Quorum sensing in Clostridium difficile: analysis of a luxS-type signalling system

The increasing incidence of Clostridium difficile-associated disease, and the problems associated with its control, highlight the need for additional countermeasures. The attenuation of virulence through the blockade of bacterial cell-to-cell communication (quorum sensing) is one potential therapeutic target. Preliminary studies have shown that C. difficile produces at least one potential signalling molecule. Through the molecule s ability to induce bioluminescence in a Vibrio harveyi luxS reporter strain, it has been shown to correspond to autoinducer 2 (AI-2). In keeping with this observation, a homologue of luxS has been identified in the genome of C. difficile. Adjacent to luxS(Cd) a potential transcriptional regulator and sensor kinase, rolA and rolB, have been located. RT-PCR has been used to confirm the genetic organization of the luxS(Cd) locus. While AI-2 production has not been blocked so far using antisense technology, AI-2 levels could be modulated by controlling expression of the putative transcriptional regulator rolA. RolA, therefore, acts as a negative regulator of AI-2 production. Finally, it has been shown that the exogenous addition of AI-2 or 4-hydroxy-5-methyl-3(2H) furanone has no discernible effect on the production of toxins by C. difficile.