The antibiotics are substances produced by the natural metabolic processes of spore-forming aerobic bacteria and fungi as their natural defense against other microorganisms. Among bacteria and fungi, bacterial genera outnumber the fungal genera in the production of antibiotics. The highest numbers of antibiotics are derived from bacterial genera Streptomyces and Bacillus and fungal genera Penicillium and Cephalosporium. These antibiotics are used to control the disease-causing bacteria.