What Are Disinfectants

From Wikipedia, the free encyclopedia.

Disinfection is the destruction of pathogenic and other kinds of microorganisms by physical or chemical means. Disinfectants are chemical substances used to destroy viruses and microbes (germs), such as bacteria and fungi, as opposed to an antiseptic which can prevent the growth and reproduction of various microorganisms, but does not destroy them. The ideal disinfectant would offer complete sterilization, without harming other forms of life, be inexpensive, and non-corrosive. Unfortunately ideal disinfectants do not exist. Many disinfectants are only able to partially sterilize. The most resistant pathogens are bacteria spores but some viruses and bacteria are also highly resistant to many disinfectants.

All disinfectants are also, by their very nature, potentially harmful (even toxic) to humans or animals. They should be treated with appropriate care. Most come with safety instructions printed on the packaging, which should be read in full before using the disinfectant. Most modern household disinfectants contain Bitrex, an exceptionally bitter substance designed to discourage ingestion, as an added safety measure. Those that are used in people's homes should never be mixed with other cleaning products as chemical reactions can occur. They are frequently used in hospitals, dental surgeries, kitchens and bathrooms to kill infectious organisms.

The choice of the disinfectant to be used depends on the particular situation. Some disinfectants have a wide spectrum (kill nearly all microorganisms). (In the UK there was a long running advert for Domestos bleach in which it was claimed that "Domestos kills all known germs Dead!"). Others kill a smaller range of disease-causing organisms but are preferred for other properties (they may not be corrosive, and relatively non-toxic to humans).

The disinfecting properties of sunlight (ultra-violet) are powerful. Basic hygiene, rather than total reliance on chemicals, is important in the fight against bacteria, which generally prefer a warm-moist-dark environment. There are arguments for creating or maintaining conditions which are not conducive to bacterial survival and multiplication, rather than attempting to kill them with chemicals. Bacteria have a very rapid multiplication rate, which enables them to 'evolve' rapidly. Should some bacteria survive a chemical attack, they give rise to the next generation. Thus they are able to develop resistance to hostile chemicals. For this reason, some question the wisdom of impregnating cloths, cutting boards and worktops in the home with bactericidal chemicals. Hygiene in is important in prevention of foodborne illness.

A Note On Terminology

Disinfectants destroy vegetative microbes (bacteria, fungi) and viruses on surfaces, medical equipment and other man-made objects. Antiseptics disinfect skin. Antibiotics either kill or interfere with the life cycle of bacteria inside the body. Substances which kill bacteria are said to have a bactericidal effect, while those which interfere with cell growth and reproduction are said to be bacteriostatic. Disinfectants and antiseptics are bactericidal (some disinfectants are bacteriostatic at low concentrations): antibiotics can be either bactericidal or bacteriostatic.

Sanitation refers to killing 99+ % of germs in applicable situations. Sanitisers are compounds that sanitise.

