Gut microorganisms communicate using autoinducer 2 (AI-2). Treatment with antibiotics can alter the composition of the microbiota, which can be ameliorated by modulating levels of AI-2. Eukaryotic cells produce cytokines, such as interleukin-8 (IL-8), in response to AI-2. Hormones (adrenaline and noradrenaline) and AI-2 mimics are produced by the host and can be detected by bacteria. Quorum sensing can alter phenotypic heterogeneity among isogenic members of a bacterial population, which affects virulence-related traits, such as biofilm formation.