Disinfectants work to kill or damage microbes by destroying the protective layer that surrounds them.
A disinfectant is any substance intended to destroy, kill, prevent, or slow down the reproduction growth of microbes. However, disinfection doesn’t kill all microbes on a surface. Some strains may survive, even though they’re weakened by disinfectant. You may need to implement a sterilisation process if you want to totally destroy all microbes, including viruses and bacterial strains that are resistant to disinfectants.
How Do Disinfectants Work Scientifically?
Disinfectants are distinct from antimicrobial agents, such as penicillin, as well as from antiseptics like tincture of iodine. Disinfectants are meant for use on inert surfaces like floors, walls, tables, chairs, windows, and door knobs. Disinfectants like alcohols, beach solutions, and peroxides might be chemically different, but the way they work is fundamentally the same.
Disinfectants work by destroying the protective membrane or protein envelope that covers a microbe. Once this is destroyed, the internal structure and contents leak out, thereby killing the microbe or rendering it non-viable to reproduce, as in the case of viruses. Viruses technically cannot be killed because they’re not alive in the first place.
Bacterial cells are protected by a bi-layer of phospholipids. The hydrophilic heads of the cell membrane face outwards and inwards. The hydrophobic tails are sandwiched in between the outer membrane and the inner membrane.
At the centre of the hydrophilic head is phosphorus surrounded by oxygen. The mosaic arrangement of the hydrophilic head allows for the selective molecular permeability. The non-covalent bonds of the hydrophobic tails of the inner membrane are essential for maintaining the membrane structure, mainly because of Van der Waals attractive forces. Hydrophobic molecules can easily pass through the membrane through passive diffusion.
Disinfectants break the molecular bonds of the phospholipid bilayer either by oxidation reaction or through binding actions that make the membrane more permeable, such as in the case of ammonium compounds. Depending on the type and concentration of the disinfectant, as well as the type or strain of microbe, the microbe may either be killed or have its metabolic functions and growth inhibited, putting it in stasis.
Several types of disinfectants have other pathways of killing microbes. Primarily, however, disinfectants act on a microbe’s cell membrane or protein envelope. Here are the four main mechanisms by which disinfectants can disrupt the integrity of the cell membrane:
- Solubilise cell components: Non-polar molecules may dissolve, allowing the unhampered entrance of molecules from the environment, including the molecules of the disinfectant
- Interfere with the molecule transport system: Specific carrying systems can lead other molecules through the cell membrane
- Denature proteins: Membrane proteins can bind with the molecules of disinfectants, causing them to be disorganised and weak. Some proteins may become denatured
- Degrade biological functions: Disinfectants react with microbes and interfere with the normal metabolic processes
Disinfection is different from sterilisation and medical treatments using antibiotic, antiviral or antifungal medicines. Disinfection generally refers to applying disinfectants on a surface, like the surface of a table or the surface of skin that’s been wounded. Sterilisation, on the other hand, is a more extreme procedure of destroying all potentially harmful microbes on a surface or object.
Aside from using strong chemicals, sterilisation can also involve using heat and ionising radiation. On the other hand, medical treatments of infection involve using topical, oral or injectable medicines that prevent the further reproduction of the microbes inside the body. Both disinfecting and sterilising agents are potentially fatal if taken internally.
What Do Chemical Disinfectants Need to Make Them Work?
As previously mentioned, four main mechanisms exist that allow disinfectants to either destroy microbes or inhibit their growth. These mechanisms are usually aided by environmental factors, like the porosity and contour of the surface being disinfected, exposure to sunlight, and ambient temperature.
Here are some factors that can affect the effectiveness of disinfectants:
- Porosity and contour of the surface: The less porous a surface, the easier it is to disinfect. A glass window has a relatively flat surface, although there are microscopic hills and valleys on it. By being non-porous, microbes on glass surfaces are exposed, making it easy for the disinfectant to come into contact with the microbes.
- Exposure to sunlight: Microbes usually need moist environments to thrive. If the surface being disinfected is exposed to sunlight or heat, the moisture can easily evaporate. The ultraviolet rays from the sun are sufficient to kill some bacteria and fungal pores. A bedroom that has no source of natural light, for example, is relatively difficult to disinfect.
- Ambient temperature and humidity or moisture: Certain species of bacteria and fungi thrive in environments that have relatively high humidity and temperatures. Even if you apply disinfectants, microbes can make a comeback. This is one of the reasons you should regularly disinfect your bathroom.
- Concentration of disinfectant solution: Higher concentrations of disinfectants are usually very effective at killing microbes. However, you should also consider safety because high concentrations of disinfectants are hazardous to humans. For example, if you’re disinfecting swimming pools, the ideal chlorine concentration that you use should be at least 1 ppm.
How Does Alcohol Work as a Disinfectant?
Alcohols like ethyl alcohol and isopropyl alcohols are commonly used in hand sanitisers. They destroy microbes by dissolving the lipids on the viral or bacterial protective membranes. Other types of solvents like acetone work similarly, but aren’t as safe as ethyl and isopropyl alcohols.
How Does Bleach Work as a Disinfectant?
Bleach is a type of oxidizing agent that commonly has hypochlorite or chlorite as the main ingredient, similar to hydrogen peroxide. Bleach degrades or reacts with microbes, making them inactive. Strong acids and bases can also be used as a disinfectant, but they’re generally harmful to the skin and the mucus membranes. They can also corrode metal surfaces.
How Long Does Disinfectant Take to Work?
On average, a good disinfectant can kill the majority of microbes on a surface within 20 seconds. However, the efficacy of disinfectants varies. For example, hand sanitisers may only work for two minutes after application. This is especially true if a person touches a dirty object, such as a door knob.
The World Health Organization recommends washing hands for disinfection purposes for at least 40 seconds, and provides steps for washing hands using soap and water:
The speed disinfectants work at depends on several factors, such as the type of surface or substance being disinfected, the type and concentration of the disinfectant, the type of microbe, and the presence of microbes in the environment. Disinfectants are only as effective as these environmental factors.
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