Culture-independent analysis of desulfovibrios in the human distal colon of healthy, colorectal cancer and polypectomized individuals

The production of hydrogen sulphide, an end product of metabolism by the sulphate-reducing bacteria (SRB) has been cited as a potential aetiological agent in gastrointestinal disease. Quantitative PCR (Q-PCR) assays to enumerate desulfovibrios from two gastrointestinal disease groups: colorectal cancer (CRC) n =27 and polypectomized individuals (PP) n =27, and two healthy control groups, elderly (H1) n =8 and young adults (H2) n =30 was performed. Analysis of Desulfovibrio sp. diversity using the dissimilarity sulphite reductase ( dsrAB ) gene as a molecular marker was also undertaken. Q-PCR detected Desulfovibrio sp. in all samples and no significant difference was observed for PP, H1, H2 with gene copy numbers of Desulfovibrio sp. averaging at 10⁶ g⁻¹ of faeces. Significantly reduced numbers of Desulfovibrio sp. were observed for CRC (10⁵ g⁻¹) compared with both PP and H2 groups ( P <0.05). Diversity analysis indicated that a low Desulfovibrio sp. diversity and the predominance of Desulfovibrio piger was a feature of both healthy and disease groups. In addition, a dsrAB gene sequence distantly related to a Gram-positive SRB was also recovered, highlighting the importance of cultivation-independent techniques for furthering our understanding of the diversity of the human gastrointestinal ecosystem.