Rat Model Of Intra-abdominal Sepsis Research Articles

The Effect of Platelet-Rich-Plasma on the Healing of Left Colonic Anastomosis in a Rat Model of Intra-Abdominal Sepsis

ABSTRACTObjective: The aim of this study was to investigate the effect of platelet-rich plasma (PRP) on the healing of colonic anastomosis in the presence of sepsis. Materials and Method: Fifty Wistar-albino male rats were used. Ten healthy rats were euthanized to prepare PRP, the rest were subjected to colonic anastomosis and randomly allocated into four groups of 10 rats each as anastomosis without PRP (C), without PRP in sepsis (SC), anastomosis with PRP (C-PRP), and with PRP in sepsis (S-PRP). Sepsis was induced by cecal ligation and puncture procedure. All animals were euthanized on postoperative day 7. The body weight change, anastomotic bursting pressure (ABP), tissue hydroxyproline (TH) and histopathological examination of each group were analyzed by using one-way analysis of variance (ANOWA) and Tukey's HSD post-hoc test to assess the differences between the groups. Results: There was no statistical difference among the groups in terms of body weight changes. The ABP was measured at a mean value of 179.5 ± 10.3, 129.3 ± 14.2, 209 ± 14.4, and 167.5 ± 7.5 mm-Hg, in group C, SC, C-PRP, and S-PRP, respectively. The ABP and TH of C-PRP group was significantly higher than three groups (p < .05, for each comparison). In sepsis, PRP significantly raised the mean ABP and TH levels up to the levels of C group. Tissue regeneration was significant with increased collagen formation in C-PRP group than the other groups (p < .05). The healing effect of PRP in the presence of sepsis was significant than S-group (p < .05), while similar to C group (p = .181). Conclusion: PRP application to colonic anastomosis promotes the healing process in rats with intra-abdominal sepsis.

The protective effects of IgM-enriched immunoglobulin and erythropoietin on the lung and small intestine tissues of rats with induced sepsis: Biochemical and histopathological evaluation

Context: Sepsis continues to be a significant problem for critical care patients.Objective: To evaluate the protective effects of IgM-enriched immunoglobulin and erythropoietin on pulmonary and small intestine tissues in a rat model of intra-abdominal sepsis induced via the cecal ligation and puncture (CLP) method.Materials and methods: Male Sprague–Dawley rats were used. Control group (n = 6): surgical procedure was not performed. Laparotomy was only performed in the sham group (n = 6) and CLP was only performed in the sepsis (CLP) group (n = 30). After erythropoietin (2000 U/kg, intraperitoneal) was given in the sepsis + erythropoietin (CLP + EPO) group (n = 30), IgM-enriched immunoglobulin (600 mg/kg, intraperitoneal) was given in the sepsis + pentaglobin (CLP + PEN) group (n = 30), CLP was created. Intracardiac blood samples were collected for biochemical analysis; lung and small intestine tissue samples were removed for histopathological evaluation.Results: Plasma TNF-α levels (pg/ml) were similar among CLP, CLP + EPO, and CLP + PEN groups (204.0 ± 52.4, 198.5 ± 17.3, and 214.6 ± 93.6, respectively). The CLP group had higher plasma IL-1β levels (pg/ml) compared with CLP + EPO and CLP + PEN groups (325.1 ± 134.1, 164.3 ± 25.6, and 186.3 ± 26.0, respectively) (p < 0.05). Rats in CLP + EPO and CLP + PEN groups had abolished histopathologic appearance of lung and small intestine tissues compared with rats in the CLP group.Discussion and conclusion: Our findings support the use of EPO and IgM-enriched immunoglobulin in the prevention of lung and small intestine injuries associated with sepsis.

