Host Stress Drives Salmonella Recrudescence.

Host stress is well known to result in flare-ups of many bacterial, viral and parasitic infections. The mechanism by which host stress is exploited to increase pathogen loads, is poorly understood. Here we show that Salmonella enterica subspecies enterica serovar Typhimurium employs a dedicated mechanism, driven by the scsA gene, to respond to the host stress hormone cortisol. Through this mechanism, cortisol increases Salmonella proliferation inside macrophages, resulting in increased intestinal infection loads in DBA/2J mice. ScsA directs overall Salmonella virulence gene expression under conditions that mimic the intramacrophagic environment of Salmonella, and stimulates the host cytoskeletal alterations that are required for increased Salmonella proliferation inside cortisol exposed macrophages. We thus provide evidence that in a stressed host, the complex interplay between a pathogen and its host endocrine and innate immune system increases intestinal pathogen loads to facilitate pathogen dispersal.