Lipid Species in the GI Tract are Increased by the Commensal Fungus and Decrease the Virulence of .

Prior antibiotic treatment is a risk factor for infection (CDI); the commensal gut microbiota plays a key role in determining host susceptibility to the disease. Previous studies demonstrate that the pre-colonization of mice with a commensal fungus, , protects against a lethal challenge with spores. The results reported here demonstrate that the cecum contents of antibiotic-treated mice with colonization contained different levels of several lipid species, including non-esterified, unsaturated long-chain fatty acids compared to non--colonized mice. Mice fed olive oil for one week and challenged with spores showed enhanced survival compared to PBS-fed mice. The amount of olive oil administered was not sufficient to cause weight gain or to result in significant changes to the bacterial microbiota, in contrast to the effects of a high-fat diet. Furthermore, the direct exposure of bacteria in laboratory culture to the unsaturated fatty acid oleic acid, the major fatty acid found in olive oil, reduced the transcription of genes encoding the toxins and reduced the survival of bacteria in the post-exponential phase. Therefore, the effects of on the metabolite milieu contributed to the attenuation of virulence.