The Effects of Dexmedetomidine on Secondary Acute Lung and Kidney Injuries in the Rat Model of Intra-Abdominal Sepsis

In the present study, the effects of dexmedetomidine on secondary lung and kidney injuries were studied in the rat model of intra-abdominal sepsis by immunohistological and biochemical examinations. We measured serum creatinine, kidney tissue malondialdehide and plasma neutrophil gelatinase-associated lipocalin levels. In order to evaluate tissue injury we determined kidney tissue mononuclear cell infiltration score, alveolar macrophage count, histological kidney and lung injury scores and kidney and lung tissue immunoreactivity scores. We demonstrated that dexmedetomidine attenuates sepsis-induced lung and kidney injuries and apoptosis in the rat model of sepsis. There is still need for comparative studies in order to determine the effects of dexmedetomidine on organ functions in early human sepsis.

Effect of therapeutic hypothermia according to severity of sepsis in a septic rat model

Aim of studyThe effects of therapeutic hypothermia (HT) during experimental sepsis may be influenced by disease severity. We experimentally investigated the effect of therapeutic HT on varying disease severity in a septic rat model. Materials and methodsAn adult male Sprague-Dawley rat model of intra-abdominal sepsis was used. To modify the disease severity, we used two different models; a moderate severe sepsis model (MSSM) and a severe septic shock model (SSSM). All rats were randomized to a hypothermia group (HT, 30–32°C) or a normothermia group (NT, 36–38°C) 1h after sepsis induction in each model. HT was maintained for 4h and rewarming was conducted for 2h. Survival time was recorded for up to 12h in the SSSM group and 24h in the MSSM group. Acute lung and liver injury, cytokine, and malondialdehyde (MDA) levels were investigated 7h after sepsis induction. Hemodynamic profiles were also evaluated. ResultsIn the SSSM, there were survival benefits and reduced acute lung and liver injury with therapeutic HT. Therapeutic HT was also associated with significantly reduced levels of plasma interleukin-6 and tissue malondialdehyde (MDA) levels in the liver and lung compared with the NT group in the SSSM. There was a tendency for the mean arterial pressure to be higher in the HT group compared to the NT group in the SSSM. In MSSM, however, there was no such beneficial effect. ConclusionIn this rat model of severe septic shock, therapeutic HT showed beneficial effects. In contrast, therapeutic HT did not show protective effect in the moderate sepsis model.

Combination of Fibrin Glue with Growth Hormone Augments Healing of Incomplete Intestinal Anastomoses in a Rat Model of Intra-Abdominal Sepsis: A Dynamic Study

This study was devised to investigate whether fibrin glue (FG) in combination with growth hormone (GH) could have a beneficial effect at a late period (14 days) after injury. Male Wistar rats, with abdominal sepsis induced by an incomplete anastomosis, were divided into three groups. In the control group, the rats got incomplete anastomoses sutured alone; in the FG and FG/GH groups, anastomoses protection was performed with application of FG alone or in combination with GH. The anastomotic bursting pressure (ABP) was significantly higher in the FG/GH group than that of the FG group on postoperative day (POD) 5 (p <. 01), while it could not be measured from POD 7 to POD 14 because of intestinal dehiscence. There was no difference between FG and FG/GH group on POD 3 and POD 5 in anastomotic tensile strength, which was significantly higher in the FG/GH group than that of the FG group from POD 7 to POD 14 (p <. 001). Hydroxyproline content of the FG/GH group was significantly higher than that of the control from POD 3 and that of the FG group from POD 5 (p <. 05). Combination of FG with GH had a synergistic effect to improve intestinal anastomotic healing over a limited 14-day course of observation.

Effect of the Combination of Fibrin Glue and Growth Hormone on Incomplete Intestinal Anastomoses in a Rat Model of Intra-Abdominal Sepsis

