Indole is an aromatic heterocyclic organic compound. It has a bicyclic structure,
consisting of a six-membered benzene ring fused to a five-membered nitrogen-containing
pyrrole ring. Indole is widely distributed in the natural environment and can be produced by a
variety of bacteria. As an intercellular signal molecule, indole regulates various aspects of
bacterial physiology, including spore formation, plasmid stability, and resistance to drugs,
biofilm formation, and virulence. The amino acid tryptophan is an indole derivative and the
precursor of the neurotransmitter serotonin.