Chemical Agents Used For Sterilization

As we know process of sterilization is used to remove all kind of microbial life wither living or in spore form, for any given surface. However, the process itself may differ as per the nature of surface to be sterilized and its use.

If we talk about soft tissues, or some sensitive surface over which we cannot use any physical method of disinfection or sterilization like one we used during sterilization by moist heat. From here need of chemical agents being.

Chemical agents used for sterilization or disinfection, are harsh chemicals those can kill almost all type of microbial life over the surface but still not harmful (up to certain extend) to the sot tissue over which it is applied.

There are several chemical agents those can be used as antiseptics and disinfectants. An ideal antiseptic or disinfectant should have following characters:

• Chemical agent must have a wide spectrum of activity and must be effective against all microorganism, i.e. bacteria including spores, viruses, protozoa and fungi.
• It should be active in the presence of organic matter.
• It should be effective in acidic as well in alkaline media.
• It should act speedily.
• Penetration power should be high enough to kill spores.
• It should be stable, so it can be stored for future use.
• It should not cause local irritation or sensitization.
• It should not interfere with healing.
• It should not be toxic, I absorbed in circulation by mistake.
• At last but not least, it should be cheap enough to afford and easily available, san be safe and easy to use.
Such an ideal chemical is yet to be found.

Potency of disinfectants can be identified and determined by measuring certain characters of them. Some of them are as follow:

• Concentration of the substance.
• Time taken by the agent to act on surface.
• pH of the medium.
• Temperature
• Nature of the organisms
• Presence of extraneous material

Chemical agent unlike physical agents have different mode of action on the microbial life. Some common mode of action of chemical agents can be as follow:

• Protein coagulation
• Disruption of cell membrane resulting in exposure, damage or loss of the contents.
• Removal of the free sulphydryl groups essential for the functioning of the bacterial enzymes.
• Substrate competition: a compound resembling the essential substrate of the enzyme diverts or misleads the enzymes necessary for the metabolism of the cell and causes cell death.

Here we will discuss about certain chemicals those are widely used as the disinfectants over the soft tissues.

Alcohols

Alcohols are used by mixing ethyl alcohol (ethanol) and isopropyl alcohol. It is most widely used as antiseptics over the skin and act by denaturing bacterial proteins. Alcohols solution have not reported any action on spores. To act effectively, they must be used at the concentration of 60 – 90 % in water. Protein slows its action, whereas 1% mineral acid or alkali enhances the action of alcohols. Isopropyl alcohol is preferred as it is a better fat solvent, more bactericidal and less volatile. It is used for the disinfection of clinical thermometers.

Aldehydes

Formaldehyde is widely used aldehyde for the disinfection process. It is active against the amino group in the protein molecule. In aqueous solution, it is markedly bactericidal and sporadical and also has a lethal effect on viruses. It is also used to preserve the anatomical specimens, and for destroying anthrax spores in hair and wool. 10% formalin containing 0.5% sodium tetraborate is used to sterilize clean metal instruments.

Glutaraldehyde

Glutaraldehyde have the action similar to those of aldehydes. It is specially effective against tubercle bacilli, fungi and viruses. It is less toxic and irritant to the eyes and skin than formaldehyde.

Dyes

Two groups of dyes, aniline and a riding dyes are used extensively as skin and wound antiseptics. Both type of dyes are bacteriostatic in high dilution but are of low bactericidal activity. The aniline dyes in use are brilliant green, malachite green and crystal violet. They are more active against Gram positive organisms than against Gram negative organisms. They have not reported any activity against tubercle bacilli, and hence the use of malachite green in the Lowenstein-Jensen medium. Dyes impair the DNA complexes of the organisms and thus kill or destroy the reproductive capacity of the cell.

Halogens

Halogens are used since last longer time to kill microbial life. Iodine in aqueous and alcoholic solution has been used widely as a skin disinfectant. It is one of the actively bactericidal, with moderate action against spores. It is also active against the tubercle bacteria and viruses. Compounds of iodine with no ionic wetting or surface active agents known as iodophors are claimed to be more active than the aqueous or alcoholic solutions of iodine.

Water supplies, swimming pools, food and dairy industries use chlorine for disinfection. Chlorine is used commonly as hypochlorites. Chlorine and hypochlorites are markedly bactericidal. They have a wide spectrum of action against viruses. The organic chloramines are used as antiseptics for dressing wounds.

Phenols

Lethal effect of phenols is due to its capacity to cause cell membrane damage, releasing cell contents and causing lysis. Low concentration of phenol precipitate proteins. Membrane bound oxidases and dehydrogenases are inactivated by concentrations of phenol that are rapidly bactericidal for microbes.

Phenol (carbolic acid) is a powerful microbicidal substance. This and other phenolic disinfectants derived from coal tar are widely used as disinfectants for various purposes in hospitals. Lysol and cresol are active agains a wide variety of organisms. They are not readily inactivated by the presence of organic matter and are thus good general disinfectants.

Gases

Ethylene oxide: this is a color less liquid with a boiling point of 10.7 C, and at normal temperature and pressure is a highly penetrating gas with a sweet ethereal smell. It is highly inflammable and in concentration in air greater than 3% is highly explosive. By mixing it with inert gases such as carbon dioxide or nitrogen, to a concentration of 10%, its explosive tendency is eliminated.

Its action is due to its alkylation the amino, caboxyl, hydroxyl and sulphydryl groups present in protein molecules. In addition it react with DNA and RNA. Its use as a disinfectant presents a potential toxicity to human beings, including mutagenicity and carcinogenicity. It is effective against all types of microorganisms including viruses and spores.

Formaldehyde gas: this gas is widely used for the fumigation of operation theaters and other rooms. After sealing the windows and other outlets, formaldehyde gas is generated by adding 150 g of KMnO4 to 280 ml formalin for every 1000cu. Ft of room volume. After starting generation of formaldehyde vapor, the doors should be sealed and let unopened for 48 hours.

Testing Of Disinfectants

There is no single reliable test available to determine efficiency of a disinfectant. This is due to the number of parameters which influence disinfectant activity. Traditionally in such tests phenol is taken as the standard. In the Rideal Walker test, suspension containing equal numbers o typhoid bacilli are submitted to the action of varying concentrations of phenol and of the disinfectant which sterilizes the suspension in given time, divided by the corresponding dilution of phenol is stated as the phenol coefficient (phenols = 1) of the disinfectant. This test does not represent natural concentrations as the bacteria and the disinfectant react directly without any organic matter being present.

In the Chick Martin test, the disinfectant acts in the presence of organic matter (dried yeast or feces). even this modification falls short of simulating natural conditions.

Gaurav Singh

Editor in Chief Medical Microbiology & RDT Labs - RDT Labs Magazine

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