The presence of established intra-abdominal sepsis has been considered a contraindication to primary anastomoses. Our hypothesis was that fibrin glue (FG), growth hormone (rhGH), and combination of them synergistically improve intestinal primary anastomotic healing in a rat model of intestinal fistulae with peritonitis. Male Wistar rats, induced intestinal fistulae with peritonitis after 24 h, were performed an enterectomy and intestinal anastomoses. Group A, rats (n = 60) had a complete anastomoses (end-to-end single layer anastomoses using 12 inverted interrupted 6-0 sutures) without peritonitis, group B, rats (n = 60) had a complete anastomoses after 24 h of peritonitis, group C rats had an incomplete anastomoses (four inverted interrupted sutures), groups D, E, F rats (n = 60) received FG, rhGH, or both of them, respectively. rhGH was given daily for 5 days. Anastomoses indicated the anastomotic bursting pressure (ABP), tensile strength, and hydroxyproline content, were determined. On POD 1, ABP of group C and group D was significantly lower than that of other groups (P < 0.01); On POD 3, ABP could not be determined because of intestinal dehiscence in groups C and E, ABP was significantly higher in groups D and F than that of groups A and B (P < 0.01); the ABP increased after 5 days of operation in groups A, B, and F. At the same time, that of group D decreased (P < 0.01). On POD 5, the tensile strength was significantly higher in groups A, D, and F than that in groups C, and E. On POD 5, hydroxyproline content was higher in groups D and F compared to that in group C (P < 0.05). These data suggested that FG improve intestinal primary anastomotic healing within post-operative 5 days in a rat model of intestinal fistulae with peritonitis. RhGH alone fails to improve intestinal anastomotic healing, and the combination of FG and rhGH have no synergistic effect to improves intestinal anastomotic healing.

Efficacy of moxifloxacin monotherapy versusgatifloxacin monotherapy, piperacillin-tazobactam combination therapy, and lindamycin plus gentamicin combination therapy: An experimental study in a rat model of intra-abdominal sepsis induced by fluoroquinolone-resistant Bacteroides fragilis

Background: In intra-abdominal infections, the activity of antimicrobial agents against Bacteroides fragilis and phenotypically related organisms, and the increasing resistance of these organisms, are of particular importance and concern to surgeons. In vitro data suggest that moxifloxacin is more active than other quinolones against obligately anaerobic organisms, including Bacteroides spp. Objective: The aim of this study was to compare the efficacy of moxifloxacin monotherapy versus gatifloxacin monotherapy and 2 combination therapies (piperacillin-tazobactam and clindamycin plus gentamicin) in a rat model of intra-abdominal sepsis. The end point was marked by the incidence of mortality and intra-abdominal abscesses at necropsy 7 days after bacterial challenge. Methods: Three different strains of B fragilis with different degrees of resistanceto moxifloxacin (minimum inhibitory concentrations [MICs]: 4, 8, and 16 pg/mL) were added to the challenge inoculum in 3 separate experiments. Groups of 20 animals were used in each experiment. Group 1 served as saline-treated controls; group 2 received moxifloxacin 15 mg QD; group 3 received gatifloxacin 25 mg QD; group 4 received piperacillin-tazobactam 93 mg (−83 mg of piperacillin) QD; and group 5 received a combination of clindamycin 15 mg TID plus gentamicin 2 mg TID. All treatments were given intramuscularly. For all antimicrobials, dose was based on peak and trough serum drug concentrations determined by prior testing, with animal doses adjusted based on the ratio of body surface area to body weight, and comparing these doses and levels with studies in humans. Results: In all 3 experiments, the mortality rate with moxifloxacin was significantlylower or statistically similar compared with antibiotic active comparators ( P ≤ 0.024). In addition, there were no significant differences in the incidence of abscess with moxifloxacin versus its comparators or between the 3 moxifloxacin groups across experiments. The best results for moxifloxacin were found in the experiment in which the B fragilis strain with MIC 16 μg/mL was added to the inoculum. Conclusion: The results of this study in an animal model of intra-abdominalsepsis induced by fluoroquinolone-resistant B fragilis suggest that moxifloxacin monotherapy performs as well as combination regimens such as piperacillin-tazobactam and clindamycin plus gentamicin, and is as effective as other fluoroquinolones with antianaerobic activity, such as gatifloxacin.

