Disinfectants kill bacteria and viruses by destroying the cell membrane or protein envelope that surrounds each microbe. Exactly how they do this depends on the specific type of disinfectant that’s applied. Although disinfectants like alcohols, chlorine-based solutions and bleach are chemically different, the way they work is fundamentally the same.
Continue reading to learn more about how and why disinfectants work, as well as the different types.
In this post:
Understanding disinfectants
Disinfectants are often confused with antiseptics and other substances that are used to control infection and prevent contamination. However, there are some important differences between them.
Although both are designed to kill microbes, disinfectants are generally applied to inanimate objects such as countertops and handrails. Antiseptics, on the other hand, tend to be used on living tissue like skin or open wounds. In some cases, disinfectants like isopropyl alcohol can be used as an antiseptic too.
It’s also important to note that disinfecting isn’t the same as sterilising, which is a more extreme process that destroys all microbes on a surface (we’ll explore the differences in more detail later on).
What are disinfectants?
Disinfectants are chemical substances that are used to kill microbes that may potentially be harmful to humans. While they don’t destroy every microbe on a surface, they still play an important role in controlling and preventing infection.
Disinfectants also function as cleaning agents, although they may struggle to remove certain types of dirt like oil or rust stains.
The chemistry behind their action
All disinfectants kill microbes by destroying their external protective cover. This either means damaging the cell membrane (as is the case for bacteria) or the protein envelope (as in the case of viruses).
As we explain below, the chemical pathways may vary depending on the specific type of disinfectant.
Disinfectants in action: how do they work?
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, killing the microbe or rendering it non-viable to reproduce, as in the case of viruses.
Exactly how the disinfectant destroys the membrane or protein envelope depends on the type of disinfectant being used. It could be through one or more of the following chemical pathways:
- Cross-linking – this happens when two or more molecules form covalent bonds and join together. The process involves a molecule that contains at least two reactive ends that can attach to functional groups like primary amines and sulfhydryls.
- Coagulating – a process in which a fluid transforms into a solid or semi-solid state. For example, alcohols can cause microbial proteins to coagulate, thereby killing the microbes.
- Clumping – similar to coagulation, some disinfectants cause proteins to clump together, which then leads to the collapse of the cellular membranes.
- Structure and function disruption – cell membranes can lose their molecular structure and cohesion when disinfectant is applied. Certain disinfectants may attack the hydrophilic or hydrophobic components of the membrane. They may also affect their permeability.
- Oxidising – during an oxidation reaction, electrons are stripped from the cell membranes or protein envelope. This causes the protective cover to disintegrate.
Disinfectants are effective in killing microbes because they can destroy or disrupt the molecular integrity and functions of the cell membrane or protein envelope. Here are the four main mechanisms by which they can do this:
- Dissolving parts of the cell membrane – alcohol-based disinfectants can kill microbes in minutes by dissolving the polar parts of the phospholipids of cell membranes.
- Disrupting the molecule transport system – a microbe’s cell membrane acts like a gatekeeper, controlling which molecules are able to enter and exit the cells. Disinfectants can destroy microbes by interrupting this molecule transport system.
- Denaturing proteins – membrane proteins can bind with disinfectant molecules, causing them to be disorganised and weak. Some proteins may become denatured as a result.
- Degrading biological functions – when disinfectant molecules penetrate the cell membrane or protein envelope, they can degrade the microbe’s normal metabolic processes.
Common disinfectants
Disinfectants can be grouped into several categories including alcohols, oxidising agents, aldehydes, phenolics, and quaternary ammonium compounds. However, the most widely used varieties are alcohol and bleach-based disinfectants.
Alcohol-based disinfectants
Alcohols like ethyl alcohol and isopropyl alcohol are commonly used as disinfectants and antiseptics in hospitals and other healthcare settings. They’re also the main ingredient in hand sanitisers. These types of disinfectants kill microbes by dissolving the polar component of the cell membranes.
Rubbing alcohol (otherwise known as surgical spirit) is another widely used alcohol-based disinfectant. Available in both 40% or 70% concentrations by volume, it’s a mixture of either ethyl alcohol or isopropyl alcohol and water.
Rubbing alcohol is mainly used as an antiseptic and cleaning agent around the home. For example, it’s often used to clean newly-pierced ears, treat tick bites and disinfect hard surfaces and electronic devices.
Bleach as a disinfectant
Bleach also makes an economical and effective disinfectant. A type of oxidising agent, it commonly has hypochlorite or chlorite as the main ingredient. 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.
Sterilisation vs. disinfection: what’s the difference?
Although the terms disinfection and sterilisation are often used interchangeably, they’re actually two different processes.
Disinfection refers to the elimination or reduction of some pathogenic microbes from inanimate objects and surfaces. It usually involves the application of chemicals like bleach or alcohol-based disinfectants.
Sterilisation, however, is a more extreme process that kills all microorganisms on a surface or object. In addition to strong chemicals, high heat and radiation may be used to ensure all microorganisms are completely eliminated.
Sterilisation is essential in the healthcare sector because it prevents surgical and other medical equipment from transferring potentially dangerous microbes to patients.
Both disinfecting and sterilising agents are potentially fatal if ingested.
Conclusion
There are several different types of disinfectants, but they all follow the same basic principles when it comes to destroying microorganisms. Disinfectants work by attacking the cell membrane or protein envelope of cells and viruses. They may oxidise, dissolve, or disrupt the structure and functions of these protective coverings.
