Postinduction bacteremia in experimental acute pancreatitis

Bacterial translocation in acute pancreatitis

Bacterial translocation is a phenomenon in which live bacteria or their products cross the intestinal barrier to other organs or the circulatory system. Gut translocation of bacteria has been reported in both animal models, and clinical trials often accompany acute pancreatitis and are believed to be linked to patient outcome, especially in severe acute pancreatitis. Therefore, the mechanisms of intestinal bacterial translocation in acute pancreatitis have become a topic of interest in recent years. This review discusses Bacterial translocation in acute pancreatitis, identifies possible mechanisms of action, and provides an overview of the methods used to detect Bacterial translocation in acute pancreatitis. This review also highlights areas that require further research.

The Effects of Total Colectomy on Bacterial Translocation in a Model of Acute Pancreatitis

Prevention of secondary infection is currently the main goal of treatment for acute necrotizing pancreatitis. Colon was considered as the main origin of secondary infection. Our aim was to investigate whether prophylactic total colectomy would reduce the rate of bacterial translocation and infection of pancreatic necrosis. Forty-two Sprague-Dawley rats were used. Pancreatitis was created by ductal infusion of sodium taurocholate. Rats were divided into four groups: group-1, laparotomy + pancreatic ductal infusion of saline; group-2, laparotomy + pancreatic ductal infusion of sodium taurocholate; group-3, total colectomy + pancreatic ductal infusion of saline; and group-4, total colectomy + pancreatic ductal infusion of sodium taurocholate. Forty-eight hours later, tissue and blood samples were collected for microbiological and histopathological analysis. Total colectomy caused small bowel bacterial overgrowth with gram-negative and gram-positive microorganisms. Bacterial count of gram-negative rods in the small intestine and pancreatic tissue in rats with colectomy and acute pancreatitis were significantly higher than in rats with acute pancreatitis only (group-2 versus group-4; small bowel, p = <0.001; pancreas, p = 0.002). Significant correlation was found between proximal small bowel bacterial overgrowth and pancreatic infection (r = 0,836, p = 0.001). In acute pancreatitis, prophylactic total colectomy (which can mimic colonic cleansing and reduction of colonic flora) induces small bowel bacterial overgrowth, which is associated with increased bacterial translocation to the pancreas.

The use of animal models to study bacterial translocation during acute pancreatitis

Infection of pancreatic necrosis with intestinal flora is accepted to be a main predictor of outcome during severe acute pancreatitis. Bacterial translocation is the process whereby luminal bacteria migrate to extraintestinal sites. Animal models were proven indispensable in detecting three major aspects of bacterial translocation: small bowel bacterial overgrowth, mucosal barrier failure, and disturbed immune responses. Despite the progress made in the knowledge of bacterial translocation, the exact mechanism, origin and route of bacteria, and the optimal prophylactic and treatment strategies remain unclear. Methodological restrictions of animal models are likely to be the cause of this uncertainty. A literature review of animal models used to study bacterial translocation during acute pancreatitis demonstrates that many experimental techniques per se interfere with intestinal flora, mucosal barrier function, or immune response. Interference with these major aspects of bacterial translocation complicates interpretation of study results. This paper addresses these and other issues of animal models most frequently used to study bacterial translocation during acute pancreatitis.

Acute lung injury in two experimental models of acute pancreatitis: infusion of saline or sodium taurocholate into the pancreatic duct

OBJECTIVE

To compare acute pulmonary changes secondary to sodium taurocholate hemorrhagic pancreatitis with those changes secondary to a less severe pancreatitis induced by saline infusion into the biliopancreatic duct.

DESIGN

Prospective, randomized controlled trial.

SETTING

University pulmonary laboratory.

SUBJECTS

A total of 110 male Wistar rats.

INTERVENTIONS

Pancreatitis was induced by either 0.5 mL of a 4% solution of sodium taurocholate (TAU group) or 0.5 mL of normal saline (SAL group) injection into the biliopancreatic duct. Data were compared with data from control (sham-operated) animals (SHAM group).