Efficacy of moxifloxacin monotherapy versusgatifloxacin monotherapy, piperacillin-tazobactam combination therapy, and lindamycin plus gentamicin combination therapy: An experimental study in a rat model of intra-abdominal sepsis induced by fluoroquinolone-resistant

Efficacy of moxifloxacin monotherapy versusgatifloxacin monotherapy, piperacillin-tazobactam combination therapy, and lindamycin plus gentamicin combination therapy: An experimental study in a rat model of intra-abdominal sepsis induced by fluoroquinolone-resistant

Effects of G-CSF and antibiotic prophylaxis in a 2 x 2 factorial design on outcome in septic rats.

In a recently completed randomised clinical trial in patients with colorectal cancer resections the combination of the granulocyte-colony stimulating factor (G-CSF) + cefuroxime/ metronidazole (cef/met) was superior to ofloxacin/metronidazole (ofl/met). These combinations were used to confirm the clinical data and to validate the concept of clinic modelling randomised trials (CMRTs) in a rat model of intra-abdominal sepsis. 80 male Wistar rats were randomised in a 2 x 2 factorial study design. All animals (n = 20/group) received anaesthesia, antihistamines, antibiotic prophylaxis, peritoneal contamination and infection. Groups were: 1) G-CSF + cef/met; 2) placebo + cef/ met; 3) G-CSF+ofl/met; 4) placebo + ofl/met. G-CSF (20 g/kg) prophylaxis was applied three times. Survival at 120 h was analysed with the Kaplan Meier method. Survival rate was best in the G-CSF + cef/met group with 75% and was significantly improved compared to the cef/met placebo group, in which only 42% survived (P < 0.05). Survival rate between both G-CSF groups was similar being 75% in the cef/met and 72% in the ofl/met group. P = 0.10). Ozone increased TNF-alpha and MIP-2 after infection: 127 +/- 23 pg/ml and 94 +/- 19 pg/ml (control group: 398 pg/ml and 369 pg/ml; P < 0.002 and P < 0.01). IL-6 levels were similar in both groups. The results of this CMRT confirmed the result of our clinical G-CSF trial in that G-CSF prophylaxis was most efficacious in combination with cef/met to improve the outcome.

Deleterious effects of mild hypothermia in septic rats are ameliorated by granulocyte colony-stimulating factor.

The authors studied the effects of mild hypothermia on the outcome in a rat model of intraabdominal sepsis and tested whether granulocyte colony-stimulating factor (G-CSF) augments the host response and improves outcome during mild hypothermia. A rat model of peritoneal contamination and infection with human stool bacteria was used to simulate clinical trials that included increasing complexity. In trial 1, postoperative hypothermia (32 degrees C) was compared with normothermia (38 degrees C), without supportive treatment (10 rats per group). In trial 2, with a more severe infection, rats were given antibiotic prophylaxis. Using 20 rats per group, the authors compared postoperative hypothermia (32 degrees C), normothermia, and postoperative hypothermia (32 degrees C) with 20 mug/kg G-CSF prophylaxis given 12 h before surgery and 12 h and 36 h after surgery. The primary endpoint was death at 120 h. Secondary endpoints were systemic cytokine concentrations, leukocyte counts, and the phagocytic activity of granulocytes and monocytes. In trial 1, 50% of the normothermia group and 10% of the postoperative hypothermia group survived. In trial 2, 50% of the normothermia group, 20% of the hypothermia group, and 60% of the hypothermia plus G-CSF group survived. Postoperative hypothermia plus G-CSF reduced plasma concentrations of interleukin-6 (hypothermia group, 511 +/- 104 pg/ml; hypothermia plus G-CSF group, 247 +/- 51 pg/ml) and macrophage inflammatory protein-2 (hypothermia group, 239 +/- 43 pg/ml; hypothermia plus G-CSF group, 178 +/- 21 pg/ml). In this rat model of intraabdominal sepsis, postoperative hypothermia was deleterious. However, G-CSF treatment, initiated before contamination, reduced the mortality rate, increased the neutrophil count, and downgraded the systemic cytokine response.

