Introduction Even though some students have trouble getting bacteria to grow, usually the problem is just the opposite. Bacteria and other microorganisms are found almost everywhere. Usually, microbial controls are used to avoid contamination of pure cultures, prevent infection, or treat existing diseases. A microbicidal effect kills microorganisms. A microbistatic effect prevents the reproduction of microorganisms.
Antiseptics are chemicals used on living tissues to inhibit the growth of microorganisms.
Disinfectants are chemicals used on nonliving surfaces to inhibit the growth of microorganisms. The ionized molecules may lose critical chemical and physical structures, or react with other molecules, making the biochemicals useless. Ultraviolet light does not have enough energy to cause ionization. UV causes damage to nucleic acids by inducing covalent bonds between adjacent thymine bases, resulting in thymine dimerization. The thymine dimers change the structure of DNA, preventing DNA replication and RNA transcription.