Disinfection, sanitation, and sterilization refer to degrees of cleaning and disabling pathogens. In general, disinfection attempts to eliminate bacterial and microorganism populations by killing all harmful species. Disinfection of a surface does not destroy the spores of every microorganism, leading to eventual reappearance of those populations. Sterilization of a sample or a surface, on the other hand, kills all species; bacterial spores are also destroyed. Both disinfection and sterilization can be accomplished by chemicals (liquid or gaseous) or physical processes such as radiation and heat.
Chemicals kill bacteria and fungi through one or more of these processes:
The efficacy of chemical disinfectants depends on operating conditions, including
Phenolic compounds, hydrogen peroxide, quaternary ammonium compounds, formaldehyde, and sodium hypochlorite are commonly used disinfectants. There is no ideal disinfectant, and the best choice depends on the needs of the facility and the situation. Waste managers often find themselves balancing the antimicrobial effectiveness with the toxicity of the disinfectant solution as stronger disinfectants are often dangerous to people and animals.
Medical facilities also use antiseptic preparations on patients. These are more or less disinfectants, but the word antiseptic is used when a body part is being cleaned. The familiar alcohol swab before an injection is an antiseptic. Unlike disinfectants used to clean floors and surfaces, antiseptic preparations should act quickly and have efficacy against bacterial flora normally found on the skin. Although the term might be used by lay people, waste management professionals should not refer to liquids used to clean buildings or equipment as antiseptics. Use the word disinfectant.
Also called QACs, Quats, or quaternary ammonium cations, these chemicals have a Nitrogen atom located at the center of their molecular structures, bonded to four organic chains. The chains can be tailored in terms of length, crosslinking, and branching. Benzalkonium chloride is a well-known Quat as are alkyldimethylbenzylammonium chloride (ADBAC) and didecyldimethylammonium chloride (DDAC). Quats work by disrupting the structures of proteins and lipid membranes. Preparations are typically 200 ppm to 400 ppm active ingredient.
Quats have surfactant properties like detergents. They are usually colourless and odorless. They function as both fungicides and bactericides but are less effective against gram-negative bacteria. Anti-bacterial soaps often contain quaternary ammonium compounds and concerns about human exposure to QACs is one reason public health authorities now discourage use of these soaps.
This is the broadest category of disinfectants because so many different agents can induce oxidation of bacteria and fungi cell membranes. Oxidizing agents include
Some industrial disinfectants combine conventional oxidation agents and novel materials.
Hydrogen peroxide can be combined with nanoparticles of metals (e.g. silver and copper) to enhance its efficiency. Chlorine dioxide is used mainly in water applications (industrial water treatment, sanitation, drinking water) due to its better performance for bacteria and microorganism killing and very low by-product formation.
Silver nanoparticles are used in preservation of wood and in food packaging. Iodine is most commonly used in aqueous solutions as a wound treating agent or water additive. Electrolyzed water is an acidic solution (pH in the range 3.5-6.5) that contains hypochlorous acid and sodium hydroxide.
Ozone is a fast-acting disinfectant agent which when combined with light or heat can initiate free radical decomposition of organic compounds. Due to its high reactivity it should be applied close to the final use point of water, food, packaging or other application.
Pure alcohols and concentrated aqueous solutions of alcohols are widely used as disinfectants in health care facilities. Alcohol solutions are employed as both disinfectants and antiseptics. Ethanol (ethyl alcohol) and isopropanol (isopropyl alcohol) are the most widely used alcohols at 60 to 90 percent concentration, although other types of alcohol sometimes find their way into disinfectants. Mixtures of alcohols and formaldehydes are also used. Pure alcohols sometimes have limited diffusivity, so they work on surfaces but do not penetrate materials like slightly diluted alcohol solutions do. Alcohols are effective against lipophilic viruses, less effective against non-lipid viruses, and ineffective against bacterial spores. Because of their quick evaporation rate, application of alcohol does not always achieve sufficient contact time to be a good disinfectant.
Phenol and related compounds were among the earliest disinfectants. Popular ones include Phenol (carbolic acid, C6H5OH), Thymol (2-isopropyl-5-methylphenol, C10H14O) and Chloroxylenol (para-chloro-meta-xylenol, C8H9ClO). Hexachlorophene is often added to medicated soaps. Parachlorometaxylenol (PCMX) and dichlorometaxylenol (DCMX) are derivatives of phenol. Caution is advised when using these compounds (especially in pure forms) as some of them have shown toxicity towards humans and can be corrosive. PPE is often required when using phenolic compounds.
