Influence of selective decontamination of the digestive tract on cell-mediated immune function and bacteria/endotoxin translocation in thermally injured rats

Burn-Induced Local and Systemic Immune Response: Systematic Review and Meta-Analysis of Animal Studies

As burn injuries are often followed by a derailed immune response and excessive inflammation, a thorough understanding of the occurring reactions is key to prevent secondary complications. This systematic review, that includes 247 animal studies, shows the post-burn response of 14 different immune cell types involved in immediate and long-term effects, in both wound tissue and circulation. Peripheral blood neutrophil and monocyte numbers increased directly after burns, whereas thrombocyte numbers increased near the end of the first week. Lymphocyte numbers, however, were decreased for at least two weeks. In burn wound tissue, neutrophil and macrophage numbers accumulated during the first three weeks. Burns also altered cellular functions as we found increased migratory potential of leukocytes, impaired antibacterial activity of neutrophils and enhanced inflammatory mediator production by macrophages. Neutrophil surges were positively associated with burn size and were highest in rats. Altogether, this comprehensive overview of the temporal immune cell dynamics shows that unlike normal wound healing, burn injury induces a long-lasting inflammatory response. It provides a fundamental research basis to improve experimental set-ups, burn care and outcome.

Survival benefit of the full selective digestive decontamination regimen

PURPOSE

We assessed the impact of the full protocol of selective decontamination of the digestive tract (SDD) using parenteral and enteral antimicrobials on mortality.

MATERIALS AND METHODS

A systematic review was performed searching MEDLINE, EMBASE, the Cochrane Register of Controlled Trials, previous meta-analyses, and conferences proceedings. We included all randomized controlled trials (RCTs) comparing the full protocol of SDD, including oropharyngeal and intestinal administration of antibiotics combined with the parenteral component, with no treatment or placebo. The primary end points were overall mortality, mortality attributable to infection, early, and late mortality.

RESULTS

Twenty-one RCTs on 4902 patients were included. Overall mortality was significantly reduced (odds ratio [OR], 0.71; 95% confidence interval [CI]; 0.61-0.82; P < .001). There was a nonsignificant reduction in infection-related mortality (6 RCTs; OR, 0.40; 95% CI, 0.10-1.59; P = .19) and early mortality (4 RCTs; OR, 0.64; 95% CI, 0.34-1.19; P = 0.16), and a significant reduction in late mortality (5 RCTs; OR, 0.56; 95% CI, 0.40-0.77; P < .001). The subgroup analysis showed a significant mortality reduction in successfully decontaminated patients (OR, 0.58; 95% CI, 0.45-0.77; P < .001), and when parenteral and enteral antimicrobials were administered to every patient receiving treatment in the intensive care unit (OR, 0.59; 95% CI, 0.42-0.82; P < .001).

CONCLUSIONS

The findings strongly indicated that the full protocol of SDD reduces mortality in critically ill patients, in particular when successful decontamination is obtained. Eighteen patients should be treated with SDD to prevent one death.

Reducing susceptibility to bacteremia after experimental burn injury: a role for selective decontamination of the digestive tract

We proposed that selective decontamination of the digestive tract (SDD) initiated after experimental burn injury would decrease myocardial inflammation and dysfunction after a second insult such as septic challenge. Rats were divided into eight experimental groups. Groups included sham burn plus sham sepsis, burn alone, sepsis alone, and burn plus sepsis given either water by oral gavage for 5 days after burn (or sham burn) or given oral antibiotics (polymyxin E, 15 mg; tobramycin, 6 mg; 5-flucytosin, 100 mg given by oral gavage, 2x daily for 5 days after burn or sham burn). Cardiac function and inflammation were studied 24 h after septic challenge. In the absence of SDD, burn alone, sepsis alone, or burn plus septic challenge promoted cardiac myocyte secretion of TNF-alpha (burn, 174+/-11; sepsis, 269+/-19; burn+sepsis, 453+/-14 pg/ml), IL-1beta (burn, 35+/-2; sepsis, 29+/-1; burn+sepsis, 48+/-7 pg/ml), and IL-6 (burn, 143+/-18; sepsis, 116+/-3; burn+sepsis, 248+/-12 pg/ml) compared with values measured in sham (TNF-alpha, 3+/-1; IL-1beta, 1+/-0.4; IL-6, 6+/-1.5 pg/ml) (P<0.05). Impaired ventricular contraction and relaxation responses were evident in the absence of SDD [burn+sepsis: left ventricular pressure (LVP), 65+/-4 mmHg; rate of LVP rise (+dP/dt), 1,320+/-131 mmHg/s compared with values measured in sham: LVP, 96+/-4 mmHg; +dP/dt, 2,095+/-99 mmHg/s, P<0.05]. SDD treatment of experimental burn attenuated septic challenge-related inflammatory responses and improved myocardial contractile responses, producing cardiac TNF-alpha, IL-1beta, and IL-6 levels, LVP, +dP/dt, and rate of LVP fall (-dP/dt) values that were significantly better (P<0.05) than values measured in burn plus sepsis in the absence of SDD. This work confirms that endogenous gut organisms contribute to sensitivity to subsequent infectious challenge.

