methanogens and sulfate-reducing bacteria.pdf

ORIGINAL ARTICLE Carriage, quantification, and predominance of methanogens and sulfate-reducing bacteria in faecal samples J.A. Stewart1, V.S. Chadwick1 and A. Murray2 1 Wakefield Gastroenterology Research Institute, Newtown, Wellington, New Zealand 2 Institute of Veterinary, Animal and Biomedical Sciences, Massey University, Palmerston North, New Zealand Introduction Methanogens and sulfate-reducing bacteria compete for a common substrate (H2) and have been linked to gastroin- testinal disorders (Pique et al. 1984; Roediger et al. 1997; Pimentel et al. 2003). Two methanogenic species, Met- hanobrevibacter smithii (Miller et al. 1982) and Metha- nosphaera stadtmaniae (Miller and Wolin 1985), have been isolated from the human intestine. These organisms carry out intestinal H2 gas disposal by producing CH4, and compete for this substrate with sulfate-reducing bac- teria, which generate H2S. Methanogens and sulfate-redu- cing bacteria are generally minor components of the human faecal microflora, and their rates of carriage vary among different ethnic groups (Gibson et al. 1988; Segal et al. 1988). Numbers of sulfate-reducing bacteria and concentrations of potentially toxic H2S have been repor- ted to be elevated in faeces from patients with ulcerative colitis (Pitcher and Cummings 1996; Pitcher et al. 2000). The prevalence of individuals who excrete methane in breath is higher amongst patients with colorectal cancer (Pique et al. 1984) and constipation-predominant irritable bowel syndrome (Pimentel et al. 2003). Breath methane tests and culture-based methods have traditionally been used to characterize methanogen popu- lations. However, breath tests lack sensitivity as methane is not liberated in the breath until the methanogens reach a density of 108 g)1 stool (Weaver et al. 1986) and the difficulty associated with culturing these slow-growing organisms make culture-based studies laborious. Sulfate- reducing bacteria have also traditionally been studied by culture me