Disinfection is a process which aims at decreasing the amount of contaminating microorganisms. Disinfection differs from sterilization, which is a process that kills all the present microorganisms and spores. Some microorganisms or spores may survive after disinfection.
Disinfectants are any agents that have antimicrobial properties and can be used on non-living objects or surfaces to kill microorganisms; they are a key lab accessory. The use of disinfectants in the laboratory is essential as DNA, RNA, DNase and RNase from microorganisms can cause contamination and lead to erroneous and misleading results during experiments such as cell culturing, and PCR.
Several types of alcohol are known to be effective disinfectants against microorganisms, but the most commonly used alcohols in the laboratory are ethanol and isopropanol. Although alcohol can act rapidly against microorganisms (vegetative bacteria, viruses, and fungi) with a broad antimicrobial activity, it should be noted that alcohol is unable to kill many spores and some of the non-lipid viruses. Therefore, it is not recommended to use alcohol for the disinfection and sterilization of medical devices.
To achieve the highest effectiveness, the concentration of disinfectant alcohol solution should be least 70 % (v/v). Though little is known about the specific mode of action of alcohol against microorganisms, it is believed that the membrane and proteins are degraded upon exposure to alcohol, leading to cell lysis.
Hydrogen peroxide (H2O2) is another disinfectant that is widely used for decontamination. Hydrogen peroxide is an oxidant that can produce hydroxyl free radicals which can attack vital components of cells such as DNA, lipids, and proteins.
Commercially available hydrogen peroxide can be purchased in a colorless liquid form. Compared with alcohol, hydrogen peroxide shows a broader antimicrobial activity spectrum due to its action on bacterial spores. Furthermore, when compared with other disinfectants hydrogen peroxide is somewhat more environmentally friendly since it degrades contaminants to water and hydrogen, which are non-toxic to the environment.
For disinfection, hydrogen peroxide is always used at a concentration between 3 % to 6 %. However, higher concentration (10-30 %) and longer time of exposure are required for the elimination of bacterial spores. It is also worth noting that the catalase and peroxidase activities of microorganisms can affect their tolerance to hydrogen peroxide.
Chlorine is a highly active oxidizing agent that can be used as a disinfectant. Chlorine used for disinfection purposes is always sold in the form of sodium hypochlorite (household bleach, NaOCl). NaOCl always needs to be diluted to 1:10 before use. When microorganisms are exposed to chlorine or chlorine-based agents, chlorine will penetrate their outer layer and destroy the structure and activity of the cellular proteins by denaturing them resulting in microbial death.
Formaldehyde, also known as methanal, is a highly active, water-soluble chemical (Formalin) and can react with DNA, RNA, and proteins. As formaldehyde can penetrate the outer layer of spores, it is widely used for disinfection and sterilization in hospitals. Formaldehyde can also be used for preserving/fixing tissues or cells as formaldehyde is capable of forming crosslinks between proteins. Despite the high activity and efficiency of formaldehyde as a disinfectant, care should be taken due to its carcinogenic properties.