Antimicrobial efficacy testing of moxifloxacin during the peritonitis and abscess formation stages of intra-abdominal sepsis: A controlled trial in the rat model

Background: Moxifloxacin is a fluoroquinolone with a broad range of antimicrobial activity against gram-negative and gram-positive, facultative, and obligately anaerobic bacteria, including certain quinolone-resistant organisms. Objective: Efficacy of moxifloxacin was compared with that of a combination of clindamycin + gentamicin in a rat model of intra-abdominal sepsis, with end points including mortality during the first 2 to 4 days after initiation of sepsis and the incidence of intra-abdominal abscess noted at necropsy. The bacterial challenge was prepared from cecal contents or an enhanced cecal content preparation. Methods: Groups of 20 animals were employed in the first part of the study, which used a cecal content challenge: group 1 served as saline-treated controls; group 2 received moxifloxacin 15 mg once daily; and group 3 received a combination of clindamycin 15 mg TID + gentamicin 2 mg TID. Dosing was determined for all antimicrobial agents based on peak and trough serum levels by prior testing (ie, experiments initiated before this study to determine the appropriate dosage in animals that approximates the levels obtained in humans with the antimicrobial agent under investigation), adjusting doses according to a body surface area/body weight ratio, and comparing these doses and levels with studies in humans. In the second part of the study, moxifloxacin was compared with levofloxacin (both 15 mg once daily) in an enhanced abscess model. Results: The mortality rate was 57.9% in the control group versus 0% in the moxifloxacin group and 5% in the clindamycin + gentamicin group ( P < 0.001 for both treatment groups vs control). The incidence of abscess among survivors was 100% in the control group versus 0% in the moxifloxacin group and 5.3% in the clindamycin + gentamicin group ( P < 0.001 for both vs control). In the Bacteroides fragilis—enhanced abscess model, the incidence of abscess was significantly lower in the moxifloxacin group compared with both the saline-treated controls ( 4 19 [21.1%] vs 5 5 [100%] , respectively; P = 0.003) and the levofloxacin group ( 4 19 [21.1%] vs 11 20 [55%] , respectively; P = 0.042). Conclusions: This study shows that moxifloxacin is as effective as other established therapeutic regimens in reducing the incidence of both mortality and intra-abdominal abscesses in this animal model. In addition, moxifloxacin is extremely effective in preventing abscesses caused by obligate anaerobes, even in an enhanced model for abscess development, and its efficacy is superior to that of levofloxacin.

Comparative efficacy of BMS-284756, a new fluoroquinolone, versus established antimicrobial regimens for the treatment of experimental intra-abdominal sepsis in rats

Background: BMS-284756 is a new des-fluoro-(6)-quinolone with broad anti-microbial activity against gram-negative and gram-positive facultative and obligately anaerobic bacteria, including certain quinolone-resistant organisms. Objective: The purpose of this animal study was to examine the efficacy of BMS-284756 in a rat model of intra-abdominal sepsis. Methods: Five groups of 20 rats each were implanted with a gelatin capsule containing a mixed aerobe/anaerobe inoculum derived from the cecal contents of meat-fed rats. The inoculum was quantitatively and qualitatively examined to ensure that appropriate microbial species were present. Group 1 served as saline-treated controls; Group 2 received BMS-284756, 4 mg/d; Group 3 received BMS-284756, 9 mg/d; Group 4 received ampicillin plus sulbactam 77 mg TID; and Group 5 received a combination of gentamicin 2 mg TID plus clindamycin 15 mg TID. Dosage was determined for all antimicrobial agents based on peak and trough serum levels observed in previous tests, adjusting animal dosages according to a body surface area/body weight ratio and comparing these doses and levels to those from studies in humans. The end points were mortality during the first 2 to 4 days after initiation of sepsis and incidence of intraabdominal abscesses noted at necropsy. Results: The mortality rate was 65% in the control group versus 0% in the treatment groups ( P < 0.001). The incidence of abscess in survivors was 100% in the control group versus 10%, 10%, 5%, and 15% in Groups 2, 3, 4, and 5, respectively ( P < 0.001 vs control), with no significant differences between treatment groups. Conclusions: BMS-284756 is as effective as other established therapeutic regimens in reducing both mortality and the incidence of intra-abdominal abscesses in this animal model. These data suggest that BMS-284756 is an effective treatment for mixed intra-abdominal infections that involve both obligate anaerobes and facultative bacterial species.