The role of bifidobacteria in gut barrier function after thermal injury in rats

BACKGROUND

Early multiple organ dysfunction syndrome appears to be facilitated with bacterial translocation in severe burn injury, yet the mechanisms of bacterial translocation remain in dispute. The aim of this study was to characterize the potential role of intestinal bifidobacteria in the pathogenesis of gut-derived bacterial translocation after burns and to analyze the effects of bifidobacterial supplement on gut barrier function.

METHODS

Wistar rats were randomly divided into burn group (Burn, n = 60), sham burn group (SB, n = 10) in experiment 1, and burn + saline group (BS, n = 30), burn + bifidobacteria group (BB, n = 30), and sham-burn + saline group (SS, n = 30) in experiment 2. Animals in BB group were fed bifidobacterial preparation (5 x 10(9) CFU/mL) after burns, 1.5 mL, twice daily. Animals in BS and SS were fed saline. Samples were taken on postburn days 1, 3, and 5. The incidence of bacterial translocation and counts of Bifidobacterium, fungi and Escherichia coli in gut mucosa, as well as the sIgA levels in mucus of the small intestine were determined. The positive sIgA expression in lamina propria and ileum mucosal injury were evaluated light microscopically by blinded examiners.

RESULTS

The incidence of bacterial translocation was increased after burns, which was accompanied by significant decrease in number of bifidobacteria but significant increase in E. coli and fungi in gut mucosa, and elevation of levels of plasma endotoxin and IL-6 (p < 0.001). The incidence of bacterial translocation was markedly reduced after 3- and 5-day supplementation of bifidobacteria compared with control group (p < 0.05). The counts of mucosal bifidobacteria were increased by 4- to 40-fold, whereas E. coli and fungi were decreased by 2- to 30-fold and 10- to 150-fold, respectively, after bifidobacterial supplementation. The damage of mucosa tended to be less pronounced after 3-day bifidobacteria-supplemented formula compared with control group (grade 2 [0-6] versus grade 4 [3-6], p < 0.05). Moreover, the expression and release of sIgA was markedly augmented after 3-days of bifidobacteria-supplementation formula and it returned to normal range on postburn day 5.

CONCLUSIONS

The decrease in counts and proportion of bifidobacteria to other flora in gut may play an important role in the development of bacterial translocation after thermal injury. Supplementation of exogenous bifidobacteria could improve gut barrier function, and attenuate bacterial/endotoxin translocation secondary to major burns.

Role of the gastrointestinal tract in burn sepsis

During the last 50 years, our understanding of the role of the gastrointestinal tract as a first-line defense against the development of postburn sepsis has increased dramatically. Starting with the concept of that gut-derived bacteria cause distant injury, investigators have delineated a complex series of physical changes in the barrier of the gastrointestinal tract. Along with an understanding of these physical changes has come an appreciation of the role of the immune system in modulating postburn organ failure. Importantly, recent investigations into the role of mesenteric lymph have fundamentally changed the paradigm of organ failure and have implicated the gut as a cytokine-secreting organ. This article traces the development of key concepts in the study of burn sepsis and their clinical implications.

