Biofilms



Development of a fermentation system to model sessile bacterial populations in the human colon


H. M. Probert a1c1 and G. R. Gibson a1
a1 Food Microbial Sciences Unit, School of Food Biosciences, The University of Reading, Reading RG6 6BZ, UK

Article author query
probert h   [PubMed][Google Scholar] 
gibson g   [PubMed][Google Scholar] 

Abstract

A fermentation system was designed to model the human colonic microflora in vitro. The system provided a framework of mucin beads to encourage the adhesion of bacteria, which was encased within a dialysis membrane. The void between the beads was inoculated with faeces from human donors. Water and metabolites were removed from the fermentation by osmosis using a solution of polyethylene glycol (PEG). The system was concomitantly inoculated alongside a conventional single-stage chemostat. Three fermentations were carried out using inocula from three healthy human donors.

Bacterial populations from the chemostat and biofilm system were enumerated using fluorescence in situ hybridization. The culture fluid was also analysed for its short-chain fatty acid (SCFA) content. A higher cell density was achieved in the biofilm fermentation system (taking into account the contribution made by the bead-associated bacteria) as compared with the chemostat, owing to the removal of water and metabolites. Evaluation of the bacterial populations revealed that the biofilm system was able to support two distinct groups of bacteria: bacteria growing in association with the mucin beads and planktonic bacteria in the culture fluid. Furthermore, distinct differences were observed between populations in the biofilm fermenter system and the chemostat, with the former supporting higher populations of clostridia and Escherichia coli. SCFA levels were lower in the biofilm system than in the chemostat, as in the former they were removed via the osmotic effect of the PEG. These experiments demonstrated the potential usefulness of the biofilm system for investigating the complexity of the human colonic microflora and the contribution made by sessile bacterial populations.


Correspondence:
c1 Corresponding author: Dr H. M. Probert, Food Microbial Sciences Unit, School of Food Biosciences, The University of Reading, Whiteknights, PO Box 226, Reading, Berkshire RG6 6BZ, UK T 44 01189 357215, F 44 01189 357222, E h.m.carpenter@reading.ac.uk