An antimicrobial is an agent that kills microorganisms or stops their growth. Antimicrobial medicines can be grouped according to the microorganisms they act primarily against. Antibiotics are used against bacteria and antifungals are used against fungi. Agents that kill microbes are called microbicidal while those that merely inhibit their growth are called biostatic. The use of antimicrobial medicines to treat infection is known as antimicrobial chemotherapy, while the use of antimicrobial medicines to prevent infection is known as antimicrobial prophylaxis. The main classes of antimicrobial agents are disinfectants such as nonselective antimicrobials such as bleach, which kill a wide range of microbes on non-living surfaces to prevent the spread of illness, antiseptics which are applied to living tissue and help reduce infection during surgery and antibiotics which destroy microorganisms within the body.