the gut was sufficiently disrupted to allow bacterial overgrowth or if the animals were severely immunosuppressed. Starvation or protein malnutrition disrupts the normal indigenous GI tract microflora and impairs host antibacterial defenses. Consequently, we tested the effect of the combination of starvation or protein malnutrition plus burn trauma in promoting bacterial translocation from the GI tract. Bacterial translocation was measured by quantitatively culturing the mesenteric lymph nodes, spleens, livers, blood, and peritoneal cavities of normal or burned (30% of total body surface area) CD1 mice deprived of food for three days or fed a low-protein (0.03%) diet. The effect of starvation or protein malnutrition on the gut microflora was determined by quantitatively measuring the levels of bacteria present in the ceca. Both starvation and protein malnutrition increased the cecal levels of gram-negative enteric bacilli and decreased the levels of lactobacilli and strict anaerobes. Surprisingly, neither starvation nor protein malnutrition promoted bacterial translocation, even though these animals lost over 20% of their body weight and the ecology of the gut microflora was disrupted. In fact, the protein-malnourished animals exhibited lower incidences of bacterial translocation than normally nourished animals when both groups were monoassociated with Escherichia coli C-25 or monoassociated and burned. Thus, it appears that protein malnutrition does not promote bacterial translocation, even when combined with burn trauma.     

Intestinal bacterial translocation in experimentally burned mice with wounds colonized by Pseudomonas aeruginosa.

Translocation of micro-organisms from the gastrointestinal tract may play a role in the pathogenesis of septic complications in severely burned patients. We therefore investigated the influence of burn wound infection with Pseudomonas aeruginosa on translocation in experimentally burned mice. The P. aeruginosa disseminated in 15% of the animals on the second day and in 20% of the animals on the third day postburn in the Pseudomonas-seeded group. Wound colonization with P. aeruginosa, compared with a control group, led to an increased incidence of translocation of Escherichia coli from the GI tract to the spleen (p < 0.005), liver (p < 0.03), lungs (p < 0.005), and peritoneal cavity (p < 0.03) on the second day postburn but not on the third day postburn. On both the second and third days, the number of viable E. coli in the organs in the Pseudomonas-seeded group exceeded that in the organs in the control group. In this model translocation of E. coli from the GI tract played a more important role than did hematogeneous dissemination of P. aeruginosa from the burn wound.     

Effect of polymyxin B on intestinal bacterial translocation in Pseudomonas aeruginosa wound-colonized burned mice.

Bacterial translocation (BT) from the gastrointestinal tract has been proposed to play a role in the pathogenesis of septic complications in severely burned patients. In a burn model the effect of a subtherapeutic dose of polymyxin B-sulfate (PB) at BT was examined in Escherichia coli-monoassociated mice with Pseudomonas aeruginosa-inoculated burn wounds. The BT incidence and number of translocating microorganisms to the spleen (p less than 0.01), liver (p less than 0.01), lung (p less than 0.05) and heart (p less than 0.05) were diminished significantly in the PB-treated versus the untreated group. Endotoxin in plasma was detectable in one of the 16 PB-treated versus 6 of the 17 control mice (p less than 0.05). The relation of Pseudomonas burn wound inoculation, BT, endotoxin and the endotoxin-neutralizing properties of PB will be discussed.     

Hemorrhagic shock induces bacterial translocation from the gut

Sepsis and multiple organ failure are common after hemorrhagic shock. The goal of the current experiments was to determine whether hemorrhagic shock would promote the translocation of bacteria from the gut to visceral organs. Twenty-four hours after being subjected to sham shock, or 30, 60, or 90 minutes of shock (30 mm Hg), rats were sacrificed and their organs quantitatively cultured for translocating bacteria. There was a direct relationship between the duration of hemorrhagic shock and the 24-hour mortality rate (p = 0.02). Bacteria did not translocate from the gut in the sham-shock rats, but did translocate to the mesenteric lymph nodes, livers, and spleens of the rats subjected to hemorrhagic shock (p less than 0.01). Rats subjected to 90 minutes of shock shock exhibited a greater degree of bacterial translocation than rats receiving 30 or 60 minutes of shock (p less than 0.05). The most common translocating bacteria were Escherichia coli and Enterococcus. Hemorrhagic shock injured the gut mucosa and caused subepithelial edema and focal areas of necrosis. Thus hemorrhagic shock followed by reinfusion of shed blood disrupts the gut barrier and allows indigenous bacteria normally contained within the gut to cause systemic infections.     

