Essay on Antiseptics and Disinfectants | Animals | Pharmacology

This article provides a note on the antiseptics and disinfectants.

History:

Use of antiseptics and disinfectants evolved from the ancient Egyptian process of embalming. The Egyptian and other ancient people used various concoctions such as volatile oil, wines, vinegars, honey, balsam etc. as embalming. Persian required water to be stored in bright copper vessels. Salting, smoking and spicing the foods are beyond recorded history.

Chlorine was used in a Viennese hospital by Ignaz Semmelweis, a Hungarian Obstetrician, in a practical demonstration of the beneficial action of antiseptics (1847-49). A few years later, Joseph Lister recognized the significance of observation of Semmelweis, Pasteur and others, applies them to surgical techniques with the objective of antiseptics and disinfection.

In 1865, Lister announced the methods of sterilization of bandages, surgical dressings and surgical instruments and of the antiseptics of wounds. To achieve asepsis, he used carbolic acid and observed general principle of cleanliness.

During the epidemics of Rinderpest raged in early 18th century, the authorities of affected countries recommended for disinfecting contaminated premises and materials with concentrated soda.

Definition:

Antiseptics and disinfectants are non-selective, anti-ineffective agents which are applied topically. Their activity ranges from simply reducing the number of micro­organisms to within safe limits of public health interpretations and to destroying all microbes (Sterilization) on applied surface.

In general, antiseptics are applied on living tissues to suppress or prevent microbial infections. Whereas disinfectants are germicidal compounds usually applied to inanimate surfaces. Many undiluted antiseptic act as disinfectants and vice-versa. The terms disinfectant and antiseptic are commonly used interchangeably.

Ideal Properties of a Disinfectant:

It should be fast acting, bear broad spectrum activity against microbes, non- staining, non-corrosive, deodorizing, odorless, posses detergent properties, residual action after rinsing, least toxic, stable during storage, be simple and economical to use.

It should control all microbial growth, harmless to humans, animals and objects, as well as should neither be inactivated by protein, organic material, pus, blood nor allow the emergence of resistant populations.

Mode of Action:

Mode of action basically fall into in two groups:

I. Compounds exert their antimicrobial effect by alteration of cellular membranes (i.e. either on cell wall, or cell membrane). Cell wall (maintains integrity of cell) disruption by disinfectants, producing cell bursting due to osmotic effects.

Cytoplasmic membrane contains cytoplasm and controls passage of chemicals into and out of cell, when damaged, cellular contents leak out. Viral envelope responsible for attachment of virus to target cell, and its damage leads to interrupt viral replication.

II. Compounds exert their antimicrobial effect by interference with protein and nucleic acid synthesis. Protein function depends on its 3-D shape and extreme heat or certain chemicals denature proteins. Chemicals, radiation, and heat alter or destroy nucleic acids which produce fatal mutants and halt protein synthesis through action on RNA.

Resistance Development:

Strains resistant to antimicrobial agents are likely to develop wherever cleaning with disinfectants is routine such as in Hospitals, Pharmaceuticals plants, Animal rearing units, Food processing plants etc.

The mechanism of resistance development with disinfectant is not well established but thought to be either:

(a) Cells possess or can accumulate increased amount of lipid in or around the cell wall which impede the uptake of antimicrobial agent.

(b) Some microbial strains developed or possess the ability to degrade the antibacterial agent and render it harmless,

(c) Because of inherent structural features of some bacteria, possess an intrinsic resistance.

Terminology of Microbial Control:

The terminology used to describe disinfecting agents can be confusing because in addition to scientific terms used to describe disinfectants many vague terms are frequently used by the general public. Unlike many antimicrobials, disinfectants are usually micro-cidal rather than static. Because inanimate do not have immune system to help in combating infection.

(a) Antiseptics are applied on tissues to suppress or prevent microbial infections.

(b) Disinfectants are germicidal compounds usually applied to inanimate surfaces/ objects (surgical equipment, floors, tabletops). Many undiluted antiseptic act as disinfectants and vice-versa. Antiseptics and disinfectants may also be described as sanitizers or sterilizers.

(c) Sanitizers are chemicals that reduce the number of micro-organisms to a “safe” level, without completely eliminating all microorganisms.