Common Disinfectants

Chlorine—Used to disinfect swimming pools, and is added in small quantities to drinking water to reduce waterborne diseases.
Chloramine—Used in drinking water treatment instead of chlorine because it produces less disinfection byproducts.
Chlorine dioxide—Used as an advanced disinfectant for drinking water to reduce waterborne diseases. In certain parts of the world, it has largely replaced chlorine because it forms fewer byproducts.
Dettol—Used to disinfect surfaces at home. It kills the majority of bacteria. It is one of the few disinfectants useful against viruses.
Sodium chlorite, sodium chlorate, and potassium chlorate have little disinfection effect but are used as precursors for generating chlorine dioxide.
Alcohol—Usually ethanol or isopropanol—Wiped over benches and skin and allowed to evaporate for quick disinfection. Alcohols are more effective combined with water, 70% alcohol is more active than 95% alcohol. Alcohol is not effective against bacterial spores.
Hydrogen peroxide—Used in hospitals to disinfect surfaces. It is sometimes mixed with colloidal silver. It is often preferred because it causes far fewer allergic reactions than alternative disinfectants. Also used in the food packaging industry to disinfect foil containers. A 3% solution is also used as an antiseptic. When hydrogen peroxide comes into contact with the catalase enzyme in cells it is broken down into water and an oxygen free radical. It is the damage caused by the oxygen free radical that kills bacteria. However, as recent studies have show hydrogen peroxide to be toxic to growing cells as well as bacteria, its use as an antiseptic is no longer recommended.
Iodine—Usually dissolved in an organic solvent or as Lugol's iodine solution. It is used in the poultry industry. It is added to the birds' drinking water. Iodine is rapidly neutralised by the presence of organic material, so surfaces must be cleaned prior to disinfection. Although no longer recommended because it increases scar tissue formation and increases healing time, tincture of iodine has also been used as an antiseptic for skin cuts and scrapes.
Ozone—a gas that can be added to water for sanitation.
Phenol and other phenolics—The active ingredient in most bottles of "household disinfectant". It is also to found in some mouthwashes and in disinfectant soap and handwashes. Phenol is probably the oldest disinfectant (used by Lister) and was called carbolic acid in the early days of antiseptics. Phenol is rather corrosive to the skin and sometimes toxic to sensitive people, so the somewhat less corrosive substitute phenolic o-phenylphenol is often used as part of a disinfectant formula. Hexachlorophene is a phenolic which was once used as a germicidal additive to some household products but was banned due to suspected harmful effects.
Potassium permanganate—Formula KMnO4. A red crystalline powder, it colours everything it touches, and is used to disinfect aquariums. It is also used widely in community swimming pools to disinfect ones feet before entering the pool. Typically, a large shallow basin of KMnO4/water solution is kept near the pool ladder. Participants are required to step in the basin and then go into the pool. Additionally, it is widely used to disinfect community water ponds and wells in tropical countries, as well as to disinfect the mouth before pulling out teeth. It can be applied to wounds in dilute solution; potassium permanganate is a very useful disinfectant.
Quaternary ammonium salts ("quats") such as benzalkonium chloride are a large group of related compounds. Some have been used as a low level disinfectant. They are effective against bacteria, but not against some species of Pseudomonas bacteria or bacterial spores. Quats are biocides which also kill algae and are used as an additive in large-scale industrial water systems to minimize undesired biological growth. Quaternary ammonium compounds can be effective disinfectants against enveloped viruses.
Hypochlorites—Sodium hypochlorite, often in the form of common household bleach, is used in the home to disinfect drains, and toilets. A dilute form is used under the brand name Milton to disinfect baby bottles. Other hypochlorites such as calcium hypochlorite are also used, especially as a swimming pool additive. Hypochlorite gives off free chlorine and it is the chlorine that is the true disinfectant. Hypobromite solutions are also sometimes used.
Toluene-also known as methylbenzene or phenylmethane is a clear, water-insoluble liquid with the typical smell of paint thinners, redolent of the sweet smell of the related compound benzene. It is an aromatic hydrocarbon that is widely used as an industrial feedstock and as a solvent.
Virkon—A wide-spectrum disinfectant used in labs. It kills bacteria, viruses, and fungi. It is used as a 1% solution in water, and keeps for one week once it is made up. It is expensive, but very effective, its pink colour fades as it is used up so it is possible to see at a glance if it is still fresh.
Septustin M—A wide-spectrum disinfectant used in labs and hospitals. It kills bacteria, viruses, and fungi. It is used as a 0.3-4% solution in water, and keeps for two weeks once it is made up. It is relatively inexpensive and very effective.

In addition to these methods high-intensity ultraviolet light can be used for disinfecting smooth surfaces, such as dental tools, but not porous materials that are opague to the light such as wood or foam.

Relative Effectiveness of Disfectants

One way to compare disinfectants is to compare how well they do against a known disinfectant and rate them accordingly. Phenol is the standard, and the corresponding rating system is called the "Phenol coefficient". The disinfectant to be tested is compared with phenol on a standard microbe (usually Salmonella typhi or Staphylococcus aureus). Disinfectants that are more effective than phenol have a coefficient > 1. Those that are less effective have a coefficient < 1.