Ingestion of Bacillus cereus spores dampens the immune response to favor bacterial persistence

Abstract

Spores are considered as dormant entities highly resistant to extreme conditions. Among them, Bacillus cereus spores are commonly associated with foodborne outbreaks. Nevertheless, the pathological processes associated with spore ingestion and germination remain poorly understood. Here, we show that while ingestion of vegetative bacteria leads to their elimination from the midgut and small intestines of Drosophila and mice, respectively, a single ingestion of spores leads to the persistence of bacteria for at least 10 days. Using Drosophila genetics, we demonstrate that spores escape the innate immune response of the anterior midgut. Once in the posterior midgut, spores germinate, and the vegetative cells dampen the immune signaling through the induction of amidases which are negative regulators of the immune response. This study provides evidence for how B. cereus spores hijack the intestinal immune defenses allowing the localized birth of vegetative bacteria responsible for the digestive symptoms associated with foodborne illness outbreaks.