Enhancement of peritoneal leukocyte function by granulocyte colony-stimulating factor in rats with abdominal sepsis.

To investigate the therapeutic effects of granulocyte colony-stimulating factor (G-CSF) on the functional activities of circulating and peritoneal neutrophils during intra-abdominal sepsis. Placebo, controlled study, using a rat model of intra-abdominal sepsis. Animal research facility. Male specific pathogen-free Sprague-Dawley rats. Abdominal sepsis was produced in rats by cecal ligation and puncture. The control animals received a sham operation. G-CSF (subcutaneous injection at 50 microg/kg) or vehicle (100 microL of 5% dextrose) treatment was initiated at 1 hr after cecal ligation and puncture or sham operation and repeated at 12-hr intervals thereafter. Six hours after cecal ligation and puncture, CD11b/c and CD18 expression on circulating neutrophils was significantly up-regulated when compared with those in the sham operated control animals. Peritoneal neutrophils exhibited a further up-regulation of these adhesion molecules than did the circulating neutrophils. A sustained up-regulation of CD11b/c and CD18 was found in peritoneal neutrophils even at 24 hrs after cecal ligation and puncture. G-CSF treatment increased CD11b/c expression on circulating neutrophils in 6-hr sham-operated rats, but did not further up-regulate CD11b/c or CD18 expression on circulating or peritoneal neutrophils in cecal ligation and puncture rats. Phagocytic activities of circulating neutrophils assessed by uptake of fluorescent latex microspheres were lower in 24-hr cecal ligation and puncture rats when compared with the sham-operated controls. G-CSF treatment prevented this inhibition. Furthermore, G-CSF enhanced the phagocytic activities of peritoneal neutrophils in both 6- and 24-hr cecal ligation and puncture rats when compared with those of the vehicle-treated animals. Spontaneous hydrogen peroxide generation by circulating neutrophils was increased in 6-hr cecal ligation and puncture rats, but not in 24-hr cecal ligation and puncture rats. Peritoneal neutrophils exhibited an inhibition of phorbol myristate acetate-stimulated hydrogen peroxide generation. G-CSF treatment did not up-regulate neutrophil hydrogen peroxide generation. Circulating and peritoneal neutrophils exhibit marked polymorphism in their functional activities during the host response to abdominal sepsis. G-CSF treatment significantly enhanced the phagocytic function of both circulating and peritoneal neutrophils which may be one mechanism underlying its protective effect in abdominal sepsis.

Prophylaxis with the immunomodulator PGG glucan enhances antibiotic efficacy in rats infected with antibiotic-resistant bacteria.

The emergence of multiple antibiotic-resistant microorganisms has led to a search for alternatives to traditional therapeutic regimens. PGG glucan is a soluble beta-glucan immunomodulator that selectively enhances the microbicidal activities of neutrophils and macrophages without stimulating proinflammatory cytokine production. In the present studies, we examined the ability of PGG glucan to act in concert with antibiotics to decrease mortality in a rat model of intraabdominal sepsis using antibiotic-resistant bacteria as infectious inocula. Results of these studies demonstrated that prophylaxis with PGG glucan in combination with antibiotics provided enhanced protection against lethal challenge with Esherichia coli or Staphylococcus aureus as compared with the use of antibiotics alone.

Dantrolene, an inhibitor of intracellular calcium release, fails to increase survival in a rat model of intra-abdominal sepsis.