Thermal injury promotes bacterial translocation from the gastrointestinal tract in mice with impaired T-cell-mediated immunity

We have shown previously that after thermal trauma viable bacteria will cross the intact gastrointestinal mucosa (bacterial translocation) to invade the mesenteric lymph nodes and other organs if the normal indigenous microflora is disrupted, allowing bacterial overgrowth. To determine whether T-cell-mediated immunity (T-CMI) was important in preventing translocation after thermal injury in animals with an intact normal flora, conventional (+/+), athymic (nu/nu), and heterozygous (nu/+) mice receiving a 30% third-degree burn were killed at various intervals after burn and their organs cultured. Bacterial translocation did not occur in control or burned specific pathogen-free mice with intact T-CMI but did occur in athymic mice with deficient T-CMI. Both the incidence of positive organs and the numbers of translocated bacteria per gram of organ were increased after thermal injury. Bacterial overgrowth was not responsible for these findings, since the levels of cecal enteric bacteria were not different between the burned and nonburned groups. Since translocation occurred to a greater extent in athymic burned mice than control athymic mice, it appears that a thermal injury promotes translocation by impairing other host defense systems in addition to the T-CMI.     

Antibiotic prophylaxis diminishes bacterial translocation but not mortality in experimental burn wound sepsis

Pseudomonas (PSA) burn wound sepsis results in prolonged bacterial translocation (BT) of enteric organisms such as E. coli to the mesenteric lymph nodes (MLN) and organs in rats. Intestinal decontamination with oral antibiotics may improve mortality after burn injury, perhaps due to decreased BT. To determine the effect of oral antibiotic prophylaxis effective against E. coli but not PSA on BT and subsequent mortality in a model of PSA burn wound sepsis, rats were given a 30% scald burn and wound inoculation with 10(8) PSA followed by randomization to either ampicillin (50 mg/kg/d) or saline gavage. Cultures of MLN, organs, blood, and cecal contents were obtained on days 1, 4, and 7 after injury, with additional animals observed for 14-day mortality. Although oral antibiotic prophylaxis resulted in increased cecal colony counts, the incidence of BT was unchanged. The number of organisms present in both the MLN and organs, however, was significantly reduced with prophylaxis, indicating cecal overgrowth by non-translocating bacteria. Reduction of the number of translocating organisms did not result in improved mean survival time after injury, suggesting that mortality from PSA burn wound sepsis occurs independently of bacterial translocation.     

Enteral nutrition prevents bacterial translocation but does not improve survival during acute pancreatitis

