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

Description

Strains of the Bacillus cereus (Bc) group are sporulating bacteria commonlyassociated with foodborne outbreaks. Spores are dormant cells highly resistantto extreme conditions. Nevertheless, the pathological processes associatedwith the ingestion of either vegetative cells or spores remain poorlyunderstood. Here, we demonstrate that while ingestion of vegetative bacterialeads to their rapid elimination from the intestine of Drosophila melanogaster,a single ingestion of spores leads to the persistence of bacteria for at least 10days. We show that spores do not germinate in the anterior part of the intestinewhich bears the innate immune defenses. Consequently, spores reach theposterior intestine where they germinate and activate both the Imd and Tollimmune pathways. Unexpectedly, this leads to the induction of amidases,which are negative regulators of the immune response, but not to antimicrobialpeptides. Thereby, the local germination of spores in the posteriorintestine dampens the immune signaling that in turn fosters the persistenceof Bc bacteria. This study provides evidence for how Bc spores hijack theintestinal immune defenses allowing the localized birth of vegetative bacteriaresponsible for the digestive symptoms associated with foodborne illnessoutbreaks.

Abstract

International audience

Additional details