Disinfectants
Chemicals that can kill vegetative bacteria, fungi, viruses & rarely bacteria spores.
Disinfection
It is a process of destruction or removal of microorganisms capable of producing an infection. We use disinfectants for such processes.
Antisepsis
It is the destruction or inhibition of microorganisms in living tissues thereby preventing the harmful effects of infection caused by them.
Antiseptic
The disinfectant that is capable of removing microbial infection from living tissue is an antiseptic.
Sanitization
It is a synonym for disinfection, particularly concerning food processing & catering. It is the process of cleaning pathogenic microorganisms from public eating utensils & objects.
Characteristics of an ideal disinfectant
- It should have a wide spectrum of activities.
- It should have fast action.
- It should be able to destroy infectious agents in clean as well as dirty conditions.
- It should dissolve easily.
- It should have high penetration power.
- It should be non-toxic & non-irritant. It should not stain tissues.
- It should not have an unpleasant odor.
- It should be easily available. It should have a long shelf life.
CHEMICAL DISINFECTANTS
The various chemical disinfectants are:
1. PHENOL & RELATED COMPOUNDS
Phenol also called carbolic acid is the first chemical agent used as an antiseptic introduced by Lord Joseph Lister (1854).
Phenol causes cell membrane damage & cell lysis.
Phenol (1%) has bactericidal action but skin & mucous membrane absorb it and cause toxicity. Thus, It is restricted and chemically related compounds like Cresol, Chloroxylenol, chlorohexidine are widely used as antiseptics.
Cresol
Cresol is a solution in soaps (Lysol). It is used for the disinfection of infected glassware. In laboratory disinfection of excreta, cleaning floors of wards & operation theatres.
Chloroxylenol
It is an active ingredient of detol.
Chlorhexidine (hibitane):
It is bactericidal at high dilution. It is an active ingredient of savlon, which is widely used in burns, wounds, pre-operative disinfection of skin, etc.
2. HALOGENS:
Chorine, iodine, bromine, and fluorine in the Free State as well as their compounds strongly act germicidal. Bromine and fluorine are irritants and are difficult to handle. Chlorine & iodine are disinfectants and strong oxidizing agents.
Iodine
It is used as a skin disinfectant and for cold sterilization of surgical sutures e.g. Weak iodine solution B.P., aqueous iodine solution BP, etc.
Iodine is also combined with surface-active agents (polyvinyl pyrrolidone) to give compounds called ‘iodophors’. These are non-irritating, non-staining, and virtually odorless.
A tincture of iodine (1-2% iodine in 70% alcohol) is used for cleaning or disinfecting skin & treating skin injuries (superficial wounds). It is virucidal, amoebicidal & active against Tubercle bacilli.
Chlorine
Chorine is available in organic, inorganic, and gaseous forms mainly employed to keep the bacterial population at low levels in municipal water. The germicidal action of chorine and its compounds is due to the formation of hypochlorous acid when free chlorine reacts with water.
Cl2+H2O HCL+HCLO
Chlorine Hypochlorous acid
Similarly, hypochlorites and chloramines undergo hydrolysis with the formation of hypochlorous acid. The hypochlorous acid is decompose into oxygen.
2HCLO 2HCL+O2
The oxygen released in this reaction is a strong oxidizing agent. It acts on the cellular constituents of microorganisms. A combination of chlorine with proteins of the cell membrane and enzymes is also responsible for the death of the microorganism.
Uses
Products containing calcium hypochlorite are used for sanitizing utensils in restaurants.
Sodium hypochlorite is used as a disinfectant for laboratory gloves, linen, syringes, and reagent bottles.
Chlorine compounds have been used to disinfect open wounds, to treat athletes’ feet and other infections.
3. ALDEHYDES
Two aldehydes are of considerable importance:
- i). Formaldehyde
- ii. Glutaraldehyde
i). Formaldehyde
- It is bactericidal, sporicidal & virucidal.
- It can be used in gaseous form or as an aqueous solution.
- The gaseous form of formaldehyde is used for disinfection of rooms & fumigation of operation theatres.
- A 10% solution of formalin (Formaldehyde gas + methanol) is used for killing bacterial cultures & suspension, cleaning contaminated surfaces, metal instruments & preservation of tissues for histopathological examination. It is also used to sterilize bacterial vaccines & in preparation of toxoids from toxins.
ii. Glutaraldehyde
- It is more effective & less irritant (toxic) than formaldehyde.
