Adherent bacteria: breaching the mucosal barrier?

Bacterial translocation in an experimental intestinal obstruction model. C-reactive protein reliability?

BACKGROUND

Bacterial translocation occurs in preseptic conditions such as intestinal obstruction through unclear mechanism. The C-reactive protein is an acute phase reactant and a marker of ischemia.

METHODS

45 albino male rats were divided into 3 groups each 15 rats. GI control, GII simple intestinal-obstruction and GIII strangulated obstruction. Outcome measures were: (1) Bacteriologic count and typing for intestinal contents, intestinal wall, liver, mesenteric lymph nodes and blood (cardiac and portal) (2) Histopathologic: mucosal injury score, inflammatory cell infiltrate in the wall, MLN, liver, (3) Biochemical: serum CRP, IL-10, mucosal stress pattern (glutathione peroxidase-malonyldialdhyde tissue levels).

RESULTS

(1) Intestinal obstruction associates with BT precursors (Bact-overgrowth, mucosal-acidosis, immuno-incomptence), (2) Bacterial translocation (frequency and density) was found higher in strangulated I.O, that was mainly enteric (aerobic and anaerobic) and mostly E.coli, (3) The pathogen commonality supports the gut origin hypothesis but the systemic inflammatory response goes with the cytokine generating one. (4) The CRP median values for GI, II, III were 0.5, 6.9, 8.5 mg/L, for BT +ve 8 mg/L and 0.75 mg/L for BT -ve rats.

CONCLUSION

Bacterial translocation occurs bi-directional (systemic-portal) in intestinal obstruction and the resultant inflammatory response pathogenesis is mostly 3 hit model. The CRP is a non selective marker of suspected I.O cases. However, it is a reliable marker of BT, BT density and vascular compromise during I.O.

Bacterial translocation (BT) in cirrhosis

Gut flora and bacterial translocation (BT) play an important role in the pathogenesis of the complications of cirrhosis. Research on the pathogenesis of BT and its clinical significance transcends established boundaries between microbiology, cell biology, intestinal pathophysiology, and immunology. This review delineates multiple mechanisms involved in the process of BT, with an emphasis on alterations in intestinal flora and mucosal barrier function, particularly immunological defense mechanisms. Current knowledge on the innate and adaptive immune response that allows a "friendly" communication between bacteria and host is summarized, and alterations occurring in cirrhosis that may facilitate BT are discussed. In addition, definition of a "pathological" BT is proposed together with an analysis of the anatomical site and route of BT. Finally, therapeutic approaches for the prevention of BT in experimental and human cirrhosis are reviewed. Future research in the field of BT in cirrhosis will allow the development of new therapeutic targets in the prevention of infections and other complications of cirrhosis.

Gastrointestinal disorders of the critically ill. Bacterial translocation in the gut

The human gastrointestinal tract is colonized by a dense population of microorganisms, referred to as the bacterial flora. Although the gut provides a functional barrier between these organisms and the host, bacterial translocation is a common event in the healthy person. However, in critically ill patients, with various underlying diseases, this bacterial translocation may lead to infections and consequently to a further reduction in general health status. The mechanism of bacterial translocation is widely, and somehow controversially investigated in vitro and in animal models. In human studies, several diseases have been associated with bacterial translocation. However, methodological shortcomings, insufficient populations and conflicting results leave many open questions. This is also reflected in the various published therapeutic strategies. To overcome this problem more investigations in humans are needed, especially in techniques for detecting bacterial translocation.

Inflammatory consequences of the translocation of bacteria and endotoxin to mesenteric lymph nodes

BACKGROUND

Translocation of intestinal bacteria to mesenteric lymph nodes (MLNs) has been documented in humans under a variety of circumstances, yet its clinical significance remains to be established. The aim of this study was to correlate detectable translocation to MLNs of bacteria and endotoxin with local and systemic signs of inflammation.

METHODS

From each of 10 patients with carcinoma of the cecal region two MLNs were harvested prior to resection. The presence of bacteria and endotoxin in the lymphatic tissue and blood was determined by culture methods and DNA preparation (PCR) and by a Limulus assay, respectively. Inflammatory mediators were determined in plasma and in MLN homogenates.

RESULTS

Viable bacteria were detected in MLNs of 7 patients and in 9 of 20 lymph nodes. PCR revealed traces of bacteria in 4 patients and in 6 of their MLNs. Combining both modalities, the translocation rate was 80% and 55% for patients and MLNs, respectively. There was no detectable bacteremia. Endotoxin was found in the plasma of 7 patients and in 9 MLNs from 5 patients. There was no correlation between culture findings and endotoxin concentrations. Moreover, bacteriological data did not correspond to local or systemic inflammation. The group of MLN with detectable endotoxin differed significantly from LPS-negative nodes with respect to interleukin-6, interleukin-10, and sCD14. Systemic concentrations of endotoxin and inflammatory parameters did not correspond to levels within MLNs.

CONCLUSION

Translocation to MLNs occurs in patients with cecal carcinoma. This, however, seems not to be of major clinical significance if no additional physiologic insults are encountered. Irrespective of the presence of bacteria, there are variations in inflammatory reactions between lymph nodes from one and the same patient, probably reflecting fluctuating response mechanisms to low-grade translocation.

Derangement of mucosal barrier function by bacteria colonizing the rat colonic mucosa

BACKGROUND

Interaction between gut flora and the intestinal barrier may involve changes in permeability.

METHODS

Rats with a colonic segment excluded from faecal transit were surgically prepared. Matched groups were either kept on luminal antibiotics to prevent colonization of the segment or recolonized with mixed rat flora. Permeability to low-dose trinitrobenzenesulphonic acid (TNBS) or trinitrophenol (TNP), and mucosal injury by the compounds at a high dose were tested in antibiotic and recolonized rats (the compounds differ in water solubility but share a common antigenic domain).

RESULTS

Lumen to blood clearance of the hydrophilic probe (TNBS) was faster in recolonized than in antibiotic rats. The hydrophobic compound TNP was absorbed at faster rates than TNBS, but there was no difference between antibiotic and recolonized rats. Instillation of TNBS at a high dose induced mucosal release of inflammatory mediators and tissue myeloperoxidase accumulation in recolonized rats but not in antibiotic rats. Large necrotic lesions with submucosal involvement after TNBS were only observed in recolonized rats. In contrast, TNP induced mucosal inflammation and large lesions with submucosal necrosis both in recolonized and in antibiotic rats.

CONCLUSION

Colonizing bacteria may increase intestinal permeability to hydrophilic compounds and render the mucosa susceptible to injury.

Sodium deoxycholate facilitates systemic absorption of verotoxin 2e from pig intestine

Injection of verotoxin 2e together with sodium deoxycholate, which increases intestinal permeability to macromolecules, into the intestine of pigs resulted in fluid accumulation, intestinal damage, and signs and lesions of edema disease. Intragastric administration of verotoxin 2e to newborn piglets, who normally absorb protein nonspecifically, resulted in systemic verotoxemia. These results suggest that development of natural edema disease requires a state of increased intestinal permeability.