Introduction:
Disinfection is a process of removal or destruction of microorganisms and reducing their number to a non harmful level.
Disinfection usually kills the vegetative form of microorganisms and doesn't affect the endospores.
The chemical which is used for disinfection of the nonliving objects (Inanimate objects) is called a “Disinfectant”.
The chemical which is used for disinfection of the living objects is called an “Antiseptic”.
Mostly the disinfectants are “Bactericidal” while some may be “Bacteriostatic”.
Ideal properties of Disinfectants:
Economical.
Easy to use.
Non toxic.
Broad Spectrum.
Compatible with surface in use.
Odourless.
Fast action.
Good solubility / miscibility.
No impact of physical factors.
Good stability.
Classification of Disinfectants:
Acids and Alkalis.
Alcohols.
Aldehydes.
Detergents and Soaps.
Dyes.
Halogens.
Heavy Metals.
Phenol and derivatives.
Quaternary Ammonium Compounds.
Acids and Alkalis:
Acids produce their germicidal action by their capability to produce H+ ions.
Some weak acids generate H+ ions enough for generating germicidal action only and not much e.g. Benzoic acid, Salicylic acid etc.
Alkalies produce their action by generating “OH- ions”.
Only weak acids and alkalis are used as disinfectant as strong acids and alkalis are corrosive in nature.
Alcohols:
They possess rapid bactericidal action.
Mechanism of Action: They act by denaturation of microbial proteins and causing dehydration.
Alcohols are also known to damage lipid blocks present in microbial cell membranes.
Ethyl Alcohol (60-70%) is the most commonly used disinfectant from this class.
Higher alcohols (Butyl Alcohol, Isopropyl Alcohol, Amyl Alcohol) are stronger in disinfectant action than ethyl alcohol.
Isopropanol is used in lower concentration that Ethanol i.e. 50-60% v/v.
Alcohols are commonly used to disinfect the skin prior to the hypodermic injections.
Alcohols above 60% concentration are found useful against viruses.
Aldehydes:
Formaldehyde and Glutaraldehyde are commonly used members from this class.
Formaldehyde is used in both gaseous as well as in liquid state.
Mechanism of Action: The mechanism of action of Formaldehyde is supposed to be forming cross linkings with amino acids present on cell membrane and protein precipitation.
Formaldehyde has a pungent odour and causes irritation to the eyes.
Glutaraldehyde is less toxic and less irritant and possesses rapid sporicidal and tuberculocidal actions.
Detergents and Soaps:
They are widely used as Surface active agents, wetting agents and as emulsifiers.
They are mainly categorized in the following categories,
Anionic Surfactants.e.g. Soaps, Sodium Lauryl Sulphate.
Cationic Surfactants.e.g. Cetrimide, Benzalkonium chloride.
Non-ionic surfactants: No antibacterial action.
Amphoteric surfactants.e.g Tego Compounds.
Cationic Surfactant are the most effective members from this class.
Mechanism of Action: They form bondings with lipid members from cell wall and result in lysis of cell.
Soaps prepared from saturated fatty acids are effective against Gram negative bacterias. While soaps prepared from unsaturated fatty acids are effective against Gram positive bacterias.
Dyes:
Basic dyes are more effective than acidic dyes.
Mechanism of Action: They act by inhibiting cellular oxidation process.
Triphenyl methane and Acridine dyes are potent members from this class.
Acridine dyes e.g. Proflavine, Aminacrine, Enflavine etc. act by demolishing DNA complexes of microbes and commonly used in treatment of burns and in ophthalmic applications and bladder irrigation.
Triphenylmethane dyes e.g Crystal violet, Brilliant green, Malachite green act by inhibiting microbial cellular oxidation process.
Halogens:
Chlorine, Fluorine, Bromine and Iodine have strong antibacterial action.
Fluorine, Bromine are well known irritants and hence not used as disinfectants.
Iodine is comparatively safer and hence used.
Chlorine is specially used for disinfection of water, its germicidal action is due to formation of Hypochlorous acid when it reacts with water.
Chlorine acts by combining with cellular proteins and bacterial enzymes making them ineffective.
Uses of Chlorine: Disinfection of water, dairy equipment, eating utensil cleaning, disinfection of open wounds, athlete’s foot.
Iodine is sporicidal, fungicidal and virucidal.
Iodine is a strong oxidizing agent and causes inactivation of microbial proteins.
Iodine is combined with surfactants like (Polyvinyl Pyrrolidone) to form compounds called “Iodophors”. Iodophors are non irritant, non staining and odorless compounds.
Heavy Metal:
Mercury, Silver and copper compounds are common members from this group.
They act by combining with microbial proteins causing denaturation.
The common compounds used are,
Mercury: Concentration (1:100 / 1:1000)
Mercuric chloride, Mercuric oxide., Metaphen.
Silver: Concentration ( 1:1000)
Silver Nitrate, Organic Colloidal Silver: Argyrol, Collargol.
Copper:
Copper Sulphate, (Fungicide, prevents algae growth in swimming pools.)
Phenol and derivatives:
Used by Lister in 1867 for first antiseptic surgery.
It is obtained by distillation of coal tar.
It has strong antimicrobial action and is used as a standard in evaluation of the efficiency of other disinfectants.
Mechanism of Action : They cause precipitation of cellular proteins and inactivation of bacterial enzymes.
Cresol becomes more potent than phenol when mixed with soap, popular brand Lysol is nothing but a cresol in a soap solution.
Quaternary Ammonium Compounds:
Most Cationic Surfactants are Quaternary Ammonium Compounds.
Mechanism of Action: Disruption of cell wall and membrane, inactivation of cellular proteins.