Disinfectant

Disinfectants are antimicrobial agents that are applied to non-living objects to destroy microorganisms, the process of which is known as disinfection. Disinfectants should generally be distinguished from antibiotics that destroy microorganisms within the body, and from antiseptics, which destroy microorganisms on living tissue. Sanitisers are high level disinfectants that kill over 99.9% of a target microorganism in applicable situations. Very few disinfectants and sanitisers can sterilise (the complete elimination of all microorganisms), and those that can depend entirely on their mode of application. Bacterial endospores are most resistant to disinfectants, however some viruses and bacteria also possess some tolerance.

Properties
A perfect disinfectant would offer complete sterilisation, without harming other forms of life, be inexpensive, and non-corrosive. Unfortunately ideal disinfectants do not exist. Most 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 indoors 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), whilst others kill a smaller range of disease-causing organisms but are preferred for other properties (they may be non-corrosive, non-toxic, or inexpensive).

The disinfecting properties of sunlight (ultra-violet) are powerful. Rather than total reliance on chemicals, basic hygiene - a pillar of food safety - is important in the fight against bacteria since they 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 is important in prevention of foodborne illness.

Alcohols
Alcohols, usually ethanol or isopropanol, are wiped over benches and skin and allowed to evaporate for quick disinfection. They have wide microbiocidal activity, are non corrosive, but can be a fire hazard. They also have limited residual activity due to evaporation, which results in brief contact times, and have a limited activity in the presence of organic material. Alcohols are more effective combined with purified water&mdash;70% isopropyl alcohol or 62% ethyl alcohol is more effective than 95% alcohol. Alcohol is not effective against fungal or bacterial spores.

Aldehydes
Aldehydes, such as Glutaraldehyde, have a wide microbiocidal activity and are sporocidal and fungicidal. They are partly inactivated by organic matter and have slight residual activity.

Halogens

 * Chloramine is used in drinking water treatment instead of chlorine because it produces fewer disinfection byproducts.


 * Chlorine is used to disinfect swimming pools, and is added in small quantities to drinking water to reduce waterborne diseases.


 * Hypochlorites (Sodium hypochlorite), often in the form of common household bleach, are used in the home to disinfect drains, and toilets. Other hypochlorites such as calcium hypochlorite are also used, especially as a swimming pool additive. Hypochlorites yield an aqueous solution of hypochlorous acid that is the true disinfectant. Hypobromite solutions are also sometimes used.


 * Iodine is 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. 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.


 * Chloramine-T is antibacterial even after the chlorine has been spent.

Oxidizing agents
Oxidizing agents act by oxidising the cell membrane of microorganisms, which results in a loss of structure and leads to cell lysis and death.


 * Chlorine dioxide is 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. Sodium chlorite, sodium chlorate, and potassium chlorate are used as precursors for generating chlorine dioxide.


 * Hydrogen peroxide is 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 a hydroxyl free radical. It is the damage caused by the oxygen free radical that kills bacteria. However, recent studies have shown hydrogen peroxide to be toxic to growing cells as well as bacteria; its use as an antiseptic is no longer recommended.


 * Ozone is a gas that can be added to water for sanitation.


 * Acidic Electrolyzed Water is a strong oxidising solution made from the electrolysis of ordinary tap water in the presence of a specific amount of salt, generally sodium chloride. Anolyte has a typical pH range of 3.5 to 8.5 and an Oxidation-Reduction Potential (ORP) of +600 to +1200 mV. The most powerful anolyte disinfecting solution is that produced at a controlled 5.0 to 6.3 pH where the predominant oxchlorine species is hypochlorous acid. This environmentally-responsible disinfectant is highly efficacious against bacteria, fungus, mold, spores and other micro-organisms, in very short contact times. It may be applied as liquid, fog or ice.


 * Peracetic acid is a disinfectant produced by reacting hydrogen peroxide with acetic acid. It is broadly effective against microorganisms and is not deactivated by catalase and peroxidase, the enzymes which break down hydrogen peroxide. It also breaks down to food safe and environmentally friendly residues (acetic acid and hydrogen peroxide), and therefore can be used in non-rinse applications. It can be used over a wide temperature range (0-40°C), wide pH range (3.0-7.5), in clean-in-place (CIP) processes, in hard water conditions, and is not affected by protein residues.


