Any minor or unwanted substance introduced into the environment that can have undesired effects.
Any prokaryotic metabolite produced during a metabolic reaction in bacteria.
A xenobiotic (Greek, xenos "foreign"; bios "life") is a compound that is foreign to a living organism. Principal xenobiotics include: drugs, carcinogens and various compounds that have been introduced into the environment by artificial means.
A substance that kills or slows the growth of microorganisms, including bacteria, viruses, fungi and protozoans.
(via macrolide antibiotic )