Sterilisation by Chemical Compounds

Sterilization by using Chemical agents

Sterilization is the process of destroying removing all forms of microbial life from an object or the specimen. Thus a sterile item is one free of all living microbes

Chemicals used in following three ways for sterilization process

• Chemicals which reduce the number of microbes on inanimate surfaces that is non living surfaces for example phenol and alcohol

• Chemicals which are put on cuts and abrasion of the skin to prevent infection. for example Dettol and savlon

• Chemicals which eliminate disease causing microbes from drinking water. for example chlorine and potassium permanganate

Characteristics of an ideal antimicrobial chemical agent

• The chemical should have a broad spectrum antimicrobial activity

• It should be dissolve in water or other suitable solvents.

• It should be stable even on storage

• It should be harmless to humans or animals

• Its ingredients should not aggregate or settle to the bottom of the container.

• it should be active at ordinary temperature

• It should be able to penetrate the surface.

• it should be order less or have a pleasant smell.

• It should be readily available and inexpensive

Important chemicals used for sterilization are as follows

1. Phenol and related compounds

Phenol also called carbolic acid has the distinction of being one of the first chemical used as an antiseptic . In the mid 1800’s, the English surgeon Joseph Lister used phenol to reduce infection in surgeries . Phenol is also a standard compound with which other disinfectant are compared.

• Practical application of Phenol:

A 5 percent aqueous solution of phenol rapidly kills the vegetative cells of the microbes. However spores are much more resistant to phenol . Now-a-days ,phenol has been replaced by several chemically related compound that are less toxic to tissues and more active against microbes. These are aerosols, lizol ,hexachlorophene.

• Mode of action of phenols

Phenol and phenolic compounds damage microbial cells by altering the normal selective permeability of the cytoplasm membrane, causing leakage and vital intracellular substances

2. Alcohols

These are used very widely as skin disinfectants. Some of the alcohals used as disinfectant are as

• Ethyl alcohol

It is generally used for cold sterilization of instruments and as a disinfectant for clinical thermometers . In concentration between 70 to 90% solution of ethyl alcohol are effective against the vegetative forms of microbes . It cannot be relide upon the sterilise an object because it does not kill bacterial endospores.

• Methyl alcohol

It is not a useful as antimicrobial agent because it is less bactericidal than ethyl alcohol and is highly poisonous.

• Practical applications of alcohols

1. Alcohals wipes are the most commonly used method to clean the skin prior to draw blood sample.

2. Ethyl alcohol in concentration between 50 to 90% is effective against viruses.

3. Compare with other skin disinfectants, ethyl alcohol is the most effective in killing bacteria.

• Mode of action Of alcohol

Alcohols are known to denature the proteins and because of this they have antimicrobial activity . Alcohols are also lipid solvents ,they damage the lipid structures within microbial cell membrane. Some of their effectiveness as surface disinfectant is due to their cleansing or detergent action which helps in the mechanical removal of microbes.

3. Halogens

Halogens are strong oxidising agent and by virtue of this property they are highly reactive. They destroyed the vital compound within the microbial cell .Some of the halogens described as follows

A)... Iodine compounds

For many years tincture of iodine has been used as an antiseptic agent. Some of the methods of using it are as

• 2% iodine plus 2% sodium iodide diluted in 70% of alcohol

• Complexes of iodine with compound that act as career and solubilizing agent for iodine these substances are called Iodophores.

These are considered to be better than other iodine compounds because these are germicidal and in addition these are nonstaining and non irritating to the skin.

• Mode of action of Iodine

Iodine oxidise the metabolic compounds it combines with amino acid tyrosine, results in the inactivation of enzymes and other proteins

B)…Chlorine and chlorine compounds

Chlorine act as germicidal can be used in two forms

• As a gas

• as chemical compound

in both forms, it is one of the most widely used disinfectant. As compressed gas in the liquid form ,it is used to purify the municipal water supply and swimming pools. Inorganic chlorine compound ( hypo chloride compound which contain the chemical group -OCl ) are used as chemical compound . For example calcium hypo chloride and sodium hypo chloride.

C)…Chloramine

These are organic compound in which one or more of the hydrogen atom in ammonia is replaced by chlorine atom . Chloramines are very stable and released chlorine over a much longer time

Other uses of chlorine and its compounds

• Liquefied chlorine gas is used for the treatment of affluent for sewage treatment plants

• Products containing calcium hypo chloride are used for sanitising utensils in restaurant and equipments in dairy plants

• A solution of 1% of sodium hypo chloride is used for personal hygiene

• Mode of action

The antimicrobial action of chlorine and its compounds is due to hypochlorous acid form when free chlorine is added to water.

This acid undergoes further change giving rise to nascent oxygen

As nascent oxygen is the powerful oxidising agent so it can damage vital cellular substances

D)… Fluorine

In the form of sodiumfluoridefluoride (NaF) it is used in toothpaste for killing the germs of mouth.

4. Other heavy metals and their compounds

Heavy metals i.e metals having atomic weight higher than 40 are known to have antimicrobial property. Some of the heavy metals used as antimicrobial are mercury, lead ,antimony ,silver, copper and zinc.

Mercury and its compounds have long history of controlling infections including syphilis.

Uses of heavy metals as antimicrobial agents

• A 1 percent solution of silver nitrate was once widely used to disinfect the eyes of infants at birth to prevent gonococcal infection.

• Copper sulfate is effective as an Algaecide to kill the algae in open bodies of water. It is also a fungicide and a constituent of Bordeaux mixture- (A garden spray used to prevent fungus infection on plants).

Mode of action

Heavy metals have various mode of action one of them which is most common is the inactivation of cellular proteins

5. Detergents

Detergents are compounds that make water repellent surface more wettable. Soaps are example of detergents . Chemical detergents can be anionic ,cationic or non ionic . Most of the antimicrobial detergents belong to the cationic groups and the best example of this is quarternary ammonium cocompounds. These compounds are bactericidal and effect both gram positive and gram negative bacteria . They are characterised by

• Low toxicity

• High solubility in water

• High stability in solution

• non corrosive nature

these additional properties make the quartnery compound especially useful as an antiseptic disinfectant and sanitising agent . These are used to sterilise the followings

• Floors

• Walls

• various surfaces in hospitals

• Rooms of nursing homes and many other public places

Mode of action

These compounds act by one of the following mechanism

• denaturation of cell proteins

• interfering with metabolic process

• Damage to cytoplasm membrane