Virulence priming of Listeria monocytogenes inside replication-permissive endolysosomes

Abstract

Listeria monocytogenes (Lm), the foodborne pathogen responsible for listeriosis, is well-known for its intracellular lifestyle. After entering epithelial cells, it can evade within minutes from its internalization vacuole into the cytosol, or transiently co-opt and replicate within endomembrane compartments termed epithelial Spacious ListeriA-containing Phagosomes (eSLAPs). Although eSLAPs display endolysosomal features, we bring evidence that they lack cathepsin D activity and are permeated. Indeed, sustained eSLAP membrane perforation by listeriolysin O is crucial for accommodating bacterial growth and vacuole expansion. Conversely, we show that Lm broad range phospholipase C PlcB is the main escape factor from eSLAPs. Unexpectedly, we find that Lm PrfA-dependent cytosolic virulence program is primed inside eSLAPs. As a consequence, the bacteria released from eSLAPs are pre-equipped with the actin assembly-inducing protein ActA and can recruit actin faster. We propose that a delayed access to the cytosol benefit eSLAP-transiting bacteria by favoring their dissemination or evasion from xenophagy.