(d) Sterilizers are chemicals or other agents that completely destroy all microbes on applied surface.

(e) Germicides preferably used for household products and is non-specific term that include any chemical agent that kills microorganisms (bacteria, viruses, protozoa & fungus). Bactericidal chemicals kill bacteria, virucidal chemicals kill viruses, fungicidal chemicals kill fungi, protozocidal chemicals kill protozoa, and sporicidal chemicals kill microbial spores.

Classification of Disinfectants:

A. Physical Agents:

Include exposure to extremes of heat, exposure to extremes of cold, desiccation, filtration, osmotic pressure, and radiation (light). Heat sterilization is an efficient and convenient procedure. Moist heat (boiling, autoclaving, pasteurization, ultrahigh-temperature sterilization) penetrates clumps of organic matter and reaches surfaces not readily available to chemical disinfectants.

Moist heat produces germicidal effect by protein coagulation. Dry heat requires higher temperatures, and longer exposure than moist heat. Ultra violet light has anti microbial activity. Physical agents are also known as Natural disinfectants (sunlight, heat, cold, desiccation and agitation).

B. Chemical Agents:

(i) Acids and alkalies

(ii) Alcohol

(iii) Biguanides

(iv) Oxidizing agents

(v) Heavy metals

(vi) Phenols and related compounds

(vii) Reducing agents

(viii) Surface acting compounds/detergents

(ix) Dyes

(x) Vapour phase disinfectants

(i) Acids and Alkalies:

Acids produce action by its hydrogen ion, bacteriostatic at pH approx. 3 to 6 and bactericidal at pH less than 3. Strong mineral acid (HCl, H₂SO₄) at concentrations of 0.1-1 N used as disinfectants but their corrosive action limits their usefulness.

Acids are used as food preservative (Benzoic acid), antiseptics (Boric acid, acetic acid), fungicides (Salicylic acid, Benzoic acid) and as cauterizing agents (strong mineral acids). Sulphuric acid and mixture of acids with anionic detergents are used as effective sterilizers of equipment.

Alkalies produce action by its Hydroxyl ions and exert antimicrobial activity. At pH more than 9 inhibit most bacteria and many viruses. Sodium Hydroxide and Calcium Hydroxide used as disinfectants. Quick lime (CaO) soaked in water produces Calcium hydroxide or aqueous suspensions used to disinfectant premises. A 4% solution of sodium carbonate is employed in the cleansing and disinfection procedures.

(ii) Alcohols:

Its antimicrobial effect is related to their lipid solubility (damages bacterial membrane) and ability to precipitate protoplasmic proteins. However, do not destroy bacterial spores. Ethyl alcohol (Ethanol) and Isopropyl alcohol (Isopropanol) are most widely used alcohols, used in concentrations ranging from 30-90% in aqueous solutions.

70% Ethanol or 50% Isopropanol usually gives best results. Rubbing Alcohol is a mixture of alcohols with Isopropanol as its principal ingredient, used as skin disinfectants and rubefacient. Ethyl alcohol (70%) used as ritual pre-injection skin swab.

(iii) Biguanides:

The most popular antiseptic of this group is Chlorhexidine which has potent antimicrobial activity against gram positive and some gram negative bacteria but not against spores. Chlorhexidine in susceptible organisms disrupts the cytoplasmic membrane or by disruption of bacterial cell wall.

Chlorhexidine activity is well maintained in presence of tissue fluids and pus and also in presence of other antiseptics. However, Chlorhexidine is incompatible with anionic compounds including soap. It is one of the most commonly used surgical and dental antiseptics.

At 4% emulsion of Chlorhexidine gluconate used as skin cleanser, 0.5% w/v in 70% Isopropanol used as general antiseptic and 0.5% w/v in 70% Isopropanol with emollients as hand rinse. Chlorhexidine is also incorporated in shampoos, ointments, skin and wound cleansers, teat dips, surgical scrubs for its antimicrobial properties.