Selective decontamination of the digestive tract attenuated the myocardial inflammation and dysfunction that occur with burn injury

This study examined the effects of oral antibiotics to selectively decontaminate the digestive tract (SDD) on postburn myocardial signaling, inflammation, and function. We hypothesized that antibiotic therapy to eliminate pathogens from the gastrointestinal (GI) tract would reduce myocardial inflammatory responses and improve postburn myocardial performance. Sprague-Dawley rats received polymyxin E (15 mg), tobramycin (6 mg), and 5-flucytosin (100 mg) by oral gavage twice daily for 3 days preburn and 24 h postburn. Experimental groups included 1) sham burn given vehicle (3 ml water), 2) sham plus SDD, 3) burn over 40% total body surface area (TBSA) plus SDD, and 4) burn over 40% TBSA given vehicle. All burns received lactated Ringer solution (4 mg·kg−1·%burn−1); myocardial signaling (PKCε/p38 MAPK/NF-κB) was studied 2, 4, and 24 h postburn; and cytokine secretion (systemic and myocyte secreted cytokines, ELISA) and cardiac function were examined 24 h postburn. Vehicle-treated burn injury increased myocardial PKCε/p38 MAPK expression, promoted NF-κB nuclear translocation, promoted TNF-α, IL-1β, IL-6, and IL-10 secretion, and impaired myocardial function. SDD attenuated burn-related proinflammatory myocardial signaling, cytokine secretion, and myocardial contractile defects. Our data suggest that burn-related loss of GI barrier function and translocation of microbial products serve as upstream mediators of postburn myocardial inflammatory signaling and dysfunction.

Risk factors of development of gut-derived bacterial translocation in thermally injured rats

AIM: Studies have demonstrated that gut-derived bacterial translocation (BT) might play a role in the occurrence of sepsis and multiple organ dysfunction syndrome (MODS). Yet, no convincing overall analysis of risk factors for BT has been reported. The purpose of this study was to evaluate the related factors for the development of BT in burned rats.

METHODS: Wistar rats were subjected to 30% third-degree burns. Then samples were taken on postburn d 1, 3, and 5. Incidence of BT and counts of mucosal bifidobacteria, fungi and E. coli, mucus sIgA, degree of injury to ileal mucosa, and plasma interleukin-6 were observed. Univariate analysis and multivariate logistic regression analysis were performed.

RESULTS: The overall BT rate was 53.9% (69 in 128). The result of univariate analysis showed that the levels of plasma endotoxin and interleukin-6, the counts of mucosal fungi and E. coli, and the scores of ileum lesion were markedly increased in animals with BT compared with those without (P = 0.000-0.005), while the levels of mucus sIgA and the counts of mucosal bifidobacteria were significantly reduced in animals with translocation compared with those without (P = 0.000). There was a significant positive correlation between mucus sIgA and the counts of mucosal bifidobacteria (r = 0.74, P = 0.001). Moreover, there were strong negative correlations between scores of ileum-lesion and counts of bifidobacteria (r = -0.67, P = 0.001). Multivariate logistic regression revealed that ileum lesion score (odds ratio [OR] 45.52, 95% confidence interval [CI] 5.25-394.80), and counts of mucosal bifidobacteria (OR 0.039, 95% CI 0.0032-0.48) were independent predictors of BT secondary to severe burns.

CONCLUSION: Ileal lesion score and counts of mucosal bifidobacteria can be chosen as independent prognosis factors of the development of BT. Specific interventions targeting these high-risk factors might be implemented to attenuate BT, including strategies for repair of damaged intestinal mucosae and restoration of the balance of gastrointestinal flora.

Dissemination of bacteria in multiple organs associated with apoptosis and macrophage activity in different stages of experimental sepsis

BACKGROUND

Gram negative sepsis is reported to induce massive translocation of bacteria into tissues, which associates with decreased macrophage function and increased macrophage apoptosis.

AIMS

The objective of this study was to detect the translocation of bacteria into different organs and to evaluate macrophage activity and the apoptosis of macrophages in the liver during different stages of sepsis and to correlate these parameters.

MATERIAL

Wistar rats (n = 43) were inoculated intraperitoneally with an E. coli and divided into 5 groups, which were killed at different times.