MEASUREMENTS AND MAIN RESULTS

The severity of pancreatic and pulmonary injuries was evaluated 1, 3, and 8 days after the induction of acute pancreatitis by morphometric and pulmonary mechanical studies. Biliopancreatic duct pressure was measured during infusion of solutions in SAL and TAU groups. SAL and TAU groups developed an intense necrohemorrhagic pancreatitis on day 1 without differences in biliopancreatic duct pressures (134.0+/-45.1 cm H2O vs. 123.3+/-23.4 cm H2O). Acute pancreatic lesions were still intense on day 3 in the TAU group only. Pulmonary resistance in SAL and TAU groups was significantly greater than in the SHAM group on day 3 only. On day 1, there was an increase in intraalveolar edema in both groups (p < .02). There was an increase in polymorphonuclear cells in alveolar septa on day 1 only in the TAU group (p < .001). In contrast, both experimental groups presented greater values of PMN cells on day 8 compared with the SHAM group (p < .001). Both groups with pancreatitis showed an increase in alveolar distention and collapse on day 1 that persisted only in the TAU group on days 3 and 8. No deaths were observed in the control (SHAM) group. In contrast, the SAL group had lower mortality than the TAU group in the first two days (17% and 52%, respectively, p = .03).

CONCLUSION

High-pressure infusion of normal saline into the biliopancreatic duct of rats results in significant pancreatic and lung alterations. These changes are worse in the presence of sodium taurocholate.

Pancreatic phospholipase A2 induces bacterial translocation in rats

The importance of pancreatic enzymes, particularly phospholipase A2 (PLA2), for bacterial translocation, which is considered to be one of the aggravating causes of acute pancreatitis, was investigated. Male rats were administered an intraperitoneal or intravenous injection of normal saline, PLA2, or amylase. Four days later, the mesenteric lymph nodes (MLNs) and portal blood of the animals were cultured. None of the animals had a positive portal blood culture. The MLNs contained enteric bacteria in 78% of the animals given 50 mg/kg of PLA2 intraperitoneally. 5 mg/kg of PLA2 intraperitoneally, 50 mg/kg of amylase intraperitoneally, or 50 mg/kg of PLA2 intravenously showed positive cultures in 25%, 20%, and 11%, respectively. None of the animals given intraperitoneal or intravenous normal saline had positive cultures of their MLNs. Intraperitoneal injection of 25 mg/kg of nafamostat mesilate just before intraperitoneal PLA2 (50 mg/kg) resulted in a reduction of positive MLNs from 70% to 30%. The cecal myeroperoxidase (MPO) activity of animals administered 50 mg/kg of PLA2 intraperitoneally was significantly higher compared with animals administered saline intraperitoneally. These results indicate that intraperitoneal leakage of PLA2 plays an important role in bacterial translocation during acute pancreatitis and that administration of a protease inhibitor may be effective against the bacterial translocation.

Controlled clinical trial of selective decontamination for the treatment of severe acute pancreatitis

OBJECTIVE

A randomized, controlled, multicenter trial was undertaken in 102 patients with objective evidence of severe acute pancreatitis to evaluate whether selective decontamination reduces mortality.

SUMMARY BACKGROUND DATA

Secondary pancreatic infection is the major cause of death in patients with acute necrotizing pancreatitis. Controlled clinical trials to study the effect of selective decontamination in such patients are not available.

METHODS

Between April 22, 1990 and April 19, 1993, 102 patients with severe acute pancreatitis were admitted to 16 participating hospitals. Patients were entered into the study if severe acute pancreatitis was indicated, on admission, by multiple laboratory criteria (Imrie score > or = 3) and/or computed tomography criteria (Balthazar grade D or E). Patients were randomly assigned to receive standard treatment (control group) or standard treatment plus selective decontamination (norfloxacin, colistin, amphotericin; selective decontamination group). All patients received full supportive treatment, and surveillance cultures were taken in both groups.

RESULTS

Fifty patients were assigned to the selective decontamination group and 52 were assigned to the control group. There were 18 deaths in the control group (35%), compared with 11 deaths (22%) in the selective decontamination group (adjusted for Imrie score and Balthazar grade: p = 0.048). This difference was mainly caused by a reduction of late mortality (> 2 weeks) due to significant reduction of gram-negative pancreatic infection (p = 0.003). The average number of laparotomies per patient was reduced in patients treated with selective decontamination (p < 0.05). Failure of selective decontamination to prevent secondary gram-negative pancreatic infection with subsequent death was seen in only three patients (6%) and transient gram-negative pancreatic infection was seen in one (2%). In both groups of patients, all gram-negative aerobic pancreatic infection was preceded by colonization of the digestive tract by the same bacteria.

