Clostridium difficile-associated diarrhoea (CDAD) is the most common hospital-acquired diarrhoea, and is a major type of gastroenteritis infection in nursing homes and facilities for the elderly. In this study the antimicrobial activity of the two-component lantibiotic, lacticin 3,147, against a range of genetically distinct C. difficile isolates was studied. The bacteriocin exhibited an MIC(50) of 3.6 microg ml(-1) for 10 genetically distinct C. difficile strains isolated from healthy subjects, inflammatory bowel disease patients and culture collection strains. In time-kill studies, 10(6) c.f.u. ml(-1) C. difficile ATCC 42,593 and CDAD isolate DPC 6,220 were killed within 120 or 20 min incubation, respectively, at a concentration of 6 microg lacticin ml(-1). Interestingly, addition of lacticin 3,147 to exponentially growing cells of C. difficile ATCC 43,593 caused rapid lysis of the cells after an initial lag phase, as measured by the concomitant release of the intracellular enzyme, acetate kinase. The addition of a food-grade, milk-based lacticin containing powder to faecal fermentation demonstrated that lacticin is effective in completely eliminating 10(6) c.f.u. C. difficile ml(-1) from a model faecal environment within 30 min when present at concentrations as low as 18 microg ml(-1). While other culturable microflora such as total anaerobes, bacteroides, total non-spore-forming anaerobes and total Gram-negative anaerobes were unaffected, populations of lactobacilli and bifidobacteria were reduced by 3 log cycles at bacteriocin levels sufficient to eliminate over 10(6) C. difficile. In light of these findings, the potential of lacticin 3,147 for treatment of CDAD is discussed.