Disinfectant is a chemical that kills microorganisms- bacteria, viruses, protozoa, or fungi. Disinfectants are also often called germicides. Strictly speaking, disinfectants are used to kill pathogenic, or disease-causing, organisms, while germicides kill all organisms; however, this distinction is not essential, and substances known as disinfectants are used as preservatives and deodorizers to kill nonpathogenic organisms. A distinction may also be made between disinfectants, which kill microorganisms on inanimate objects, and antiseptics, which kill organisms on living tissues. This distinction between disinfectants and antiseptics is not rigid, however, and many chemicals are suitable for both uses; in fact, the application of germicides to unbroken skin to prevent infection is usually called disinfection.
Disinfectants may also be divided according to the particular class of microorganisms that they affect; for example, bactericides kill bacteria, and viricides kill viruses. The term "disinfectant" is an old one, and it does not include antimicrobial substances that are produced by living cells, that is, antibiotics.
Types of Disinfectant
Hundreds of disinfectant chemicals are now available. They are found in many chemical classes and include phenolic compounds (phenols, cresols, halogenated phenols), alcohols (ethyl alcohol and propyl alcohol), aldehydes (formaldehyde), acids (propionic acid and benzole acid), halogenated compounds (chlorine, hypochlorite, iodine, and organic iodine compounds), and the derivatives of heavy metals (copper and mercury salts, organic mercurials).
An important group of disinfectants synthesized in more recent years comprises the surface-active agents such as benzalkonium and cetylpyridinium. These disinfectants are similar to modern detergents. They combine penetrating and cleansing power with high germicidal potency and are widely used as hospital and home disinfectants. Many disinfectant cleansing preparations now contain a surface-active agent.
Iodine is a particularly effective disinfectant and antiseptic that has many desirable properties. Newly developed germicides that release iodine in solution have important industrial uses, particularly in dairies and other food-handling establishments.
Properties and Action
Several properties are desirable in disinfectants. To be efficient in killing microorganisms, disinfectants should have a broad antimicrobial spectrum, that is, the ability to destroy all types of microorganisms, including spore forms of bacteria and fungi, and rapid killing power. They should also have high potency (so that only small amounts are necessary), chemical stability and nonreactivity, and high penetrating power (low surface tension). The absence of staining, corrosive, or irritating properties is another desirable characteristic.
Of all the properties desirable for disinfectants, the most important is germicidal potency and speed of action. Great progress has been made in improving the methods of testing germicides, and some germicides that gained popularity as potential household disinfectants (e.g., the mercury compounds) have been found merely to inhibit bacterial growth rather than to kill the microorganisms. In modern testing procedures each of the desired properties is evaluated, and certain disinfectants are found to be best suited for specific uses.
The various disinfectant substances act differently. Many are protoplasmic poisons and are therefore toxic not only to microorganims but to all living tissues. The potential toxicity to man and animals of these disinfectants must be considered before they are widely used. A few other germicides are relatively harmless to man in doses that have effective antimicrobial concentrations. Among these are the food preservatives such as propionic and benzoic acids.