Chemical disinfection is done with disinfectants which are antimicrobial agents applied to the indoor surfaces to destroy microorganisms that are living on the surface. Disinfection does not necessarily kill all microorganisms, especially resistant bacterial spores. Disinfection it is less effective than sterilization, which is an strong physical and/or chemical process that kills all types of life. Disinfectants are different from other antimicrobial agents such as antibiotics, which destroy microorganisms within the body, and antiseptics, which destroy microorganisms on living tissue. Disinfectants work by destroying the cell wall of microbes or interfering with their metabolism.
Sanitizers are substances that simultaneously clean and disinfect. Disinfectants are frequently used in hospitals, dental surgeries, kitchens, and bathrooms to kill infectious organisms. Bacterial endospores are most resistant to disinfectants, but some viruses and bacteria also possess some tolerance.
An ideal disinfectant would also offer complete and full microbiological sterilisation, without harming humans and useful form of life and noncorrosive. However, most disinfectants are also, by nature, potentially harmful (even toxic) to humans or animals. The choice of disinfectant to be used depends on the individual case. Some disinfectants have a wide spectrum (kill many different types of microorganisms), while others kill a smaller range of disease-causing organisms but are preferred for other properties (they may be non-corrosive, non-toxic, or inexpensive). If some bacteria will survive a chemical attack, they might give rise to new generations composed completely of bacteria that have resistance to the chemical used. Under a sustained chemical attack, the surviving bacteria in successive generations are increasingly resistant to the chemical used, and ultimately the chemical is rendered ineffective. The use of some antimicrobials such as triclosan may lead to antimicrobial resistance. The use of chlorine bleach and alcohol disinfectants does not cause antimicrobial resistance as it denatures the protein of the microbe upon contact.
This group comprises aqueous solution of chlorine, hypochlorite, or hypochlorous acid. Frequently, a concentration of < 1 ppm of available chlorine is sufficient to kill bacteria and viruses, spores and mycobacteria requiring higher concentrations.
Chlorine
Iodine
Acids and bases
Alcohol and alcohol plus Quaternary ammonium cation based compounds comprise a class of proven surface sanitizers and disinfectants approved by the EPA and the Centers for Disease Control for use as a hospital grade disinfectant. Alcohols are most effective when combined with distilled water to facilitate diffusion through the cell membrane; 100% alcohol typically denatures only external membrane proteins. A mixture of 70% ethanol or isopropanol diluted in water is effective against a wide spectrum of bacteria, though higher concentrations are often needed to disinfect wet surfaces. Additionally, high-concentration mixtures (such as 80% ethanol + 5% isopropanol) are required to effectively inactivate lipid-enveloped viruses (such as HIV, hepatitis B, and hepatitis C).
Aldehydes, such as formaldehyde and glutaraldehyde, have a wide microbiocidal activity and are sporicidal and fungicidal. They are partly inactivated by organic matter and have slight residual activity. Some bacteria have developed resistance to glutaraldehyde, and it has been found that glutaraldehyde can cause asthma and other health hazards, hence ortho-phthalaldehyde is replacing glutaraldehyde.
Oxidizing agents act by oxidizing the cell membrane of microorganisms, which results in a loss of structure and leads to cell lysis and death. A large number of disinfectants operate in this way. Chlorine and oxygen are strong oxidizers, so their compounds figure heavily here.
Phenolics are active ingredients in some household disinfectants. They are also found in some mouthwashes and in disinfectant soap and handwashes.
Quaternary ammonium compounds, such as benzalkonium chloride, are a large group of related compounds. Some concentrated formulations have been shown to be effective low-level disinfectants. Quaternary Ammonia at or above 200ppm plus alcohol solutions exhibit efficacy against difficult to kill non-enveloped viruses such as norovirus, rotavirus, or polio virus.
It is specifically bactericidal at very low concentrations (10 mg/l). It has a unique method of action: The polymer strands are incorporated into the bacterial cell wall, which disrupts the membrane and reduces its permeability, which has a 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.
It is a registered disinfectant. Due to its natural and environmental profile, it has gained importance in the market.
Air disinfectants are typically chemical substances capable of disinfecting microorganisms suspended in the air. An air disinfectant must be dispersed either as an aerosol or vapour at a sufficient concentration in the air to cause the number of viable infectious microorganisms to be significantly reduced.
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.
The standard European approach for disinfectant validation consists of a basic suspension test, a quantitative suspension test (with low and high levels of organic material added to act as ‘interfering substances’) and a two-part simulated-use surface test.
A less specific measurement of effectiveness is the United States Environmental Protection Agency (EPA) classification into either high, intermediate or low levels of disinfection. “High-level disinfection kills all organisms, except high levels of bacterial spores” and is done with a chemical germicide marketed as a sterilant by the U.S. Food and Drug Administration (FDA). “Intermediate-level disinfection kills mycobacteria, most viruses, and bacteria with a chemical germicide registered as a ‘tuberculocide’ by the Environmental Protection Agency. Low-level disinfection kills some viruses and bacteria with a chemical germicide registered as a hospital disinfectant by the EPA.”
An alternative assessment is to measure the Minimum inhibitory concentrations (MICs) of disinfectants against selected (and representative) microbial species, such as through the use of microbroth dilution testing.
Guideline for Disinfection and Sterilization in Healthcare Facilities. 2008. https://www.cdc.gov/infectioncontrol/guidelines/disinfection/index.html
Microbiology (Boundless course material). Section 6.15: Chemical Antimicrobial Control. 2020. https://bio.libretexts.org/Bookshelves/Microbiology/Book%3A_Microbiology_(Boundless)
Microbiology for Beginners, Principles of sterilization and disinfection, Disinfection: Methods and Uses. 2020. https://microbeonline.com/disinfection-methods-and-uses/