- It is active against bacteria (especially Tubercle bacilli) & their spores, fungi & then spores & various types of viruses including HIV & Enteroviruses.
- Glidex (2% buffered solution) is a commercial preparation used to sterilize cystoscopes, bronchoscopes, rubber anesthetic tubes, thermometers, polythene tubing, etc.
4. ALCOHOLS
Pure alcohol has no disinfecting properties. Three kinds of alcohols used as disinfectants are:
- Ethyl alcohol (ethanol)
- Methyl alcohol (methanol)
- Isopropyl alcohol (50-70%)
Ethyl alcohol (ethanol)
EA in concentration between 50-70% is effective against viruses.
Methyl alcohol (methanol)
Effective against fungal spores but it is toxic to the eyes.
Isopropyl alcohol (50-70%)
Better than ethyl alcohol in bactericidal property used for disinfection of clinical thermometers.
5. DYES
Two groups of dyes (aniline dyes & acridines) have been extensively used as skin & wound antiseptics. Both these groups are bacteriostatic in high dilution but have low bactericidal activity.
Aniline dyes
Includes malachite green, brilliant green & crystal violet. They are used on skin & mucous membranes as antiseptics & have been also used for some fungal infections like oral thrush.
Acridine dyes
Includes acriflavine, proflavine, aminacrine & euflavine. They are bacteriostatic & used for treating wounds & for irrigation of the bladder & vagina.
MISCELLANEOUS DISINFECTANTS
BORIC ACID
2-4% concentration used as an antiseptic for eyes & mucous membranes.
SALTS OF HEAVY METALS
Includes mercuric chloride, sodium ethyl mercurith losalicylate.
Salts of Cu, Hg, Ag, etc. are used as weak disinfectants.
Mercurochrome destroys vegetative bacteria & also fungi excluding their spores.
Merthiolate also destroys vegetative bacteria & fungi. It is a common laboratory preservative & is used in the preservation of antitoxic sera & other laboratory specimens like serum, urine, etc.
Silver nitrate 1% has been used in past for the treatment of ophthalmia neonatorum & is instilled into the eyes of a newborn after delivery.
DETERGENTS
Surface active agents or surfactants
They are used as wetting agents.
Quaternary ammonium compounds
Most of the cationic detergents are quaternary ammonium compounds. They are highly active against Gram-positive bacteria and are also quite active against Gran-negative bacteria. They are also active against fungi and certain pathogenic protozoa. Their primary mode of action is the disruption of cell walls and membranes. They also inactivate enzymes and denature proteins.
Quaternary compounds are widely used for the control of microorganisms on floors, walls, nursing homes, and other public places. They are also used as a skin antiseptic and as sanitizing agents in the dairy, egg, and fishing industries.
BETA PROPIOLACTONE
It is bactericidal, sporicidal, fungicidal & virucidal.
OXIDIZING AGENTS:
i. Hydrogen peroxide (H₂O₂)
3% solution in water is used for cleaning wounds with pus, removing pus from infected ear & may be also used as a mouth wash.
ii. Potassium permanganate
(KMnO4): Used in Seitz bath (1:1000 strength solution) in treatment of urethritis.
ETHYLENE OXIDE (ETO)
It is the most commonly used form of chemical sterilization.
ETO is a sterilant gas that has lethal effects on the proteins & DNA of bacteria & prevents their reproduction.
It is also virucidal & sporicidal.
It is highly inflammable; it is mixed with a less inert gas like CO₂ to form a non-inflammable mixture.
Due to its very good penetrating power, even through plastics, it is used for sterilization of heat-sensitive plastic goods, plastic blood transfusion or donor sets, plastic syringes, polythene tubes, Petri dishes, cystoscopes & catheterization equipment, etc.
LOWER TEMPERATURE GAS PLASMA (LTGP)
It is used as an alternative to ETO. It uses a small amount of liquid H₂02 which is energized with radiofrequency waves into gas plasma. This leads to the generation of free radicals which destroy the microorganisms.
OZONE STERILIZATION
It has been recently approved for use in the U.S. It uses oxygen, which is subjected to an intense electrical field that separates oxygen molecules into atomic oxygen, which then combines with other oxygen molecules to form ozone.
Uses:
It is used as a disinfectant for water & food.
It is used both in gas & liquid form as an antimicrobial agent in the treatment, storage & processing of foods including meat, poultry & eggs.
Many municipalities in the U.S. now use ozone technology to purify sewage & water.