The Centers for Disease Control and Prevention has a webpage on chemical disinfection of healthcare facilities.
Techniques include heat application, sound treatment [6], and irradiation [7]. Physical approaches are effective against hardy microorganisms, and they often are used in combination with chemical treatment. Physical disinfection targets the mechanical, biological and chemical structure of microorganisms - not access to nutrients or the microenvironment around the pathogens. High frequency sound waves, for example, can break down the cell walls of microorganisms. Their greatest advantage over chemical disinfection is that they can function in all chemical environments.
Carbon allotropes have been a field of active research for the development of novel disinfectant agents. Allotropes include graphene, graphene oxides and functionalized forms of graphene. Research has shown that graphene oxides are extremely effective towards gram negative and moderately effective towards gram positive species [4, 5]. Advantages of these materials are their hardiness and resistance to degradation. Their porosity can be modified when the particles are synthesized, adding other parameters.
One way to establish if a material or process is an effective disinfectant is if it passes the AOAC Use Dilution Test https://www.epa.gov/pesticide-analytical-methods/use-dilution-method-performance-standard-revision-document. This test dates back to the 1950s. It tests the efficacy of a disinfectant solution or liquid under certain conditions: a piece of stainless steel is exposed to bacteria and then immersed in the purported disinfectant. The EPA has more.
Most microorganisms exhibit tolerance towards some types of disinfectants. In other words, chemicals that disable some microorganisms will not work on others. Broad spectrum disinfectants are effective against many bacteria and viruses. Narrow, or limited-spectrum disinfectants kill a more limited range of pathogens. Iodine and iodophors are narrow spectrum, which is one reason they are little used any more. Glutaraldehyde and Quats are broad spectrum.
Disinfectant types can be classified according to their effects which are described as follows:
These disinfectants destroy or kill vegetative bacteria along with medium-sized lipids containing viruses and few fungi excluding (M.tuberculosis) in less than 10 minutes. These disinfectants are not effective for small non-lipid viruses, mycobacteria and fungi. Low-level disinfectants include quaternary ammonium compounds, phenolics, and concentrated alcohol.
Examples include a combination of quats and alcohol (effective on pathogens such as norovirus and mycobacteria), bleach, and mixtures of bleach and peroxide. Bleach disinfectant is frequently used to clean clothing worn in a medical setting and it is effective against viruses, some bacterial spores and mycobacteria. Bleach and hydrogen peroxide mixtures are more effective against complex bacterial spores than bleach alone.
The active ingredient in bleach is NaClO (sodium hypochlorite). The concentration of NaClO is important in formulation of liquid disinfectants. Sodium hypochlorite kills bacteria, viruses and fungi by denaturing the protein in disease-causing microorganisms.
Germicides are formulated to destroy or inactivate all microbial pathogens excluding plenty of bacterial endospores are high-level disinfectants. Active ingredients which are found commonly in high-level disinfectants are hypochlorite, glutaraldehyde, hypochlorous acid, hydrogen peroxide and ortho-phthalaldehyde. These are mostly used at the terminal step during the cleaning/processing of critical devices and semi-critical devices in medical facilities, including dialysis units. These liquids are not used to clean floors or walls.
High-level disinfectants are effective within 20 minutes. They are often combinations of two chemical compounds. A combination of peracetic acid and hydrogen peroxide is often used. A blend of bleach and hydrogen peroxide is another formulation. Other commercially available disinfectants are a 0.8% peracetic acid + 1.0% hydrogen peroxide combination and 0.23% peracetic acid + 7.35% hydrogen peroxide.
The FDA gives guidance on which commercial preparations can be used as high-level disinfectants. Often, the same material can be used as a sterilant if the contact time is higher. The FDA has a webpage here.
The waste manager or industrial hygienist gets paid to make these decisions in each specific context.. There is no answer from a textbook or website. The best disinfectant should be chosen from commercially available options. Don’t try to create your own disinfectant unless you have a thorough knowledge of chemistry. Selection factors include:
Never combine two disinfectants or two cleaning solutions. Use them sequentially if needed, with a rinse of the floor or equipment in between applications.
If you clean with detergent prior to disinfection, it is likely the disinfection will be more effective. Some preparations combine detergents with disinfectants, and there is nothing per se wrong with that. But cleaning in more than one stage is both theoretically superior and in real life shows better results than single-stage washing.
Although there is no standard industry practice here, managers should consider changing disinfectants used for a given application occasionally. This reduces the chances of pathogens developing resistance. Commercial preparations tend to be unique - no two companies make the exact same formulation - but the active ingredients are often the same.
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