Enhancement of survival from murine polymicrobial peritonitis with increased abdominal abscess formation

Meta-analysis of the effect of peritoneal lavage on survival in experimental peritonitis

Background

Morbidity and mortality associated with bacterial peritonitis remain a challenge for contemporary surgery. Despite great surgical improvements, death rates have not improved. A secondary debate concerns the volume and nature of peritoneal lavage or washout—what volume, what carrier and what, if any, antibiotic or antiseptic?

Methods

A literature search of experimental studies assessing the effect of peritoneal lavage following peritonitis was conducted using Medline, EMBASE and Cochrane databases. Twenty-three trials met predetermined inclusion criteria. Data were pooled and relative risks calculated.

Results

In an experimental peritonitis setting a mortality rate of 48·9 per cent (238 of 487) was found for saline lavage compared with 16·4 per cent (106 of 647) for antibiotic lavage (absolute risk reduction (ARR) 32·5 (95 per cent confidence interval (c.i.) 27·1 to 37·7) per cent; (P < 0·001). An ARR of 25·0 (95 per cent c.i. 17·9 to 31·7) per cent P < 0·001) was found for the use of saline compared with no lavage at all. The survival benefit persisted regardless of systemic antibiotic therapy. Antiseptic lavage was associated with a very high mortality rate (75·0 per cent).

Conclusion

Pooled data from studies in experimental peritonitis demonstrated a significant reduction in mortality with antibiotic lavage.

Endotoxin and muramyl dipeptide modulate surface receptor expression on human mononuclear cells

Endotoxin (lipopolysaccharide (LPS), 100 ng/ml) and muramyl dipeptide (MDP 100 ng/ml), two immunomodulatory bacterial cell wall products, were incubated with human whole blood, and the expression of receptors involved in antigen presentation, costimulation, and cell activation was investigated by use of flow cytometry. On monocytes, LPS and MDP increased surface expression of human leukocyte antigen-DR (HLA-DR), CD18, CD54 (intercellular adhesion molecule-1, ICAM-1), and CD86 (B7-2). On lymphocytes, LPS but not MDP increased HLA-DR expression after 18 h. The expression of CD28, CD49d/CD29, and CD106 (vascular cell adhesion molecule-1, VCAM-1) remained unchanged on both monocytes and lymphocytes. The early increase (1-6 h) of CD18 and ICAM-1 expression led us to hypothesize that CD18-dependent costimulatory signals were involved in the later (6 h) increase of monocyte HLA-DR expression. However, blocking studies using monoclonal antibodies against CD18 (IB4, 15 microg/ml) demonstrated that the LPS- and MDP-induced increase of HLA-DR and ICAM-1 expression on monocytes was not mediated through CD18. LPS induced the expression of the early activation marker CD69 by a CD14-dependent but CD18-independent mechanism, whereas MDP did not induce CD69 expression. Analysis of leukocyte subsets demonstrated that CD4(+) T-cells, CD8(+) T-cell, CD19(+) B-cells, CD56(+) natural killer (NK)-cells, and CD14(+) monocytes increased the expression of CD69 after stimulation with LPS. Collectively, these data demonstrate a stronger immunomodulatory effect of LPS compared with MDP which may, in part, explain the established difference of toxicity between these two bacterial cell wall products.

Age-dependent susceptibility to intraabdominal abscess formation

Infection remains a major cause of morbidity and mortality in the surgical neonate, with the risk of developing infectious complications decreasing as age increases. Developmental changes in the immune system, as well as transplacentally acquired immunity, likely play a role in this differential risk. The purpose of this study was to determine whether there is an age-related susceptibility to intraabdominal abscess formation. The authors used a mouse model in which the combination of an aerobe, anaerobe, and adjuvant routinely forms abscesses. Litters of at least six C57 BL/6 mice were used. The mice received 10(7) of Enterococcus faecalis and 10(7) Bacteroides distasonis or 10(7) B distasonis alone. The mice were given 8 microL/g of 50% wheat bran (40 mg/mL) and 50% bacteria. There were at least four litters for each experiment. Intraabdominal abscesses were counted after 7 days. Ten-day-old mice had an incidence of intraabdominal abscesses that was similar to that of the adults (81% v 91%). There was a significant decrease in intraperitoneal infection after 10 days, until weaning (37% and 38%; P < .05). The authors conclude that there are significant developmental changes in susceptibility to intraabdominal abscess formation, which may reflect changes in peritoneal defense mechanisms.

Molecular adjuvants and immunomodulators: new approaches to immunization

Epitopes on microbial antigens responsible for protective immunity have begun to be identified and isolated, and their chemical structures have been determined. Ensuing knowledge of their weak immunizing capacity per se has led to an appreciation of the need for adjuvants to increase the immunogenicity of these low-molecular-weight synthetic structures. As such, a recent surge in adjuvant research has emerged. Accordingly, this review will highlight a number of those adjuvant substances whose activity in animals indicates a potential use in human vaccines. In addition, the potential of several well-defined substances, termed immunomodulators, which nonspecifically stimulate resistance of animals to multiple 50% lethal doses of microbial challenge is described. Among the most extensively characterized adjuvants of microbial origin discussed in detail are (i) the lipopolysaccharides isolated from gram-negative bacteria and their nontoxic analogs, (ii) the synthetic muramyl dipeptides and their multiple analogs, and (iii) the synthetic polyribonucleotide complexes, mimicking the interferon-inducing capacity of viruses. Discussed also are the heat-labile enterotoxin of Escherichia coli, the nonionic block copolymers, the saponins, a quinolamine derivative, and the hormone dihydroepiandrosterone.

