Pathogenic microorganisms. The reasons for the large variety of disinfectants.
The use of disinfectants to substantially reduce the number of pathogenic microorganisms can take very different forms depending on the location and requirements. It may involve treating smooth surfaces (floors, walls, equipment, containers, etc.), instruments, air, water, the hands, porous surfaces, coolants and clothing.
The organisms targeted by disinfectants fall into a number of categories: bacteria, fungi (mycoses and yeasts), mycobacteria (the pathogens that cause tuberculosis), viruses and bacterial spores.
Other microorganisms such as protozoa and algae are not among the organisms targeted by disinfectants.
Characteristics of disinfectants
The ability of microorganisms to protect themselves from outside factors and ward off the defences of the infected organism explain why there is no such thing as a universal disinfectant. One active substance might work well against bacteria but be less good or poor when it comes to viruses and fungi. Finding out a product’s range of effects involves testing it on all types of microorganism.
The protective mechanisms also explain why the addition of a few per cent of a simple additive is enough to make a disinfectant more or less effective. A typical example is the disinfectant property of alcohols (1-propanol, iso-propanol and ethanol). Mixed with between 10% and 30% water, alcohols are a good disinfectant. The water enables the alcohol to penetrate the cell wall into the bacteria, causing precipitation of proteins and ultimately destroying the bacteria. Pure (100%) alcohol isn’t effective because it causes precipitation of external proteins, preventing it from penetrating further into the cell. Another example is the addition of very low concentrations of quarternary ammonium to a solution. This improves the distribution of the product on the surface and boosts its efficacy.
The pathogens that cause tuberculosis (Mycobacterium tuberculosis) are among the most resistant bacteria. This bacterium, which is particularly significant in hospitals, has a waxy coating on its cell surface that makes it especially resistant to disinfectants. Other bacteria, so-called gram-negative bacteria, are also resistant to disinfectants because in addition to the peptidoglycan layer all bacteria possess, they also have an outer layer of proteins and lipopolysaccharides.
There are viruses that are surrounded by a lipid layer (influenza and hepatitis C), and others without an outer lipid envelope (adenoviruses and papovaviruses). Paradoxically, this lipid layer can be easily destroyed with chemicals, which makes viruses with a viral envelope vulnerable. Viruses without an envelope, however, are “used” to having to resist the external environment and are therefore more resistant to disinfectants. Generally speaking a disinfectant that is effective against viruses without an envelope, such as the polio virus, is also seen as being effective against viruses such as HIV/AIDS that are less resistant. Other viruses such as hepatitis A are very resistant and more difficult to test.
For each group of microorganisms the efficacy is tested for specific types, which serve as models for the group in question. The efficacy for each of these groups has to be demonstrated separately. Only pathogens or groups of pathogens that have been tested and the product is actually effective against can be specified on the label and in the directions and advertising.
Last modification 28.02.2017