Definition: The word "antibacterial" refers to a substance that prevents bacteria from multiplying. Antimicrobial agents are used in medicine to prevent or treat infections. They're not harmful to humans, so they may be used on animals but should never be administered directly to people. Definition: A chemical compound that inhibits the growth and reproduction of bacteria. The word "antibiotic" is used in medicine to refer to any substance that kills or prevents the growth or reproduction of bacteria. Antimicrobial agents are useful for treating infections, but they must not harm healthy cells. The word "antibody" refers to a protein found on the surface of white blood cells (such as those seen in the body's immune system) that help fight off harmful organisms. Definition: A substance produced by an antibody and used to identify foreign substances, such as viruses or bacteria.