Gut osmolarity: A key environmental cue initiating the gastrointestinal phase of Listeria monocytogenes infection?

In addition to the severe invasive systemic disease of listeriosis, recent evidence suggests that the Gram-positive intracellular bacterial pathogen Listeria monocytogenes is also a causative agent of febrile gastroenteritis. We examined the listerial response to stresses normally encountered in the upper small intestine and demonstrate that osmotic stress appears to be at the top of the hierarchy of stress responses during gastrointestinal residence. Furthermore, we suggest that the increased osmolarity of the gastrointestinal lumen may be interpreted as an environmental cue signalling gut entry and that the underlying genetic element governing this response is the alternative stress sigma factor σ^B.