For the lazy:

A new study ... from the University of Chicago found that one of the most common classes of lantibiotics has potent effects both against pathogens and against the commensal gut bacteria that keep us healthy. Nisin is a popular lantibiotic used in everything from beer and sausage to cheese and dipping sauces. ...microbes in the human gut produce similar lantibiotics too. “Nisin is, in essence, an antibiotic that has been added to our food for a long time, but how it might impact our gut microbes is not well studied,... He... mined a public database of human gut bacteria genomes and identified genes for producing six different gut-derived lantibiotics that closely resemble nisin, four of which were new. Then...they produced versions of these lantibiotics to test their effects on both pathogens and commensal gut bacteria. ...“This study ...show that gut commensals are susceptible to lantibiotics, and are sometimes more sensitive than pathogens,” Zhang said. “With the levels of lantibiotics currently present in food, it’s very probable that they might impact our gut health as well.”

tl;dr: we put a preservative in food that our bodies make in our guts. They can kill bacteria in our guts. Nobody knows if this is good or bad.