Increased release of intracellular calcium has been implicated in cell death and organ failure in endotoxemia and sepsis. We sought to test this hypothesis in a rat model of antibiotic-treated intraperitoneal sepsis with the use of dantrolene sodium, a specific inhibitor of intracellular calcium release. A prospective, randomized controlled trial. An experimental animal laboratory in a university hospital. Two hundred fourteen male Sprague-Dawley rats. Rats were rendered septic by intraperitoneal implantation of sterile feces mixed with live Escherichia coli and allocated to control, vehicle, or dantrolene treatment. A separate group of rats had arterial catheters implanted to allow blood sampling for determination of circulating tumor necrosis factor (TNF)-alpha and lactate concentrations. Additional rats were randomized to receive vehicle or dantrolene after intravenous injection of endotoxin. Over the 7-day study period, survival was significantly worse among rats that received dantrolene at a dose of 10 mg/kg, irrespective of whether treatment was started before or after induction of peritonitis. Mean whole blood lactate for each group peaked at 6 hrs after induction of infection. There were no significant differences in lactate concentration among the groups at any of the time points examined. Similarly, there were no differences among any of the groups for circulating concentrations of TNF-alpha. In rats challenged with endotoxin, dantrolene affected neither survival nor circulating concentrations of TNF-alpha. We conclude that dantrolene decreases survival in bacterial sepsis and has no effect on survival in endotoxemia in rats. The importance of excessive intracellular calcium release in sepsis remains to be elucidated.

Polysaccharide-mediated protection against abscess formation in experimental intra-abdominal sepsis.

Abscess formation is a major complication of intra-abdominal sepsis that causes significant morbidity and mortality. In such cases, Bacteroides fragilis is the predominant anaerobic isolate. In a rat model of intra-abdominal sepsis, the capsular polysaccharide complex (CPC) from B. fragilis promotes abscess formation and when administered sub-cutaneously, protects against this host response by a T cell-dependent immune mechanism. In the present study, the polysaccharide A (PS A) component of CPC protected animals against challenge with live heterologous bacterial species (mixtures of anaerobes and facultative organisms) that are most commonly isolated from intra-abdominal abscesses in humans. Protection against heterologous bacterial challenge was transferred by T cells. Administration of PS A shortly before or even after challenge with B. fragilis protected against this host response. In experiments designed to simulate fecal contamination of the human peritoneal cavity, PS A protected animals against abscess formation induced by a rat cecal contents inoculum. The surprisingly broad protective activity of PS A indicates that this molecule is likely suppressing a nonspecific host tissue reaction that forms in response to a variety of abscess-inducing organisms and that it might be useful in preventing abscess formation associated with intra-abdominal sepsis in the clinical setting.

Structure and function of Bacteroides fragilis capsular polysaccharides: relationship to induction and prevention of abscesses.

The capsular polysaccharide complex (CPC) of Bacteroides fragilis exhibits unusual biological properties. This polysaccharide complex promotes the formation of intraabdominal abscesses and, when administered systemically, can prevent abscess induction in a rat model of intraabdominal sepsis. Each of these biological properties is mediated by a T cell-dependent immune mechanism. The CPC consists of two distinct polysaccharides, PS A and PS B, each with repeating units that have positively charged amino groups and negatively charge carboxyl or phosphate groups. Analysis of these polysaccharides as well as of other charged polysaccharides of bacterial origin, before and after chemical modification, revealed that the oppositely charged groups are required for promotion of intraabdominal abscesses as well as for the distinct properties associated with the B. fragilis CPC and delineate one mechanism by which these biological responses occur.