(iv) Oxidizing Agents are of two types:

(a) Those release oxygen, e.g. Peroxides (H₂O₂, Sodium perborate, Benzyol peroxide etc.) exerts mechanical cleansing action resulting from rapid oxygen release and antiseptic and deodorant action through their strong oxidizing effect of nascent oxygen produced in contact with tissue. Nascent Oxygen becomes inactive when combines with organic matter. Peroxides have little or no action against spores.

H₂O₂ liberates oxygen when in contact with catalase present on wound surfaces and mucous membranes. H₂O₂ solution is used in purulent pocketing wounds. Mechanical action resulting from the rapid release of oxygen helps to remove pus and cellular debris from the wounds and is valuable for cleaning and deodorizing infected tissue.

(b) Those cause oxidation without oxygen release, are Halogens (iodine, chlorine, and iodophores etc.) and Potassium permanganate. Potassium permanganate solution 1: 10,000 kills many microorganisms in one hour. Its higher concentration irritates the tissues. Old solutions or when come in contact with tissue, solution turn chocolate brown or brown in color and rapidly lose their antiseptic activity.

Potassium permanganate stains the tissues and clothing brown. Potassium permanganate solution (5%) has astringent action and used as footbath to harden greyhound’s feet and also to reduce excessive granulation. KMnO₄ solution (1: 1000) used as wound for antiseptics and deodorant purposes.

Halogens such as Iodine and chlorine produce their activity due to high affinity for protoplasm and are believed to oxidize proteins and interfere with vital metabolic reactions. Elemental Iodine is a potent germicide with a wide spectrum of activity and low toxicity to tissues. Iodine is poorly soluble in water but readily dissolves in ethanol and enhances its antibacterial activity.

Commonly used Iodine preparations are weak Iodine solution or weak tincture, Strong Iodine solution or strong tincture of Iodine or liniment of Iodine, Aqueous solution of Iodine/Lugol’s Iodine used for intrauterine and vaginal irrigation to strength of 0.2%.

Chlorine is a strong oxidizing agent and extremely toxic and exerts potent germicidal effect against viruses, protozoa and fungi through its hypochlorite (OCI) which releases oxygen slowly when exposed to atmosphere or organic material.

Chlorine at Alkaline pH ionizes chlorine and decreases its activity by reducing its penetrability and widely used to disinfect water supplies, inanimate objects such as utensils, bottles, and pipelines. Chlorinated lime (Bleaching powder) a mixture of CaCl2 and Ca-OCl (hypochlorite) yield 30% chlorine and used as disinfection of water supply, livestock premises, destruction and disposal of carcasses etc.

Iodophores consist of iodine and a neutral carrier polyvinyl pyrolidone (povidone) are water soluble combinations. They slowly release iodine as antimicrobial agents and widely used as skin disinfectants, particularly before surgery. They do not sting or stain and are non toxic to tissues but corrosive to metals.

They are effective against bacteria, viruses and fungi but less against spores. Iodophores solutions retain activity at pH less than 4, even in the presence of organic matter and often change colour when activity lost. Iodophores used in teat dips to control mastitis, dairy sanitizers and as a general antiseptic or disinfectant for various dermal and mucosal infections.

(v) Heavy Metals:

Inorganic mercurials (mercury chloride), early antiseptics replaced by less irritant and less toxic organic mercurials (merbromin, thimerosal, nitromerosal, phenylmercuric nitrate) act by inhibiting the bacterial enzymes through their affinity for sulphydryl groups. Mercurials are not effective against spores and due to persistent of mercury in environment, less in use.

Silver compounds are also in use but have caustic effect and 0.5% silver solution applied as a burns dressing to reduce infection. Silver ions combines with sulfhydryl, amino, phosphate and carboxyl groups and thus precipitate proteins and also interfere with essential metabolic activities of microbial cells.

(vi) Phenols and related compounds (Phenolics, Cresols):

Phenol (Carbolic acid) is a first disinfectant, has historic interest used as antiseptic by Joseph Lister in 1867. All Phenols denatured the proteins and are general protoplasmic poisons. At 1-2% concentrations, it is bactericidal/fungicidal. Phenol has good penetrating power into organic matter and is mainly used for disinfection of inorganic equipment and organic materials.

Phenol is also incorporated in cutaneous applications for pruritus, stings, bites, burns, etc. because of its local anesthetic and antibacterial properties to relieve itching and control infections.

