Ethanol is created by the fermentation of sugars present in a given feedstock, usually corn here in the United States. Yeast must be kept healthy enough to munch on these sugars if a good batch of alcohol is going to be produced, and ethanol producers are apparently using antibiotics like penicillin and virginiamycin to ward off yeast-killing bacteria.
Not only can the use of these antibiotics promote the growth of new strains of bacteria, it may also have undesirable effects to the leftover distillers grain, which is generally sold off as livestock feed. Leftover antibiotics in this distillers grain is a potential safety hazard for the livestock, with some studies linking the use of distillers grain to elevated rates of E. coli in cattle. There's always something, isn't there?