Induction of the heat shock response reduces mortality rate and organ damage in a sepsis-induced acute lung injury model

To test the hypothesis that induction of heat shock proteins before the onset of sepsis could prevent or reduce organ injury and death in a rat model of intra-abdominal sepsis and sepsis-induced acute lung injury produced by cecal ligation and perforation. Prospective, blind, randomized, controlled trial. University research laboratory. One-hundred forty-two adult Sprague-Dawley rats (weight range 200 to 300 g). Production of intra-abdominal sepsis and exposure to heat stress. Animals were randomly divided into four groups: heated and septic, heated and sham-septic, unheated and septic, and unheated and sham-septic. We evaluated the mortality rate and pathologic changes in lung, heart, and liver at 18 hrs after cecal perforation, at 24 hrs after removal of the cecum, and at 7 days after perforation. Heated animals exhibited a maximum increase in heat shock protein of 72 kilodalton molecular weight protein concentrations in the lungs and heart 6 to 24 hrs after the hyperthermic stress. By 18 hrs after perforation, 25% of the septic, unheated animals had died whereas none of the septic heated animals had died (p < .005). Septic, heated animals showed a marked decrease in 7-day mortality rate (21%) compared with septic unheated animals (69%) (p < .01). Furthermore, septic heated animals showed less histologic evidence of lung and liver damage than septic unheated animals. These data suggest that thermal pretreatment, associated with the synthesis of heat shock proteins, reduces organ damage and enhances animal survival in experimental sepsis-induced acute lung injury. Although the mechanisms by which heat shock proteins exert a protective effect are not well understood, these data raise interesting questions regarding the importance of fever in the protection of the whole organism during bacterial infection.

Suppression of delayed cutaneous hypersensitivity and inflammatory cell delivery by sterile barium peritonitis

We have previously shown that experimental peritonitis secondary to fecal bacteria plus barium sulfate suppresses delayed cutaneous hypersensitivity (DCH) in rats. We examined herein the role of barium sulfate. In a series of experiments presensitized rats were simultaneously skin tested with intradermal keyhole limpet hemocyanin and given an intraperitoneal injection of either (1) a mixture of four fecal bacteria in their nutrient broths, (2) bacteria and broths plus barium sulfate, (3) sterile broths plus barium, (4) sterile barium alone, (5) nutrient broths, or (6) saline. In rats given sterile barium we measured phagocyte delivery to subcutaneous polyvinyl alcohol sponges. We found that (1) the coadministration of barium sulfate was necessary for rats given bacteria to die ( P = 0.03) or develop abdominal abscesses ( P < 0.005), (2) suppression of DCH occurred in 70% of rats receiving sterile barium sulfate vs 0% in saline controls ( P = 0.0001), (3) early suppression of DCH was associated with subsequent death and abscess formation in rats given bacteria plus barium ( P = 0.00002) and with intraabdominal barium collections in rats given barium alone ( P < 0.02), (4) barium sulfate administration caused suppression of phagocyte delivery to subcutaneous sponges: 23.2 × 10 6 cells/site vs 43.1 × 10 6 cells/site in saline controls ( P < 0.005). We conclude that barium sulfate itself has profound systemic effects in the rat model of intraabdominal sepsis. Early suppression of DCH is associated with a poor outcome in septic rats.

Protective Efficacy of Immunization with Capsular Antigen against Experimental Infection with Bacteroides fragilis

The protective efficacy afforded by immunization with the capsular antigen of Bacteroides fragilis against abscess formation and bacteremia due to this organism was studied in an experimental rat model of intraabdominal sepsis. Of unimmunized animals, animals immunized with methylated bovine serum albumin and complete Freund's adjuvant, and animals immunized with lipopolysaccharide of Bacteroides thetaiotaomicron, greater than 90% developed abscesses when challenged intraperitoneally with strains of B. fragilis or Bacteroides distasonis (given with an enterococcus) or with the cecal contents of meat-fed rats. In contrast, animals immunized with B. fragilis capsular polysaccharide, given with or without methylated bovine serum albumin and complete Freund's adjuvant, and animals immunized with the outer membrane of B. fragilis strain 23745 were protected to a significant degree from abscesses caused by challenge with B. fragilis or B. distasonis. Such immunization had no overall effect on the development of abscesses in animals challenged with the entire cecal contents of meat-fed rats; however, B. fragilis was eliminated from the abscesses of these animals. Animals immunized with the capsular polysaccharide were protected from early B. fragilis bacteremia.