SIBO is a condition in which there is an increase in the number of bacteria in the small bowel, and typically includes an overgrowth of coliform bacteria which are normally found in the colon. These ferment carbohydrates into gas (which can be measured using the lactulose breath test (LBT)), and the SIBO hypothesis proposes that it is this expansion of bacteria in the small bowel that leads to IBS symptoms including bloating, abdominal discomfort and changes in stool form. The antibiotic rifaximin is used to treat IBS-D, and has been shown to normalize the LBT in 70% of subjects. Despite this success, symptoms such as SIBO tend to recur, usually within 4 months of finishing the antibiotic treatment. Therefore, there remains a significant need to identify therapeutic agents which can maintain the health of subjects with IBS and SIBO and increase the duration of benefit in subjects with IBS and SIBO following antibiotic treatment.