I have a friend who suffered from 'auto-brewery syndrome' last year. From wikipedia:

Auto-brewery syndrome, also known as gut fermentation syndrome, is a rare medical condition in which intoxicating quantities of ethanol are produced through endogenous fermentation within the digestive system. One gastrointestinal organism, Saccharomyces cerevisiae, a type of yeast, has been identified as a pathogen for this condition.

Now imagine an auto-brewery syndrome with this modified yeast...