CONCLUSION

Reduction of gram-negative colonization of the digestive tract, preventing subsequent pancreatic infection by means of selective decontamination, significantly reduces morbidity and mortality in patients with severe acute necrotizing pancreatitis.

Role of platelet activating factor in acute pancreatitis induced by lipopolysaccharides in rabbits

In the present study we demonstrated that a single injection of endotoxin (lipopolysaccharides, E. Coli 0111-B4) into the superior pancreaticoduodenal artery of rabbits induced a dose-dependent acute necrotizing pancreatitis. The lesions observed by light microscopy were significant for 10 micrograms lipopolysaccharides and were maximal for 20 micrograms. After 24 h the main findings were edema, acinar cell vacuolisation, polymorphonuclear neutrophil infiltration and tissue necrosis. The pancreatic lesions developed strictly in the area supplied by the artery injected with lipopolysaccharides, without significant intestinal involvement. Since platelet-activating factor (1-O-hexadecyl-2-acetyl-sn-glycero-3- phosphocholine, PAF; 50-500 ng), a phospholipid mediator of endotoxin-induced inflammation and shock, was previously shown to cause an acute necrotizing pancreatitis in rabbits, the role of PAF in the development of acute pancreatitis induced by lipopolysaccharides was studied by evaluating: (1) the synergism between doses of lipopolysaccharides (5-10 micrograms), which produced a mild tissue injury, and doses of PAF (10 ng) not producing, per se, any significant injury, and (2) the effect of three structurally unrelated PAF receptor antagonists. The results obtained demonstrated that 10 ng of PAF significantly potentiated pancreatic tissue damage induced by 10 micrograms of lipopolysaccharides.(ABSTRACT TRUNCATED AT 250 WORDS)

Pathogenesis of pancreatic sepsis

Although pancreatic sepsis is the most common cause of major morbidity and mortality associated with acute pancreatitis, the pathogenesis of such infections is unknown. Since intraperitoneal foci of inflammation are known to promote bacterial translocation, we hypothesized that acute pancreatitis promotes bacterial translocation that leads to infection of the inflamed pancreas and peripancreatic tissues. Non-lethal acute pancreatitis was induced in rats, and the translocation of live bacteria to the pancreas, mesenteric lymph nodes, liver, and spleen was determined. The presence of orally fed fluorescent beads, sensitive inert markers of translocation, was also determined in the pancreas and mesenteric lymph nodes. Live bacteria were recovered from 33% of the pancreata of rats with acute pancreatitis but from none of the control rats. Beads were visualized in 91% of the pancreata of rats with acute pancreatitis but in none of the pancreata from control rats. Beads were not visualized in the mesenteric lymph nodes of rats with acute pancreatitis, suggesting a transperitoneal route of migration. We conclude that acute pancreatitis promotes bacterial translocation leading to transperitoneal infection of the pancreas. These results support the use of selective decontamination of the gut and peritoneal lavage for the prevention of pancreatic infections in acute pancreatitis.

Role of bacterial infection in diet-induced acute pancreatitis in mice

This study was performed to elucidate the role of bacterial infection in acute pancreatitis in young female mice fed a choline-deficient diet supplemented with 0.5% DL-ethionine (CDE diet). Mice were randomly classified into two groups: one had been fed CDE diet alone (nonantibiotic group), the other was fed a CDE diet with oral administration of antibiotics (antibiotic group). Survival rates at 96 and 144 h after introduction of the CDE diet were significantly improved in the antibiotic group, 25.0 and 19.4%, respectively, as compared with 3.6 and 0% in the nonantibiotic group (p, 0.05). Aerobic and anaerobic bacterial cultures of blood, ascites, spleen, and pancreas were taken from living mice 72 h after introduction of the CDE diet. Positive bacterial growth from one or more of the specimens occurred in 29.4% of the nonantibiotic group, and in 10.0% of the antibiotic group. Mice with pancreatic necrosis had a higher positive culture rate, 62.5% in the nonantibiotic group vs 20.0% in the antibiotic group. These results suggest that reduction of intestinal flora in mice inhibits secondary infection caused by bacterial translocation and improves survival in diet-induced hemorrhagic pancreatitis. We believe the development of bacterial infection of gut origin may be a factor influencing mortality in severe pancreatitis.

