Disinfection: Introduction & Classification of Disinfectants.

 

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:

1. Economical.

2. Easy to use.

3. Non toxic.

4. Broad Spectrum.

5. Compatible with surface in use.

6. Odourless.

7. Fast action.

8. Good solubility / miscibility.

9. No impact of physical factors.

10. Good stability.

Classification of Disinfectants:

1. Acids and Alkalis.

2. Alcohols.

3. Aldehydes.

4. Detergents and Soaps.

5. Dyes.

6. Halogens.

7. Heavy Metals.

8. Phenol and derivatives.

9. Quaternary Ammonium Compounds.

1. 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.

2. 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.

3. 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.

4. 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.

5. 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.

6. 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.

7. 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.)

8. 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.

9. Quaternary Ammonium Compounds:

• Most Cationic Surfactants are Quaternary Ammonium Compounds.

• Mechanism of Action: Disruption of cell wall and membrane, inactivation of cellular proteins.

They are effective against bacterias, fungi and certain protozo