Bacterial Translocation of Intestinal Pseudomonas aeruginosa in Post-Burn Infection of Mice

Remote Intestinal Injury Early After Experimental Polytrauma and Hemorrhagic Shock

Dysfunction of the gut-blood barrier plays an important role in many diseases, such as inflammatory bowel disease, hemorrhagic shock (HS), or burn injury. However, little is known about gut barrier dysfunction after hemodynamically instable polytrauma (PT). Therefore, we aimed to evaluate the effects of PT and HS on remote intestinal damage and barrier dysfunction, especially regarding the role of zonula occludens protein 1 (ZO-1) as an important tight junction protein.Male C57BL/6 mice were subjected to either PT (thorax trauma, closed head injury, soft tissue injury, and distal femoral fracture), 60 min of pressure-controlled HS (30 ± 5 mmHg), or PT+HS, or sham procedures.Animals of all trauma groups showed an increase in abdominal girth and dilation of the intestine during the experimental period, which was largest in the PT+HS group. Increased blood-tissue permeability to albumin (assessed by Evans blue dye) was found in the HS group. Experimental groups showed a slight increase in plasma concentration of intestinal fatty acid binding protein and some intestinal damage was histologically detectable. Of note, PT+HS animals revealed significantly reduced expression of ZO-1 in intestinal epithelial cells. In an in-vitro model, stimulation of human colon epithelial cells with peptidoglycan, but not with lipopolysaccharide, resulted in elevated secretion of pro-inflammatory cytokines, reflecting inflammatory activity of the intestinal epithelium.Taken together, PT and HS lead to increased permeability of the gut-blood barrier. Bacterial components may lead to production of inflammatory and chemotactic mediators by gut epithelial cells, underlining the role of the gut as an immunologically active organ.

Role of Motility in the Endogenous Pseudomonas aeruginosa Sepsis after burn

We investigated the relationship between bacterial motility and the lethal endogenous sepsis after burn in mice orally challenged with Pseudomonas aeruginosa, by using motility mutants. The mortality rates of postburn endogenous sepsis in mice orally challenged with low-motility mutants (strains B16-40 and B16-46) were 12% and 7.7%, respectively. By contrast, the mortality rates in mice who had been fed a high-motility mutant (B16-52) or the parental P. aeruginosa B16 (a high-motility strain) were 36% and 33%, respectively. Significant differences were found for mortality rates in groups fed the high-motility or lowmotility strains. A multiple regression analysis examining the effect of motility, number of cecal P. aeruginosa cells, and production of exotoxin A and total protease on the murine mortality rates associated with the 3 motility mutants and the parental strain showed a linear relationship between murine mortality and bacterial motility. In addition, when human monoclonal antibody specific for type-b flagella proteins of P. aeruginosa was intravenously administrated to mice orally challenged with P. aeruginosa B16, the mortality rate significantly decreased to 5.6%, compared with 33% in similar mice given intravenous saline. These results suggest that the occurrence of the lethal endogenous sepsis after burn in mice was closely related to the motility of the P. aeruginosa colonized in their intestinal tract, and that motility is an important virulence factor in endogenous P. aeruginosa sepsis after burn injury.

A mouse model for postoperative fatal enteritis due to Staphylococcus infection

BACKGROUND

Postoperative infection of intestine with methicillin-resistant Staphylococcus aureus (MRSA) is fatal in some cases. The object of this study was to establish a mouse model for the infection, providing a useful tool for investigating mechanisms in the progression of infection.

METHODS

Mice were pretreated with cyclophosphamide, injected orally or directly into jejunum with MRSA prepared from a postoperative patient, and then given 5 daily doses of antibiotics. Forty-eight hours after the injection, bacterial translocation and serum endotoxin levels were examined. Macrophage depletion was carried out by the administration of liposome-encapsulated dichloromethylene diphosphate (Cl(2)MDP), 4 days before MRSA injection.

RESULTS

Injection into the jejunum but not oral administration of MRSA induced enteritis with diarrhea and resulted in death in most cyclophosphamide-treated mice. Translocation of MRSA in mesenteric lymph nodes and liver was observed, concomitantly with E. coli infection. Endotoxin-resistant C3H/HeJ mice infected with MRSA survived longer than endotoxin-sensitive C3H/He mice, but also died within a week after MRSA injection. Selective depletion of macrophages induced infection in mice that were not pretreated with cyclophosphamide.

CONCLUSION

We established a mouse model for the fatal MRSA infection which induced enteritis with diarrhea, that will be a useful tool for investigating the mechanisms for sometimes fatal MRSA infection of the intestine in postoperative patients. The presence of E. coli or endotoxin seemed to play a major role in the mortality of mice in the early days of MRSA-induced enteritis, but other factors, probably from MRSA, in the later days. Phagocytes were quite important for protection against the MRSA infection.