Effect of Escherichia coli lipopolysaccharide on Bacteroides fragilis abscess formation and mortality in mice

To study the mechanism of synergism between Bacteroides fragilis and Escherichia coli, the effect of sublethal dose of E. coli lipopolysaccharide (LPS) (25 micrograms/mouse) was checked on B. fragilis abscess formation. LPS was administered prior or after inoculum injection. No significant difference in the abscess size was observed at necropsy on day 6. However, all the groups receiving LPS showed higher incidence of recovery of additional intestinal bacteria (23.5-45.5%) from the abscess pus. When LPS was given 4 hr prior to inoculum administration, 83-100% mortality was observed. Detailed investigation showed autoclaved cecal contents alone could also cause similar mortality. Studies with stimulation of endogenous cytokines by E. coli LPS demonstrated induction of all of them within 3 hr in the blood stream with TNF-alpha demonstrating peak at 1 hr, IL-1 alpha and IL-6 at 4 hr and IFN-gamma between 6-9 hr with moderately high levels at 4 hr. This E. coli LPS-triggered cytokine cascade possibly gets further stimulated by injection of autoclaved cecal contents containing high concentration of endotoxins (1.6 x 10(5) EU/ml) contributed by dead bacteria and lead to the mortality of animals.

Regional cellular responses to intraperitoneal infection

Leucocytes in different body compartments were examined in a murine intra-abdominal abscess model: (i) peripheral blood; (ii) peritoneal exudate; (iii) abscess wall; and (iv) abscess pus, with respect to their phagocytic ability, CR3 expression and Ia antigen expression (murine MHC antigen). The ability of serum or supernatant in each compartment to opsonize Staphylococcus aureus was also determined. Mice responded to caecal ligation and puncture (CLP) with systemic monocytosis, an increased amount of opsonins in peritoneal fluid and an increased phagocytosis in pus leucocytes. This increased phagocytic ability and CR3 expression both subsequently decreased. Monocyte/macrophage Ia expression was reduced in all measured compartments over time. In contrast, sham-operated animals, without an intra-abdominal abscess, responded to operation with an even greater increase in peritoneal exudate phagocytic ability and in monocyte/macrophage Ia expression in all compartments which was sustained beyond 1 week. Decreased peritoneal exudate cell and peripheral blood Ia was still present after 28 days in CLP animals, compared with both sham and normal animals (P less than 0.05, P less than 0.02, respectively). For all parameters, changes observed in peripheral blood did not reflect those present near the site of infection. Proper understanding of local or regional infection must take into account and ultimately alter these generally unappreciated changes in and about the actual site of infection.

Intra-abdominal sepsis: the role of surgery

The role of the surgeon in intra-abdominal sepsis is multifactorial. A comprehensive understanding of the incidence and pathophysiology of diseases which cause intra-abdominal sepsis is the key to the diagnosis and treatment of such ailments. In simplest terms, the aetiology has two basic mechanisms: (a) violation of the 'bug-body barrier' and (b) obstruction to the flow of a body fluid with subsequent bacterial overgrowth. Either of these mechanisms may affect any of the organs within the abdomen, leading to sepsis. The peritoneal cavity is a dynamic structure which responds to insults in certain predictable manners which notify the alert physician that danger is present. Recognition of these signs through history and physical examination are the most important aspects of diagnosis. Confirmation of suspicions can be obtained with radiological modalities, but they are not a substitute for clinical judgement. Treatment of intra-abdominal sepsis should always begin with resuscitation and systemic antibiotics. Alleviation of the septic source is mandatory, and this may be achieved either operatively or non-operatively (i.e. percutaneous or endoscopic procedures). When the patient does not improve after the initial procedure, then a missed focus of infection must be investigated. In some cases, a planned or staged second operation may be needed to further debride necrotic tissue. Antibiotics should be of adequate spectrum and bioavailability to kill the species of bacteria most likely to cause the infection. This regimen may be altered when culture and sensitivity reports are completed. Finally, patients whose immune system function has been altered by disease or treatment must be assumed very ill until proven otherwise. These are general guidelines in the management of patients with intra-abdominal sepsis. Individual cases may necessitate slight modifications, but all require a high level of vigilance and expertise in order to combat a very lethal disease.

Wound tissue respiratory burst and local microbial inflammation

Local and systemic chemiluminescent (CL) response was measured in 32 patients with wound infection and in 27 patients with crush syndrome complicated by severe wound infection. The level of wound CL depends upon the local microbial concentration and the dynamics of wound healing. CL response of neutrophils in circulation was higher in higher local CL response, but extremely high wound microbial concentration (greater than 10(8) CFU/g) suppressed both local and systemic responses. No metabolic reserve was observed in wound tissue. Wound healing was characterized by changes in the mode of local CL response: from a prevalence of luminol-dependent (neutrophilic) CL to a prevalence of lucigenin-independent (macrophagal) CL.