METHODS

Counts of translocated bacteria in tissues were evaluated by using morphological and bacteriological methods. Macrophage activity and apoptotic cells in the liver were studied by applying immunohistochemical methods.

RESULTS

The counts of E. coli were the highest in the organs and blood 6 h after the onset of sepsis, being in correlation with the highest counts of apoptotic cells in the liver and the falling counts of activated macrophages. The counts of microbes show a new wave of elevation in tissues by 120th h.

CONCLUSIONS

The massive penetration of bacteria, the depressed macrophage response in early sepsis following the increased rate of apoptotic macrophages, the different rate of bacterial multiplication in tissues and blood and the second wave of the multiplication of bacteria in tissues in late sepsis all refer to the significance of developing immune dysfunction.

All great truths are iconoclastic: selective decontamination of the digestive tract moves from heresy to level 1 truth

OBJECTIVE

The objective was to compare evidence of the effectiveness, costs and safety of the traditional parenteral antibiotic-only approach against that gathered from 53 randomised trials involving more than 8,500 patients and six meta-analyses on selective decontamination of the digestive tract (SDD) to control infection on the intensive care unit (ICU). PHILOSOPHY: Traditionalists believe that all infections are due to breaches of hygiene except those established in the first 2 days, and that all micro-organisms can cause death. In contrast, newer insights show that transmission via the hands of carers are responsible only for infections occurring after one week, and that only a limited range of 15 potential pathogens contribute to mortality. INTERVENTIONS TO PREVENT ICU INFECTION: The traditional approach is based on hand disinfection aiming at the prevention of transmission of all micro-organisms, to control all infections that occur after 2 days on the ICU. The second feature is the restrictive use of systemic antibiotics, only in cases of microbiologically proven infection. In contrast, SDD aims to control the three types of infection: primary, secondary endogenous and exogenous due to 15 potential pathogens. The classical SDD tetralogy comprises four components: (i) a parenteral antibiotic, cefotaxime, administered for three days to prevent primary endogenous infections typically occurring "early"; (ii) the oropharyngeal and enteral antimicrobials, polymyxin E, tobramycin and amphotericin B administered in throat and gut throughout the treatment on the ICU to prevent secondary endogenous infections tending to develop "late"; (iii) a high standard of hygiene to control transmission of potential pathogens; and (iv) surveillance samples of throat and rectum to monitor the efficacy of the treatment.

ENDPOINTS

(i) Infectious morbidity; (ii) mortality; (iii) antimicrobial resistance; and (iv) costs.

RESULTS

Properly designed trials on hand disinfection have never demonstrated a reduction in either pneumonia and septicaemia, or mortality. Two randomised trials using restrictive antibiotic policies failed to show a survival benefit at 28 days. In both trials the proportion of resistant isolates obtained from the lower ways was >60% despite significantly less use of antibiotics in the test group. A formal cost effectiveness analysis of the traditional antibiotic policies has not been performed. On the other hand, two meta-analyses have shown that SDD reduces the odds ratio for lower airway infections to 0.35 (0.29-0.41) and mortality to 0.80 (0.69-0.93), with a 6% overall mortality reduction from 30% to 24%. No increase in the rate of super infections due to resistant bacteria could be demonstrated over a period of 20 years of clinical research. Four randomised trials found the cost per survivor to be substantially lower in patients receiving SDD than for those traditionally managed.

CONCLUSIONS

The traditionalists still rely on level 5 evidence, i.e. expert opinion, with a grade E recommendation, whilst the proponents of SDD are able to cite level 1 evidence allowing a grade A recommendation in their attempts to control infection on the ICU. The main reason for SDD not being widely used is the primacy of opinion over evidence.

Gut overgrowth with abnormal flora: the missing link in parenteral nutrition-related sepsis in surgical neonates

BACKGROUND AND AIMS

Patients receiving parenteral nutrition are at risk of septicaemia. Intestinal dysmotility and impaired gut immunity due to parenteral nutrition promote bacterial overgrowth. Gut overgrowth with aerobic Gram-negative bacilli (AGNB) impairs systemic immunity. The aim of this study was to determine the potential role of gut overgrowth with AGNB in the pathogenesis of septicaemia related to parenteral nutrition.

