Colonic fermentation as affected by antibiotics and acidic pH: Application of an in vitro model.

Antimicrobial substances such as vancomycin or metronidazole suppress normal gut flora, thereby preventing physiological fermentation of colonic substrates that may promote mucosal inflammation. This study was designed to establish an in vitro model of microbial metabolism in the colon under control and disturbed conditions (acidic pH) to investigate specific effects of vancomycin and metronidazole on the production of short chain fatty acids (SCFA), which play a pivotal role in maintaining homeostasis in the colon. The experiments were carried out with the colon simulation technique (Cositec) representing an in vitro model for the semi-continuous incubation of defined colon contents. Inocula and fermentable substrates were sampled from cecal contents of fistulated pigs. Disturbed microbial metabolism was generated by reduction of pH in the fermentation vessels from 6.7 to 5.8 and 5.1. In general, application of either vancomycin or metronidazole resulted in a significant decrease of SCFA production rates indicating substantial disturbance of the homeostasis of microbial metabolism. With low doses of vancomycin acetate and butyrate production rates were reduced and with high doses of the antibiotic propionate production was inhibited to a greater extent. Treatment with metronidazole inhibited butyrate production almost completely. Similarly, low pH caused a reduction in total SCFA production, which was mainly due to respective decrease of acetate synthesis. Metronidazole effects were not consistently changed at low pH. The Cositec system provides an excellent facility to test the effects of different antibiotics under defined conditions. In this study, both vancomycin and metronidazole affected microbial metabolism to a considerable extent. Both substances may thus be responsible for disturbances of colon function in vivo.