OBJECTIVE: To evaluate the effect of enteral nutrition (EN) in attenuating bacterial and/or endotoxin translocation, maintaining immune responsiveness, and improving outcome in early acute pancreatitis (AP) in Wistar male rats. DESIGN: Acute pancreatitis was induced in rats receiving total parenteral nutrition (TPN) (AP/TPN group) (n=34) and EN (AP/EN group) (n=35) by pressure injection of 1% deoxycholate into the biliopancreatic duct (0.6 mg/kg of body weight). Rats in the sham/TPN and sham/EN groups (n=10 each) underwent laparotomy without induction of AP. Catheters for TPN and EN were placed into the external jugular vein and jejunum, respectively. Rats were infused with Ringer lactate solution for 48 hours followed by TPN in the AP/TPN and sham/TPN groups, and EN in the AP/EN and sham/EN groups until day 7. The fluid volume and energy (calories) intake were similar in all groups. SETTING: Medical school research laboratory. MAIN OUTCOME MEASURES: Survival, blood endotoxin level, villus height, 5-bromo-2'-deoxyuridine (BrdU) uptake in the jejunum and ileum, bacterial culture of mesenteric lymph nodes, and CD4/CD8 ratio of T cells in mesenteric lymph nodes, spleen, and peripheral blood. RESULTS: There was no difference in survival and pancreatic healing between the AP/TPN and AP/EN groups. Colony-forming units of the mesenteric lymph nodes and the endotoxin level were significantly lower in the AP/EN group than in the AP/TPN group (P<.05). Villus height and BrdU intake was significantly higher in the AP/EN group than in the AP/TPN group (P<.05). The CD4/CD8 ratio of T cells in spleen and peripheral blood was higher in the AP/EN group than in the AP/TPN group (P<.05), whereas there was no difference in mesenteric lymph nodes. CONCLUSIONS: Jejunal administration of EN is well tolerated in early AP, maintains immune responsiveness and gut integrity, and reduces bacterial and/or endotoxin translocation. However, compared with TPN, EN does not improve outcome. These results suggest that factors other than bacterial and/or endotoxin translocation may be responsible for mortality in this rat model of early AP. However, additional studies of both early bacterial and/or endotoxin translocation and late assessment of outcome are indicated.     

Absence of intestinal bile promotes bacterial translocation.

Previously, the authors documented that extrahepatic biliary obstruction promotes the systemic translocation of bacteria from the intestine to visceral tissues. The current experiments were performed to determine whether it was the absence of intestinal bile or the presence of biliary obstruction that promoted bacterial translocation. Four groups of rats were studied: 1) nonoperated controls (n = 20), sham common bile duct-ligated (n = 22), common bile duct-ligated (n = 25), and common bile duct-diverted (choledochovesical bypass) (n = 23). The sham-ligated group underwent laparotomy and manipulation of the portal region; whereas the ligated group had their common bile ducts ligated, while the choledochovesical group had a silastic tube placed from the common bile duct to the bladder. Seven days later, at death, the incidence of bacterial translocation was higher in the groups of rats subjected to common bile duct ligation (41%) or diversion (32%) than in the control (3%) or sham-ligated (5%) groups (P less than 0.05). Histologic sections of ileums of ligated and diverted animals both showed subepithelial edema. These findings suggest that it is primarily the absence of bile in the intestine that promotes mucosal injury and bacterial translocation and not biliary obstruction.     

Effect of stress and trauma on bacterial translocation from the gut

Previously, we established that bacteria contained within the gut can cross the GI mucosal barrier and spread systemically, a process termed bacterial translocation. Three models were used to extend this work: cold exposure (up to 16 hr at 4 degrees C), a nontissue injury stress model; femoral fracture-amputation, a trauma model; and thermal injury (30% third-degree burn), a trauma model with retained necrotic tissue. CD-1 mice either with a normal GI microflora or who were monoassociated with Escherichia coli C-25 were subjected to sham or actual stress or trauma. The animals were sacrificed at various times postinsult and the ceca, mesenteric lymph nodes (MLN), spleens, and livers were quantitatively cultured. Neither the incidence nor the magnitude of bacterial translocation was increased in the cold-exposed animals compared to control mice. The incidence of bacterial translocation to the systemic organs was higher in the animals with a normal flora receiving femoral fracture amputation (11%) (P less than 0.02) than in animals receiving a thermal injury (1%) or sham-injured control mice (0%). In contrast, the incidence of translocation to the liver or spleen was higher in burned mice monoassociated with E. coli C-25 (60%) (P less than 0.01) than in E. coli monoassociated mice sustaining femoral fracture amputation (17%). Stress alone (cold exposure) does not promote bacterial translocation; however, trauma, especially in combination with retained necrotic tissue, promotes bacterial translocation. Thus bacteria colonizing the gut can invade systemic organs after trauma, especially when the normal ecology of the gut flora has been disrupted.     