METHODS

A prospective 5 y study of surgical infants less than 6 months of age was undertaken. Surveillance samples of the oropharynx and gut were obtained at the start of parenteral nutrition and thereafter twice weekly, to detect AGNB carriage. Blood cultures were taken on clinical indication only.

RESULTS

Two-hundred and eight infants received parenteral nutrition for 6271 days (median 13 days, range 1-512 days). The incidence of AGNB carriage was 42%, whilst the septicaemia rate was 15%. Eighty-four percent of septicaemic infants carried AGNB, whilst 16% never carried AGNB (P<0.005). Carriage developed significantly earlier than septicaemia.

CONCLUSIONS

The incidence of septicaemia was significantly greater in the subset of abnormal carriers. Although gut overgrowth with abnormal flora reflects illness severity, the fact that it preceded septicaemia implicates AGNB overgrowth, per se, as a contributory factor in the development of septicaemia related to parenteral nutrition. Prevention is unlikely to be successful if it ignores the abnormal flora.

TLR4 inactivation and rBPI(21) block burn-induced myocardial contractile dysfunction

Both large burns and severe gram-negative sepsis are associated with acute myocardial contractile dysfunction. Because others have reported that burn injury may be followed by transient endotoxemia, we hypothesized that bacterial endotoxin induces contractile impairment after burn trauma. We tested this hypothesis in two rodent models. In each model, postburn myocardial contractility was assessed using Langendorff preparations of excised hearts. In the first model, mice expressing either a mutant form of or no Toll-like receptor 4 (TLR4), a critical element of the mammalian endotoxin receptor, were resistant to postburn myocardial contractile dysfunction. In the second model, starting 30 min or 4 h after burn injury, rats were infused with recombinant bactericidal/permeability-increasing protein (rBPI(21)), a protein that binds and neutralizes endotoxin. Hearts from rBPI(21)-treated animals were completely protected from postburn contractile impairment. Because burn-induced contractile dysfunction can be prevented either by blocking signaling through the endotoxin receptor or by neutralizing circulating LPS, bacterial endotoxin may contribute to impaired myocardial contractility after burn injury.

Selective decontamination of the digestive tract in severely burned pediatric patients

Infection is still one of the leading causes of morbidity and mortality in severely burned patients. Evidence suggests that many of the responsible organisms are endogenous. Systemic antibiotic prophylaxis is not effective, and produces resistant strains of microorganisms. SDD has been postulated to be beneficial for controlling and decreasing infections in critically ill patients. Its efficacy in severely burned patients, however, remains controversial. In order to analyze the efficacy of selective decontamination of the digestive (SDD) tract, to decrease the bacterial colonization of the aerodigestive tract and burn wounds, and the incidence of septic complications in severely burned children, 23 pediatric patients affected of severe burns were prospectively randomized in a double-blinded study. Eleven patients received SDD (Polymyxin E, Tobramycin, and Amphotericin B), and 12 placebo. Demographics, hospital course, microbiology results, complications, infectious episodes, and serum levels of IL-1beta, IL-6, IL-10, and TNF-alpha were compared to determine the efficacy of SDD. Colonization rates to the wound, sputum, nasogastric aspirates, and feces were similar. Pneumonia, sepsis and other complications had similar incidence in both groups. Serum levels of all cytokines studied were also comparable, suggesting a similar inflammatory status in all patients, regardless of the treatment received. Patients in the SDD group, however, had a significantly higher incidence of diarrhea (P=0.003). We can conclude that selective decontamination of the digestive tract with Polymixin E, Tobramycin and Amphotericin B is not effective to decrease bacterial colonization and infectious episodes in severely burned pediatric patients.

