Just in time for Halloween: a recently-published study in mBio discusses the 2014 outbreak of Listeria monocytogenes tied to caramel apples. There’s not enough water in caramel and an apple is too acidic to support this bacterium, so how did this outbreak occur? From the study: “Our findings suggest that the 2014 listeriosis outbreak associated with caramel-coated apples can be explained by growth of L. monocytogenes occurring at the interface between two foods which, by themselves, are inhibitory to pathogen growth.”