Bacterial infection is not necessary for lethal necrotizing pancreatitis in mice

Sepsis is the most common cause of late death in pancreatitis. The presence of early bacterial infection has been correlated with the severity of the disease. A choline-deficient ethionine-supplemented (CDE) diet given to young female mice produces severe necrotizing pancreatitis that has morphologic and biochemical similarities to the human disease. We therefore searched for bacterial pancreatic infection in female CD-1 mice given the CDE diet. The mortality rate was 47.5% in mice fed the CDE diet. All of these mice had severe pancreatitis with inflammation, edema, and necrosis on histologic examination. Bacterial infection was present in 1/12 pancreatica among nonsurvivors and in 1/32 pancreatica in surviving animals (p not significant). Histologic examination showed edema to be more pronounced in surviving mice, although the overall severity of morphologic changes was not significantly different between survivors and nonsurvivors. We conclude that bacterial infection is not a determinant of the severity or lethality of experimental pancreatitis induced by the CDE diet.

Bacterial contamination of pancreatic necrosis. A prospective clinical study

In a prospective clinical study including 114 patients with acute necrotizing pancreatitis, but excluding patients with a pancreatic abscess, necrotic material obtained at surgery was tested bacteriologically. Intestinal microorganisms were cultured in 39.4% of the cases. The contamination rate was 23.8% in patients operated on during the first 7 days of the attack; it rose to 71.4% in the third week and decreased to 32.5% after the fourth week. Intra- and extrapancreatic necrosis was more widespread and pancreatitis-associated ascites was more frequent in patients with proven contamination. The number of objective signs was 4.5 (median) and postoperative mortality was 37.8% in bacteriologically positive subjects, whereas the number was 3.5 (median) and mortality was 8.7% in bacteriologically negative patients. Morphologic and clinical alterations were more severe, and the mortality rate was significantly elevated, in patients with a short history of disease and bacterial contamination of necrotic tissue. All 5 patients with pancreatic sepsis who were operated on in the first 7 days of the disease, as compared with 2 of 16 patients with sterile necrosis, died. Thus, it is demonstrated that bacterial contamination of pancreatic necrosis occurs early and frequently, causing a significant increase in morbidity and mortality, particularly when it develops in the initial stages of the attack.

Early increase in intestinal permeability in patients with severe acute pancreatitis: correlation with endotoxemia, organ failure, and mortality

Sepsis accounts for 80% of deaths from acute pancreatitis. This study aimed to investigate early changes in intestinal permeability in patients with acute pancreatitis, and to correlate these changes with subsequent disease severity and endotoxemia. The renal excretion of enterally administered polyethylene glycol (PEG) 3350 and PEG 400 was measured within 72 hours of onset of acute pancreatitis to determine intestinal permeability. Severity was assessed on the basis of APACHE II scores and C-reactive protein measurements. Serum endotoxin and antiendotoxin antibodies were measured on admission. Eight-five patients with acute pancreatitis (mild in 56, severe in 29) and 25 healthy control subjects were studied. Urinary excretion of PEG 3350 (median) was significantly greater in patients who had severe attacks (0.61%) compared to those with mild disease (0.09%) and health control subjects (0.12%) (P <0. 0001), as was the permeability index (PEG 3350/400 excretion) (P <0. 00001). The permeability index was significantly greater in patients who subsequently developed multiple organ system failure and/or died compared with other severe cases (0.16 vs. 0.04) (P = 0.0005). The excretion of PEG 3350 correlated strongly with endotoxemia (r = 0.8; P = 0.002). Early increased intestinal permeability may play an important role in the pathophysiology of severe acute pancreatitis. Therapies that aim to restore intestinal barrier function may improve outcome.