A shift to Gram-negative bacteria in the intestinal microflora contributes to immunopathology of acute ileitis in the Toxoplasma gondii-driven mouse model of small intestinal inflammation

Abstract number: 1134_02_151

Heimesaat M., Fischer A., Fuchs D., Goldenberg O., Jahn H., Dunay I., Schumann R., Moter A., Gescher D., Hahn H., Göbel U., Bereswill S., Liesenfeld O.

Objectives:

The normal gut microbiota triggers experimental colitis and large intestinal manifestations of human inflammatory bowel diseases (IBD). However, the availability of animal models for the study of ileitis is limited. Thus, only little is known hitherto in small intestinal IBD. Recently, parasite-induced ileitis in the mouse, mimicking characteristics of ileitis in human IBD, was proposed as a model for Crohn's disease (CD). Oral infection of susceptible C57BL / 6 mice with Toxoplasma gondii induces a severe Th1-type immunopathology, which is restricted to the terminal ileum. In order to unravel the mechanisms underlying ileitis, we used this model to monitor microflora changes during ileal inflammation and determined contributions of the gut microbiota to ileal disease.

Methods:

C57BL / 6 mice were infected perorally with 100 cysts of T. gondii (ME49 strain). Ciprofloxacin, metronidazole, ciprofloxacin plus metronidazole (each 50 mg / kg body weight / d, p.o.), piperacillin plus tazobactam (200 mg/kg body weight/d, i.p.) were applied from day 0 until day 8 after T. gondii-infection. The ileal bacterial flora was analysed on day 8 p.i. by microbiological and molecular methods (16S rDNA-targeted denaturing gel electrophoresis (DGGE), sequencing of clone libraries).

Results:

Microbiological and molecular approaches revealed that ileal inflammation leads to an increased total bacterial load and to drastic changes in the flora composition. In the acute stage of disease, the grampositive cocci and rods - predominant in the ilea of healthy mice - are displaced by gramnegatives, identified as Escherichia coli and Bacteroides sp., respectively. Antibacterial treatment (ciprofloxacin, metronidazole, a combination of both, or piperacillin plus tazobactam) ameliorated disease symptoms and reduced ileal inflammation. This was also seen in SPF-mice colonized by only one grampositive bacterial species.

Conclusions:

The fact that gramnegative bacteria accumulate during acute ileitis and contribute profoundly to intestinal inflammation is well in line with similar observations in experimental colitis and in human IBD. This provides evidence that gut flora modulation is a valuable therapeutical strategy for IBD treatment. Finally, the contribution of gut microbiota to ileal disease supports the use of the parasite-induced small intestinal inflammation as a model for IBD research.