Signaling pathways are required for bacterial biofilm formation and antimicrobial resistance. Among them, quorum sensing (QS) and c-di-GMP signaling are the best characterized. QS is a widely distributed intercellular signaling mechanism by which microorganisms regulate gene expression in response to small diffusible signaling molecules. Bacteria have developed oligopeptides, N-acyl homoserine lactones (HSLs), and autoinducer-2 as signal molecules. When the QS signal molecules reach a local threshold concentration, they can interact with specific receptors and impact the expression of hundreds of genes. Many of the QS-regulated genes (motility, biosurfacant synthesis, EPS synthesis) are required for the biofilm formation and antibiotic resistance of various bacterial species.

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