Effect of different carbohydrates on in vitro fermentation activity and bacterial numbers of porcine inocula under osmotic stress conditions

Abstract

The bacteria of the intestine have to cope with varying osmotic conditions in their ecosystem. In this in vitro study, the modified Hohenheim gas test (HGT) was used to determine fermentation activity and bacterial composition of pig's faecal microbial inoculum, when fermenting different carbohydrates (inulin, corn starch, potato starch, cellulose, pectin), under normal buffered and osmotic stress conditions (elevated medium salinity). After 24 h of fermentation, gas, ammonia and short-chain fatty acid (SCFA) production was measured, and the cell numbers of total eubacteria, Lactobacillus spp., Bifidobacterium spp. and enterobacteria were analysed, using real-time polymerase chain reaction. There was a significant reduction in gas production after 24 h when comparing osmotic stress conditions with normal buffered conditions, and there were also differences among carbohydrates under both conditions. The content of SCFA was significantly lower when comparing osmotic stress with normal buffered conditions. Under osmotic stress, inulin and corn starch increased (p < 0.05) cell numbers of total eubacteria, while Bifidobacterium spp. and enterobacteria were higher (p < 0.05) when corn starch and pectin were fermented, respectively, in comparison to the other carbohydrates. The in vitro system of the modified HGT appears to be suitable to scrutinise effects of carbohydrates on the metabolic activity and composition of the microbial community under osmotic stress conditions, as they might occur during situations of osmotic diarrhoea.

Keywords:

• bacterial count
• carbohydrates
• fermentation products
• in vitro
• osmotic pressure
• pigs

Acknowledgements

The authors wish to thank H. Wilhelm Schaumann Foundation (Hamburg, Germany) for financial support of this work and for the provision of a scholarship to Franziska Rink. The technical assistance of Helga Terry, Helga Ott and the Weender team of the Institute of Animal Nutrition at the University of Hohenheim during the performance of the chemical analysis is highly appreciated. Special thanks go to Silke Roth for her great support in assisting with chemical analysis and real-time PCR and to Ingrid Neff for her help in preparing this manuscript.

Additional information

Notes on contributors

Rainer Mosenthin

This article was presented in part at the seventh symposium of gut microbiology, Aberdeen, Scotland, 23–25 June 2010 (“Porcine intestinal microbiota is affected by different carbohydrates and osmotic stress in vitro”).