The Effectiveness of Disinfectant Agents: An Overview

Disinfectants play a central role in the reduction and elimination of potential contamination in the manufacture of sensitive products such as pharmaceuticals, medical devices and cosmetics. Their effectiveness or spectrum of action depends on the active ingredients used, the type of microorganisms they are used against and the conditions of use. This article provides a brief overview of the most common active ingredients in disinfectants and their effectiveness against various microorganisms. It should also be pointed out at this point that these are generally hazardous substances and that the safety of users must always be taken into account when handling disinfectants and the relevant specifications must be observed.

1. Alcohols (ethanol, isopropanol (2-propanol), n-propanol (1-propanol), etc.)

Alcohols such as ethanol and isopropanol are widely used active ingredients in disinfectants, which are used in concentrations of 60% to 90%. They mainly work by denaturing proteins and dissolving lipids in the cell membrane of microorganisms. Alcohols are often used when rapid disinfection is required, as they are usually available as ready-to-use disinfectants and are effective against many microorganisms with a short contact time. Another aspect in favour of alcohol-based disinfectants is the problem of residues of many other active substances, particularly on surfaces with product contact or when used in the vicinity of products. Undenatured alcohol/water solutions do not leave any residues on the surface, provided they do not contain any other additives such as surfactants or wetting agents.
Effectiveness: Very effective against a wide range of bacteria, including gram-positive and gram-negative bacteria. They are also effective against many viruses, especially enveloped viruses such as influenza and coronaviruses. However, alcohol is less effective against non-enveloped viruses such as norovirus and has little to no effectiveness against bacterial spores and some fungi.

2. Chlorine compounds (sodium hypochlorite, chloramine-T,chlorine dioxide )

Chlorine compounds, especially sodium hypochlorite, are strong oxidising agents that kill microorganisms by releasing hypochlorous acid.
Efficacy: Chlorine compounds are extremely effective against a wide range of microorganisms, including bacteria, viruses (both enveloped and non-enveloped), fungi and spores. However, their effectiveness is reduced by organic matter such as blood or dirt, so the surface should be cleaned before applying chlorine compounds. They can also have a corrosive effect on metals and cause skin and respiratory tract irritation if used incorrectly.

3. Aldehydes (formaldehyde, glutardialdehyde, glyoxal, etc.)

Aldehydes act by alkylating proteins, nucleic acids and other cell components, which leads to the inactivation of microorganisms. Due to their potential to endanger human health (obstructive respiratory diseases, germ cell mutagenicity, carcinogenicity), aldehydes are no longer used in many countries, or only in certain cases.
Effectiveness: Aldehydes are highly effective against bacteria, viruses, fungi and spores. Due to their strong effectiveness, they are often used in the sterilisation of medical devices. However, they are also potentially toxic and can cause allergic reactions and respiratory problems. Their use therefore requires special precautions, including adequate ventilation and protective clothing.

4. Cationic and amphoteric compounds (quaternary ammonium compounds (QAC), e.g. benzalkonium chloride, guanidines e.g. chlorhexidine, octendin, amphoteric surfactants)

Many of these products act on the cell membrane of microorganisms. QAVs, such as benzalkonium chloride, act by disrupting the cell membranes of microorganisms, leading to a loss of cell integrity. However, QAVs, for example, tend to form a residue film on the surface when used regularly, which can lead to sticking effects.
Efficacy: They are effective against Gram-positive bacteria, some Gram-negative bacteria and enveloped viruses. However, their efficacy against non-enveloped viruses, spores and some fungi is limited. QAVs are often used in surface disinfectants and have the advantage of being less irritating and odourless. It is now also known that microorganisms may develop resistance to QAVs (based on altered membrane transporters (efflux pump) that release the active substance from the cell), which could limit their long-term use.

5. Oxidants/oxygen scavengers (ozone, hydrogen peroxide, peracids (peracetic acid))

While ozone tends to be used to treat water, peracetic acid or hydrogen peroxide are also used to disinfect surfaces and production facilities. The effect is based on the release of oxygen radicals, i.e. the products are strong oxidising agents. The oxygen radicals act on the cell membrane or cell wall or on the virus capsule. Unfortunately, the high oxidising power can also affect sensitive surfaces and lead to corrosion, for example. The decomposition of peracetic acid also produces acetic acid in addition to oxygen and water, which can lead to unpleasant odours for the user. Here too, the safety of the user must always be taken into account during use.
Effectiveness: Hydrogen peroxide is effective against bacteria, viruses, fungi and spores. It leaves no residue as it decomposes into water and oxygen and is less harmful to the environment. However, it can cause skin and eye irritation and is corrosive in high concentrations.

6. Phenols and phenolic compounds

Phenols destroy cell membranes and inactivate essential enzymes and proteins within microorganisms. In many countries, they are no longer used for ecological and health reasons or only in defined exceptional cases (disinfection of sputum, severed body parts, etc.).
Effectiveness: Phenols are effective against bacteria (especially gram-positive bacteria), fungi and some viruses. However, their effectiveness against spores is limited. Phenols are commonly used in hospitals, but their toxicity and potentially unpleasant odours have led to a reduction in their popularity.

Conclusion

The choice of disinfectant depends on the specific application, the target microorganisms (is it for production and if so which - e.g. production of viral vaccines or is it for the laboratory - if so which Bio Safety Level), and the environmental conditions (surface materials, air exchange rates (drying speed), residue requirements). While some active ingredients such as alcohols and chlorine compounds have broad efficacy, others, such as QAVs or amphoteric surfactants, are more suitable for specific applications. It is also important to follow the instructions for use and safety carefully to ensure maximum effectiveness of the disinfectant and minimise health risks. In practice, it can be useful to combine different active substances or to use them in different scenarios or to rotate them (see Annex 1 of the EU GMP guidelines) in order to achieve comprehensive disinfection and avoid adaptations or resistance formation.