A model of bacterial translocation in neuroblastoma-bearing mice

PURPOSE: The aim of this study was to establish a model of bacterial translocation (BT) in neuroblastoma-bearing mice. METHODS: A suspension of 1 x 10(6) cells of the murine neuroblastoma cell line C1300 was injected subcutaneously into the thighs of 8-week-old female A/J mice, which were then killed after 7, 14, and 21 days. Some of the mice were given 1-microm or 2-microm fluorescein-labeled latex beads in their drinking water for 7 days before being killed. Mesenteric lymph nodes (MLNs) were aseptically removed and cultured for 72 hours at 37 degrees C. Segments of distal ileum were obtained for histologic examination. Samples of venous blood were obtained for laboratory tests. RESULTS: Tumors were found at the injection sites on days 14 and 21 after C1300 injection. Although tumors were not found in 7 days, significantly high number of 1-microm latex beads were detected in MLNs compared with the control, and the number increased with tumor growth. The number of 2-microm latex beads was significantly higher on days 14 and 21. The percentage of mice with MLN cultures positive were significantly higher on day 14, and the percentage increased along with tumor growth. On day 21 after C1300 injection, body weight loss and anemia were observed, and histologic findings of the terminal ileum showed mucosal edema and villous thinning. Serum levels of interleukin (IL)-6 were significantly higher in mice killed 14 and 21 days after injection. CONCLUSIONS: The results suggest that BT from the gut to MLNs may occur in neuroblastoma C1300-bearing mice, and it increases along with tumor growth. Even in the early stage of malignancy, particles as small as 1 microm may translocate from the gut to MLNs.     

Value of distal colon washout in civilian rectal trauma--reducing gut bacterial translocation

Recent experience with civilian rectal trauma challenges the military dictum advocating routine distal colon washout. Opponents contend that septic morbidity is not influenced by perioperative removal of feces from the rectosigmoid region. In an effort to elucidate this issue, we reviewed 27 consecutive patients sustaining extraperitoneal rectal trauma over the past 5 years. One patient, exsanguinating from abdominal vascular injury, was excluded from further analysis. In the remaining 26 patients, rectal injury was due to gunshot wound in 16 (62%), pelvic fracture in 8 (31%), and stab wound in 2 (7%). The mean Revised Trauma Score was 6.9 +/- 0.4, Abdominal Trauma Index 20.9 +/- 8.1, and Injury Severity Score 28.6 +/- 11.0. Proximal colostomy was done in all patients and presacral drains were placed in 23 (88%). Broad-spectrum antibiotics were administered for a minimum of 5 days. Thirteen (50%) of the group underwent intraoperative washout of the distal rectosigmoid colon, dictated by attending surgeon's preference; the other half did not. These two groups were otherwise comparable with respect to injury mechanism, shock on arrival, rectal wound severity, associated injuries, and perioperative blood transfusions. Major complications were greater in the no-washout versus washout groups: pelvic abscess, 46% vs. 8%; rectal fistulae, 23% vs. 8%; and sepsis, 15% vs. 8%. The single death (4%) occurred in the no-washout group. Although based on a small group of patients, these trends imply that distal colon washout reduces septic morbidity following civilian rectal trauma.(ABSTRACT TRUNCATED AT 250 WORDS)     

创伤及休克肠道细菌移位的研究

研究创伤失血性休克肠道细菌移位的发生率。设计兔创伤失血性休克试验模型，实验组３０只兔，腹部皮肤撕脱１００ｍｍ×９０ｍｍ，并行股动脉放血致休克，对照组１０只兔，腹部撕脱同实验组，不放血致休克。对照组术后１小时、３小时、５小时取标本均未发现肠道细菌移位，实验组术后１小时采标本已有肠道细菌移位，３小时、５小时组细菌移位达３０％。认为创伤失血性休克早期即有肠道细菌移位，并讨论了其临床意义     

The effect of surgical trauma on the bacterial translocation from the gut.

