See also natural products.

Compounds produced by bacteria, fungi or plants that are not directly involved in normal growth, development or reproduction.

Secondary metabolites have a variety of functions, often linked to the protection of an organism against environmental stressors or predation. Many have activity against bacteria, including those that cause bacterial infections in humans. Multiple antibiotics in common use have been developed from secondary metabolites, such as tetracycline and lipopeptide antibiotics.

Genomic studies suggest that organisms that produce secondary metabolites with antimicrobial properties have the potential to make a wide range of such compounds. Activating the genes responsible for the biosynthesis of such compounds is a possible approach to identify new antibiotics.