Phenol is used to cauterize infected areas e.g. infected umbilicus of neonates. Phenol is still included as standard by which other disinfectants are to be judged. But because of its irritant and corrosive properties and potential systemic toxicity, phenol is not much in use as an antiseptic.

Cresol (Cresylic acid or Methyl phenol) a 2% solution of either pure Cresol or saponated cresol “Lysol” in hot water is commonly used as a disinfectant for inanimate objects. Lysol in preferred than cresol because of its greater water solubility. Cresol is very effective against acid fast bacteria, less effective against viruses and has no effect on spores.

Phenols and Cresols are especially toxic to cats and dogs and cause death due to respiratory or cardiac failure but cresol toxicity is lower. Hence, newer derivatives of phenol and cresol such as various chlorinated cresols and the phenyl-mercuric compounds are now more commonly used for antiseptic purposes.

Hexachlorophene is widely used in medicated soaps. Repeated exposure of skin to high concentrations of hexachlorophene may lead to sufficient absorption of antiseptics to cause spongiform degeneration of the white matter in brain and resultant nervous disorders (neurotoxicity):

Pine Tar is primarily used for antiseptic bandaging of wounds of the hoof and horn. Pine Tar contains phenol derivatives that provided antimicrobial properties. Resorcinol is Keratolytic and anti-pruritis, employed on seborrheic dermatitis, acne, ringworm and eczema as 6% lotion or ointment. Where as hexyl-resorcinol used as mouth wash, lozenge and antifungal.

Chloroxylenols (PCMX, DCMX) are the compounds which outdate phenol and cresol as antiseptics. Parachlorometaxylenol (PCMX) and Dichlorometaxylenol (DCMX) are broad spectrum bactericides with greater activity against gram +ve bacteria, active in alkaline pH, diminishes its activity in contact with organic matter.

(vii) Reducing Agents:

Formaldehyde and Gluteraldehyde are readily soluble in water. Their solutions are irritant or caustic to tissues, potent germicidal and also against spores. Gluteraldehyde is less irritant to skin and mucous membrane than formaldehyde. They do not lose appreciable antimicrobial properties in presence of organic matter and are non-corrosive to metals, paints and fabric.

Both used as disinfectant, Formaldehyde is a gas where as Glutaraldehyde is oil at room temperature. Formaldehyde is externally used as fumigant disinfectant or as an aqueous disinfectant spray, but vermin are not be killed. For building fumigation mix KMn0₄ and formaldehyde solution in a ratio of 3: 5, using 45 to 90 g KMnO₄ for each 3m³ and room should be closed for at least 10 hr.

Vermin are not killed by formaldehyde fumigation, but fabrics and dyes are unaffected. Glutaraldehyde, a 1-2% alkaline solution (pH 7.5-8.5) in 70% isopropanol is a more potent germicide than 4% HCHO, used to sterilize surgical and endoscopic instruments, plastic and rubber apparatus and for treatment of blood products to inactivate viruses.

Formalin contains 40% HCHO gas in aqueous solution with variable amounts of methyl alcohol to prevent polymerization. Similar to potassium permanganate, formalin should be applied diluted 1: 10 to give 4% formaldehyde solution for hardening greyhounds’ feet, 1-10% solution of HCHO commonly used as disinfectant.

Sulphur dioxide as Gaseous fumigant is produced by burning Sulphur in closed spaces. Sulphur burnt by sulphur candles or sulphur mixed with 1/40 of its weight of charcoal to help in burning. SO₂ is still occasionally used as fumigant disinfectant for animal houses to destroy bacteria and viruses, parasites and vermin.

For maximum effect, their surface should be moist as the SO₂ gas dissolve in water to form sulfurous acid (bactericidal). However, the reducing effect of the acid also corrodes metals, rot fabrics and bleach dyes and considered as disadvantage. As Sodium metabisulphite SO₂ is used as a preservative for foods, and preservative antioxidant for adrenaline or procaine in strength of 0.1 to 0.2%.

