Antimicrobial is the name for a chemical that either kills or prevents the growth of microbes ('bugs' or 'germs') such as bacteria, viruses, fungi or protozoa. Some antimicrobials are produced by bugs themselves (e.g. penicillin is produced by the penicillium mould), others are designed in the laboratory. Different bugs are susceptible to different antimicrobials e.g. the penicillium mould is not killed by the penicillin it produces, but some bacteria are susceptible to penicillin.