 * Potassium permanganate (KMnO4) is a red crystalline powder that 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.


 * Potassium peroxymonosulfate, the principal ingredient in Virkon, is a wide-spectrum disinfectant used in labs. Virkon 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.

Phenolics
Phenolics are active ingredients in some household disinfectants. They are also found in some mouthwashes and in disinfectant soap and handwashes.


 * Phenol is probably the oldest known disinfectant as it was first used by Lister, when it was called carbolic acid. It is rather corrosive to the skin and sometimes toxic to sensitive people.


 * O-phenylphenol is often used instead of Phenol, since it is somewhat less corrosive.


 * Chloroxylenol is the principal ingredient in Dettol, a household disinfectant and antiseptic.


 * Hexachlorophene is a phenolic that was once used as a germicidal additive to some household products but was banned due to suspected harmful effects.


 * Thymol, derived from the herb thyme, is the active ingredient in the only 100% botanical disinfectant with an EPA registration (#74771-1), Benefect. Registered as "broad spectrum," or hospital-grade, it is also the only disinfectant with a green certification, Environmental Choice.

Quaternary ammonium compounds
Quaternary ammonium compounds (Quats), such as benzalkonium chloride, are a large group of related compounds. Some have been used as low level disinfectants. 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 also be effective disinfectants against enveloped viruses.

Other
The biguanide polymer polyaminopropyl biguanide is specifically bactericidal at very low concentrations (10 mg/l). It has an unique method of action: the polymer strands are incorporated into the bacterial cell wall, which disrupts the membrane and reduces its permeability, which has an lethal effect to bacteria. It is also known to bind to bacterial DNA, alter its transcription, and cause lethal DNA damage. It has very low toxicity to higher organisms such as human cells, which have more complex and protective membranes.

High-intensity shortwave ultraviolet light can be used for disinfecting smooth surfaces such as dental tools, but not porous materials that are opaque to the light such as wood or foam. Ultraviolet light fixtures are often present in microbiology labs, and are activated only when there are no occupants in a room (e.g., at night).

Relative effectiveness of disinfectants
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.

Home disinfectants
By far the most cost-effective home disinfectant is the commonly used chlorine bleach (a 5% solution of Sodium hypochlorite) which is effective against most common pathogens, including such difficult organisms tuberculosis (mycobacterium tuberculosis), hepatitis B and C, fungi, and antibiotic-resistant strains of staphylococcus and enterococcus. It even has some disinfectant action against parasitic organisms. Positives are that it kills the widest range of pathogens of any inexpensive disinfectant; it is extremely powerful against viruses and bacteria at room temperature; it is commonly available and inexpensive; and it breaks down quickly into harmless components (primarily table salt and oxygen). Negatives are that it is caustic to the skin and eyes, especially at higher concentrations; like many common disinfectants, it degrades in the presence of organic substances; it has a strong odor; it is not effective against giardia lamblia and cryptosporidium; and extreme caution must be taken not to combine it with ammonia or any acid (such as vinegar as this may cause noxious gases to be formed). The best practice is not to add anything to household bleach except water. Dilute bleach can be tolerated on the skin for a period of time by most persons, as witnessed by the long exposure to extremely dilute "chlorine" (actually sodium or calcium hypochlorite) many children get in swimming pools.

To use chlorine bleach effectively, the surface or item to be disinfected must be clean. In the bathroom, special caution must be taken to wipe up urine. A 1 to 20 solution in water is effective simply by being wiped on and left to dry. The user should wear rubber gloves and, in tight airless spaces, goggles. If parasitic organisms are suspected, it should be applied at 1 to 1 concentration, or even undiluted; extreme caution must be taken to avoid contact with eyes and mucous membranes. Protective goggles and good ventilation are mandatory when applying concentrated bleach.

Where one does not want to risk the corrosive effects of bleach, alcohol-based disinfectants are reasonably inexpensive and quite safe. The great drawback to them is their rapid evaporation; sometimes effective disinfection can be obtained only by immersing an object in the alcohol.