Selective decontamination of the digestive tract: a life saver

Selective decontamination of the digestive tract (SDD), a strategy designed to prevent or minimize the impact of infection by potentially pathogenic micro-organisms in critically ill patients requiring long-term mechanical ventilation, comprises four component protocols, aiming to control the three types of infection occurring in such cases: (i) a parenteral antibiotic, cefotaxime, administered for a few days to prevent primary endogenous infections typically occurring 'early'; (ii) the topical antimicrobials polymyxin E, tobramycin and amphotericin B employed throughout the stay in the intensive care unit to prevent secondary endogenous infections tending to develop 'late'; (iii) a high standard of hygiene to prevent exogenous infections that may occur throughout the stay in the intensive care unit; (iv) surveillance samples of throat and rectum to distinguish between these three types of infection, to monitor the compliance and the efficacy of the treatment, and to detect the emergence of resistance at an early stage. A recent, rigorous, meta-analysis examining 33 randomized SDD trials involving 5727 patients demonstrated a significant reduction in overall mortality (20%) and in the incidence of respiratory tract infections (65%); conclusive evidence that SDD saves the lives of critically ill patients and confirmation that SDD is now an evidence based medicine manoeuvre. This same meta-analysis found no instance of the emergence of resistance or of associated superinfections and/or outbreaks in any of the 33 studies during a period extending upwards of 10 years. By the criterion of cost-per-survivor, four recent randomized trials showed that patient survival is improved more cheaply by employing SDD than by the traditional approaches.

Experimental study of the effects of splenectomy and partial splenectomy on bacterial translocation

BACKGROUND

The aim of this study is to evaluate the effect of splenectomy and partial splenectomy in a burn-induced bacterial translocation model and to study Kupffer cell (KC) morphology and number.

METHODS

Mice were divided into sham-burn and burn groups. Each group was also subdivided to sham-splenectomy, partial-splenectomy, and splenectomy subgroups. At day 0, operations were performed. At the postoperative 10th day, a sham burn or burn injury was made in all animals. Twenty-four hours later, cultures for bacterial translocation were obtained and livers were evaluated for the quantity and morphology of KCs.

RESULTS

Burned-splenectomized animals had significantly decreased bacterial translocation when compared with sham-splenectomized animals (p = 0.031). Interestingly, in both the sham-burned and burned groups, splenectomy subgroups had significantly higher numbers of KCs compared with partial-splenectomy and sham-splenectomy subgroups (p<0.00000). Burn injury caused a significant decrease of KC numbers in all subgroups compared with their correspondent sham-burned subgroups (p<0.05).

CONCLUSION

Results revealed that splenectomy decreases bacterial translocation and also increases the number of KCs.

Effectiveness of antibiotic prophylaxis in critically ill adult patients: systematic review of randomised controlled trials

OBJECTIVE

To determine whether antibiotic prophylaxis reduces respiratory tract infections and overall mortality in unselected critically ill adult patients.

DESIGN

Meta-analysis of randomised controlled trials from 1984 and 1996 that compared different forms of antibiotic prophylaxis used to reduce respiratory tract infections and mortality with aggregate data and, in a subset of trials, data from individual patients.

SUBJECTS

Unselected critically ill adult patients; 5727 patients for aggregate data meta-analysis, 4343 for confirmatory meta-analysis with data from individual patients.

MAIN OUTCOME MEASURES

Respiratory tract infections and total mortality.

RESULTS

Two categories of eligible trials were defined: topical plus systemic antibiotics versus no treatment and topical preparation with or without a systemic antibiotic versus a systemic agent or placebo. Estimates from aggregate data meta-analysis of 16 trials (3361 patients) that tested combined treatment indicated a strong significant reduction in infection (odds ratio 0.35; 95% confidence interval 0.29 to 0.41) and total mortality (0.80; 0.69 to 0.93). With this treatment five and 23 patients would need to be treated to prevent one infection and one death, respectively. Similar analysis of 17 trials (2366 patients) that tested only topical antibiotics indicated a clear reduction in infection (0.56; 0.46 to 0.68) without a significant effect on total mortality (1.01; 0.84 to 1.22). Analysis of data from individual patients yielded similar results. No significant differences in treatment effect by major subgroups of patients emerged from the analyses.

CONCLUSIONS

This meta-analysis of 15 years of clinical research suggests that antibiotic prophylaxis with a combination of topical and systemic drugs can reduce respiratory tract infections and overall mortality in critically ill patients. This effect is significant and worth while, and it should be considered when practice guidelines are defined.