- To evaluate the clinical response (clinical cure) rates of patients with mild and moderate C. difficile infections to different LFF571 dose regimens and total daily doses adminisitered orally for 10 days. - To characterize the dose-response relationship of different dose regimens and total daily doses of LFF571. - To assess the safety and tolerability of different LFF571 dose regimens and total daily doses administered orally for 10 days to C. difficile infected patients.