Bacterial vampirism mediated through chemotaxis.

Severe bacterial infections of the gastrointestinal (GI) tract instigate GI hemorrhaging that can lead to bacteremia, sepsis, and death. Pathogens preferentially colonize sites of injury, delaying healing and exacerbating tissue damage, but the underlying mechanisms are not well understood. We find that Enterobacteriaceae species are remarkably sensitive to human serum and perceive femtoliter quantities as a potent attractant. This behavior is driven by chemotaxis and the Tsr chemoreceptor, which recognizes L-serine present in serum. By studying the crystal structure of Salmonella Typhimurium Tsr, we identified a recognition motif for L-serine and found similar Tsr homologues in various Enterobacteriaceae species, including World Health Organization priority pathogens. Our analyses of Escherichia and Citrobacter bacteria, which also possess Tsr, confirm that these species exhibit chemoattraction to serum. We have coined the term 'vampirism' to describe this pathogenesis strategy and suggest it plays a role in injury tropism and increases the risk of bacteremia.