(viii) Surface acting compounds/detergents:

Detergents groups collectively referred to as surface-active agents, are classified as emulsifying and cleansing agents frequently posses antibacterial properties. Detergents have properties of reducing surface tension (emulsifying agents), wetting, spreading penetrating, foaming and some cases antifoaming, and cleansing. Detergents antibacterial activity is greatly reduced by organic matter such as blood, serum and pus.

Surface acting agents are of mainly two types:

A. Ionic detergents are of two types, Anionic detergents (Active in mildly acidic solution by virtue of active anions) and Cationic detergents (Active in alkaline solution is vested in the cation). Anionic detergents used in Veterinary field are the Soaps (Na or K Oleates), Ca and ammonium mandelates and Na lauryl sulphate and having antibacterial and cleansing action.

Soaps are also combined with stronger antibacterial agents (Phenolics or chlorhexidine). Hard soap used as a lubricant enema or rectal suppository in the treatment of faecal impaction. Ionic detergents have little or no effect on viruses, spores or fungi where as Cationic detergents sometimes referred as ‘reversed soaps’ such as Quarternary ammonium compound (i.e. Cetrimide, Benzalkonium chloride solution) and the rosaniline and acridine dyes.

Cationic detergents as a groups agents are active against gram +ve and gram – ve bacteria. All anionic detergents are antagonized by cationic compounds and vice-versa.

B. Non-ionic or amphoteric detergents or Ampholytic surfactant biocides which do not ionize. Ampholytes are amphoteric surfactants possess at least one anionic and one cationic group and have anionic, non-anionic or cationic properties depending on pH.

(ix) Dyes:

Acridine derivatives such as Acriflavine, Euflavine (neutral acriflavine), Aminocrine HCl, and Proflavine hemisulphate. Acridine derivatives dye mainly active against pyogenic organisms, particularly streptococci and Staphylococci. Acriflavine is mixture of acridine derivatives and is acid in solution. Euflavine (neutral acrifavine) is mixture of chlorides precipitated by addition of NaCl to a neutral solution of acriflavine.

Flurescein dyes such as Fluorescein sodium, used in small animals as a diagnostic aid. For any corneal ulcerations detection light green fluorescent body and foreign bodies show up as dark area within the fluorescent zone.

(x) Vapour-phase Disinfectants or Gaseous Disinfectants:

Alkylating agents such as formaldehyde, ethylene oxide, and propylene oxide are active against bacteria, viruses, and spores. Ethylene and propylene oxide are gaseous fumigants used for sterilizing animal feed, human food, surgical equipment that can not be autoclaved, laboratory equipment, etc.

Activity Evaluation of Antibiotics:

Laboratory testing of disinfectants have been devised for assessing the efficiency of disinfectants. For the testing, the efficacy of phenolic-type disinfectants a pure phenol solution has been taken initially as standard known as “the phenol coefficient”. This phenol coefficient expressed as the Rideal-Walker coefficient or Chick-Martin coefficient depending on test used.

The Rideal-Walker test compared the performance of a disinfectant with the phenol and the results were calculated as a phenol coefficient, given as a number following the letters RW. Higher number indicates better disinfectant performances. After Rideal-Walker test, Chick and Martin published their phenol coefficient test method.

Rideal-Walker test and Chick and Martin coefficients are similar in design but Chick and Martin coefficient test is done in the presence of organic matter such as yeast and simulates the organic matter which will contact the antiseptic in-vivo during its use as an antiseptic. Both the test is carried out in vitro.

Introduction of Non-phenolic types of disinfectants show different properties and vary greatly and also are unsuitable for RW or CM test. Other tests include AOAC (The German Society for Hygiene and Microbiology), DGHM (The Dutch Phytopharmacy Commission) and Kelsey-Sykey test.

Conditions to Use:

Disinfectants play a key role in maintaining the health of animal, whether they are on a farm, in a hospital, clinics, in a research facility, or in breeding colonies, and also serve as sanitizing agents in food producing establishments. Topical anti-infective agents are extensively used in surgery for antisepsis of the surgical area and surgeon’s hands and to disinfect surgical instruments, apparel, and hospital premises.

Other common uses are as disinfectants for home and farm premises, in water treatment, in public health sanitation and as antiseptics in soaps, teat dips, and dairy sanitizer. Antiseptics are also used for treating local infections.