Histamine is a key mediator governing vital cellular processes in mammals beyond its decisive role in inflammation. Recent evidence implies additional actions in both eukaryotes and prokaryotes. Besides its function in host defense against bacterial infections, histamine elicits largely undefined actions in microorganisms that may contribute to bacteria-host interactions. Bacterial proliferation and adaptation are governed by sophisticated signal transduction networks, including the versatile two-component systems (TCSs) that comprise sensor histidine kinases and response regulators and rely on phosphotransfer mechanisms to exert their modulatory function. The AtoSC TCS regulates fundamental cellular processes such as short-chain fatty acid metabolism, poly-(R)-3-hydroxybutyrate (cPHB) biosynthesis and chemotaxis in Escherichia coli. The implication of exogenous histamine in the AtoSC-mediated cPHB biosynthesis and in E. coli chemotactic behavior is indicative of a putative function of histamine in bacterial physiology. The data raise questions on the significance of histamine actions in bacteria-host symbiosis, dysbiosis and pathogenicity as well as on the possible consequences upon therapeutic administration of histamine receptor-targeting agents and in particular ligands of the recently identified immunomodulatory H4 receptor.