Control of Microorganisms by Chemicals

Chemical Antimicrobial Agents An ideal disinfectant should have the following characteristics:

Be fast acting even in the presence of organic substances, such as those in body fluids. 2. Be effective against all types of infectious agents. 3. Easily penetrate material to be disinfected without damaging or discoloring material. 4. Be easy to prepare and stable even when exposed to light, heat or other environmental factors. 5. Be inexpensive and easy to obtain and use. 6. Not have unpleasant odor.

Conditions That Affect the Efficiency of Antimicrobial agents Population. Population Composition. Concentration and intensity of an antimicrobial agent. Duration of exposure. Temperature. Local environment.

Mechanisms of Action of Chemical 1.Reactions that affect Proteins. 2.Reactions that affect Membranes. 3.Reactions that affect other cell components. 4.Reactions that Affect Viruses.

Major Groups of Chemical Antimicrobial Agents 1.Phenol and phenolic compounds. 6. Detergents. 2. Alcohols. 7.Quarternary ammonium compounds. 3. Halogens. 8. Aldehydes. 4.Heavy metals and their compounds. 9. Gaseous agents. 5. Dyes.

1. Phenol and phenolic compounds: Practical Application: Aqueous solutions of 2 to 5% can be used to disinfect materials like sputum, urine, feces, and contaminated instruments or utensils. Derivates of phenol diluted in detergents are use din many antiseptic and disinfectant preparations. o-phenylphenol is a combination of phenol and detergent. Mode of Action: Cause disruption of cells, precipitation of cell protein, and inactivation of enzymes and leakage of aminoacids from the cells. Lethal effect is associated with physical damage to the membrane structures in the cell surface.

2. Alcohols Ethyl alcohol,CH3CH2OH, in concentration between 50 and 90% is effective against vegetative or non sporing cells. 70% concentration of alcohol is generally used. Practical Applications: Used to reduce the surface microflora of skin and for disinfection of clinical oral thermometers. Mode of Action: Alcohols denature proteins and damage lipid complexes in the cell membranes. They are also dehydrating agents.

3. Halogens: a) Iodine Traditionally it is used as tincture of iodine several preparations are: 2% iodine plus 2% sodium iodide diluted in alcohol, 7% iodine plus 5%potassium iodide in 83% alcohol and 5% iodine and 10% potassium iodide in aqueous solution. Iodophores are mixtures of iodine with surface active agents which act as carriers and solubilizers for the iodine. They are nonstaining and low irritant. Eg: Polyvinypyrrolidone (PVP-I) complex from which iodine is released slowly .

Practical Application: Used mainly as the best skin disinfectant ,used for disinfection of water ,air, (iodine vapors) and sanitization of food utensils. Mode of Action: Oxidize essential metabolic compounds such as proteins with sulfhydryl groups. The action, ay also involve the halogenation of tyrosine units of enzymes and other cellular proteins requiring tyrosine activity.

b) Chlorine and Chlorine Compounds This either in form of gas or in certain chemical combinations. The compressed gas in liquid form is used in large scale operations such as water purification plants. The convenient forms are hypochlorite- calcium hypochlorite, Ca(Ocl2) and Sodium hypochlorite, NaOCl. Practical Application: Widely used in water treatment, in food industry, for domestic use and in medicine. Products containing calcium hypochlorite are used for sanitizing dairy equipment and eating utensils in restaurants.

Solutions of Sodium hypochlorite of a 1% concentration are used for personal hygiene and as a household bleaches and disinfectants. Higher concentrations of 5 to 12% are used as house hold bleaches and disinfectants. Chorine compounds used to disinfect open wounds, to treat athlete’s foot, to treat other infections and as a general disinfectant.

Mode of Action: The antimicrobial action is due to hypochlorous acid formed when free chlorine is added to water: Cl2 + H2O HCl + HClO (hypochlorous acid) Hypochlorite and Chloramines under go hydrolysis with the formation of hypochlorous acid. The hypochlorous acid formed in each case is further decomposed: HClO  HCl + O The nascent oxygen released in this reaction is a strong oxidizing agent and through its action on cellular constituents, microorganisms are destroyed.

