Experimental studies on the role of the gastrointestinal microflora in postsurgical adhesion formation

Introduction: Adhesions occurring after any kind of surgery is a common phenomenon and cause a great deal of morbidity and mortality, incurring a considerable burden on health care systems. Adhesions are especially prominent after lower abdominal and gynecological procedures (60-90 % of patients after one operation) causing infertility, pain syndromes and bowel obstruction as well as complicating subsequent surgery. Despite many attempts there are still no satisfactory ways or means for prophylaxis or treatment. Part of the difficulties is due to lacking in understanding of the basic pathogenesis behind adhesion formation. Infection is regarded as promoting adhesions. Intra-abdominal antibiotics have been used as an adjunct to fertility surgery. Adhesions are particularly common in the abdominal cavity where the close proximity to the gastrointestinal flora may be of importance.

Rationale and Aims: In order to study the role of the microbial flora in adhesion formation a number of studies were undertaken. I) To study the role of the gastrointestinal flora in germfree and conventional rats. II) To study the role of the flora in the germfree and exgermfree states and to develop an objective scoring scale. III) To study healing of colonic anastomoses and adhesion formation in vitamin A-deficient germfree and conventional rats. IV) To study the influence of the gastrointestinal flora and two of its species on adhesion formation around surgical anastomoses. V) To study whether systemic antibiotics may influence adhesion formation.

Materials and methods: Adhesions were induced in rats by established methods and scored blindly according to special scoring scales, one of which was developed during the work and compared with two counterparts. Germfree and monocontaminated rats were kept in steel isolators, the microbial status being monitored weekly. Vitamin A deficiency was induced with special diet and retinyl esters in liver tissue were analyzed with high-performance liquid chromatography (HPLC). Anastomotic bursting pressures and hydroxyproline content were measured.

Results: Germfree rats formed less adhesions than conventional counterparts (p < 0.01). By turning germfree animals into conventional ones by establishing an ordinary intestinal flora (ex-germfree) the propensity to form adhesions returned (p < 0.005). The new scoring scale was not inferior at detecting differences as compared with two other scales. Vitamin A-deficient rats had lower anastomotic bursting pressures than vitamin A sufficient rats (p < 0.0005), whereas vitamin A-status had no impact on adhesion formation but the intestinal flora-status had (p < 0.0005). Adhesion formation Increases the more the flora status approaches the normal state (p < 0.0001). Amoxicillin / clavulanic acid treated conventional rats had less intestinal bacteria (p < 0.05) and formed less adhesions (p < 0.05).

Conclusions: The bacterial flora of the gastrointestinal canal influence adhesion formation but is not essential for adhesions to develop. Restoration of an ordinary flora restores adhesion forming propensity. The new scoring scale is at least as good as scales compared at detecting differences but has advantage in the form of being objective. Vitamin A is important for healing of colonic anastomoses but did not affect adhesion formation whereas the intestinal flora status did, indicating that the mechanisms might be different. The more normal the flora gets the more normal the adhesive response, indicating that different species of bacteria have different adhesiogenic ability. Antibiotics lowering bacterial numbers of the gastrointestinal flora reduce adhesions, but resistance problems may theoretically induce growth of potent adhesiogens.The present findings might help to explain why measures aimed at reducing fibrin do not work on ischemic bowel and around anastomoses and warrant more research, in which germfree animals could be valuable as a model void of the intestinal flora influence.

List of scientific papers

I. Bothin C, Midtvedt T (1992). The role of the gastrointestinal microflora in postsurgical adhesion formation--a study in germfree rats. Eur Surg Res. 24(5): 309-12.
https://pubmed.ncbi.nlm.nih.gov/1425829

II. Bothin CG, Okada M, Midtvedt T (1999). Postsurgical adhesion formation in germfree and ex-germfree rats--a study using three scoring scales. J Invest Surg. 12(3): 147-50.
https://pubmed.ncbi.nlm.nih.gov/10421516

III. Okada M, Bothin C, Blomhoff R, Kanazawa K, Midtvedt T (1999). Vitamin A deficiency impairs colonic healing but not adhesion formation in germ-free and conventional rats. J Invest Surg. 12(6): 319-25.
https://pubmed.ncbi.nlm.nih.gov/10630395

IV. Bothin C, Okada M, Midtvedt T, Perbeck (2001). The intestinal flora influences adhesion formation around surgical anastomoses. Br J Surg. 88(1): 143-5.
https://pubmed.ncbi.nlm.nih.gov/11136328

V. Bothin C, Perbeck L, Midtvedt T (2002). Antibiotic treatment can decrease intra-abdominal adhesion formation. [Submitted]