Substances that destroy or inhibit the growth of microorganisms, particularly disease-producing bacteria and fungi. Antibiotics are obtained from microorganisms (especially moulds) or synthesized. Common antibiotics include the penicillins, streptomycin, and tetracyclines. They are used to treat various infections but tend to weaken the body’s natural defence mechanisms and can cause allergies. Overuse of antibiotics leads to the development of resistant strains of microorganisms, such as methicillin-resistant Staphylococcus aureus (MRSA), with the consequent need to develop new and effective antibiotics.

https://medlineplus.gov/antibiotics.html#cat1 Information about the use and abuse of antibiotics and the search for new ones