Bacterial translocation is the passage of viable bacteria from the lumen of the gastrointestinal tract through the intestinal mucosa to other sites. It is believed that bacterial translocation may lead to infection and septicemia. The purpose of this study was to determine what factors in experimental surgical trauma lead to bacterial translocation. Two-month-old Wistar albino rats were divided into five groups: (A) control; (B) anesthesia (ether inhalation); (C) anesthesia and surgery (median laparotomy and transient compression of the intestines); (D) fasting only; and (E) anesthesia, surgery, and fasting. After 48 hours, ileum, mesenteric lymph nodes, and blood were cultured for aerobic and anaerobic organisms. In each group the number of animals with bacteria overgrowth was calculated. The incidence of bacterial translocation to mesenteric lymph nodes and blood in groups B and D were similar to the controls (P greater than .01). There was a significant increase in the number of animals with bacterial translocation in groups C and E (P less than .001). The majority of translocating bacteria were E coli.     

Effect of oral antibiotics and bacterial overgrowth on the translocation of the GI tract microflora in burned rats

Infections in burned patients have generally been considered to arise from exogenous organisms. Consequently, the therapy of burned patients has emphasized the use of infection control policies and topical antimicrobial agents to reduce bacterial colonization. Even though enteric bacteria are frequently found in the burn wound little attention has been paid to the patient's own GI tract microflora as a potential source of organisms colonizing the burn wound. The current experiments were carried out to determine if the bacteria present in the GI tract of healthy animals would penetrate (translocate) through the GI mucosa and spread to visceral organs after a moderate or major thermal injury. The results of these experiments indicated that bacteria can translocate across the wall of the GI tract and survive in the mesenteric lymph nodes in healthy rats. Furthermore, when the GI tract microflora is altered, either due to bacterial overgrowth or under the influence of oral antibiotic therapy, not only will bacteria translocate to the mesenteric lymph nodes but bacteria will also spread to other visceral organs. The results of these experiments support the hypothesis that the GI tract can serve as a reservoir for nosocomial infections in the burned patient, since bacteria can translocate across the mucosal barrier of the GI tract after thermal injury and survive in visceral organs before colonization of the burn wound occurs.     

Role of bacterial adherence and the mucus barrier on bacterial translocation: effects of protein malnutrition and endotoxin in rats.

OBJECTIVE: The purpose of the study was to investigate the potential relations between mucosal bacterial adherence, intestinal mucus and mucin content, and bacterial translocation. SUMMARY BACKGROUND DATA: The attachment of bacteria to mucosal surfaces is the initial event in the pathogenesis of most bacterial infections that originate at mucosal surfaces, such as the gut. The intestinal mucus layer appears to function as a defensive barrier limiting micro-organisms present in the intestinal lumen from colonizing enterocytes. Consequently, studies focusing on the biology of bacterial adherence to the intestinal mucosa likely are to be important in clarifying the pathogenesis of gut origin sepsis. METHODS: To explore the relations between intestinal bacterial adherence, mucus bacterial binding, and bacterial translocation, two models were used. One (protein malnutrition) in which profound alterations in intestinal morphology occurs in the absence of significant translocation and one (endotoxin challenge) in which bacterial translocation occurs and intestinal morphology is relatively normal. RESULTS: Protein malnutrition was not associated with bacterial translocation and measurement of enteroadherent, mucosally associated bacterial population levels documented that the total number of gram-negative enteric bacilli adherent to the ileum and cecum was less in the protein-malnourished rats than in the normally nourished animals (p < 0.01). Furthermore, there was an inverse relation between the duration of protein malnutrition and bacterial adherence to the intestinal mucosa (r = 0.62, p < 0.002). In contrast, after endotoxin challenge, the level of enteroadherent bacteria was increased and bacterial translocation was observed. The binding of Escherichia coli to immobilized ileal mucus in vitro was decreased significantly in protein-malnourished rats, whereas E. coli binding to insoluble ileal mucus was increased in the rats receiving endotoxin. CONCLUSIONS: This study indicates that the adherence of bacteria to the intestinal mucosal surface is an important factor in bacterial translocation, that intestinal mucus modulates bacterial adherence, and that increased levels of mucosally associated bacteria are associated with a loss intestinal barrier function to bacteria.