4. Heavy metals and their compounds Example of Compound Application Mercury Inorganic compounds: Mercuric Chloride Mercurous chloride Mercuric oxide Ammoniated mercury Bactericidal in dilutions 1:1,000;limited use due high toxicity, reduction in effectiveness in presence of organic material; insoluble compounds, used in ointments as antiseptics. Con’d

Mercury Organic compounds: Mercurochrome Metaphen Merthiolate Murcresin Less irritating and less toxic that inorganic forms; employed as antiseptics on cutaneous and mucosal surfaces; may be bactericidal or bacteriostatic. Silver Colloidal silver compounds: Silver nitrate Silver lactate Silver picrate Used as antiseptics, silver nitrate at concentration of 1:1000 dilution is bactericidal and used in few drops for the eyes of new born babies to prevent ophthalmia neonatrum and gonococcal infection. Copper Copper sulfate Most effective against algae and molds.2 ppm in water prevents algal growth, used in swimming pools and open water reservoirs; used in the form of Bordeaux mixture against fungal diseases to plants.

Mode of Action: These compound combine with cell proteins and inactivate them. Mercuric chloride act upon sulfhydryl group of enzyme.

Mode of Action: These compound combine with cell proteins and inactivate them. Mercuric chloride act upon sulfhydryl group of enzyme. 1

5. Dyes: There are two categories of dyes having antimicrobial property. They are: a) Triphenylmethane and b) Acridine Dye. a) Triphenylmethane: It included dyes like malachite green, brilliant green and crystal violet. Genrally Gram-positive organisms are easily killed by these dyes than Gram-negative ones. Crystal violet is effective at the concentrations of 1:200,000 to 1:300,000.Malachite green is effective against Staphylococcus aureus at the concentration of 1:1000, 000.

Practical Application: These dyes in low concentrations are included in certain culture media to inhibit the growth of Gram-positive bacteria. Species of Brucella bacteria can be identified based on their resistance pattern to several dyes. Mode of Action: It may interfere in cellular oxidation process.

b) Acridine Dye: There are two derivatives of acridine dye. It include: 1) Acriflavine and 2)Tryptoflavine. These have selective inhibition against Staphylococci and Gonococci bacteria. Used in treatment of burns and wounds.

6.Detergents: These are surface –tension depressants, or wetting agents used mainly for cleaning purposes. Soap is a poor detergent in hard water. Synthetic detergents used in laundry, dishwashing powders, shampoos are superior to soaps as they do not precipitate in alkaline or acid water, do not produce deposits with minerals in hard water.

Chemically detergents are classified in to: 1) anionic detergents; which ionize into anion with detergent property. Ex: Sodium lauryl Sulfate, 2) Cationic detergents; which ionize into cat ion with detergent property. Ex: Cetylpyridinium chloride ( Ceepryn), 3) Nonionic detergents which do not ionize.

Practical Application: General cleaning, laundry, household dish washers. Mode of Action: Soaps and detergents reduce surface tension of water and increase wetting property of water in which they dissolved. Soap water can emulsify and dispense oils and dirt. Microorganisms become enmeshed in the soap lather and are removed by rinse water.

7.Quaternary Ammonium Compounds: Ex: Cetrimide & Diaparene Chloride These are cationic detergents having superior antimicrobial properties. They have chemically four carbon groups (R1,R2, R3 & R4 ) linked to the nitrogen atom and R group may be any of the alkyl groups. The bactericidal power of quaternaries is extremely high for Gram –positive bacteria while they are fairly effective against Gram-negative and fungi. These have low toxicity and high solubility, stability in solution and noncorrosiveness and therefore make them ideal antimicrobial substances.

Practical Application: Used as skin disinfectants, as a preservative in ophthalmic solutions and in cosmetic preparations. Used widely in hospitals to disinfect surfaces, food processing plants and as sanitizers of utensils in restaurants. Mode of Action: These cause denaturation of proteins, interfere in glycolysis and damage to cytoplasmic membrane, alter permeability of cell structures.

8. Aldehydes These are low molecular weight compounds with general formula RCHO and have most effective antimicrobial; even sporicidal property. Two classes of compounds include a) Formaldehyde and b) Glutaraldehyde.

Formaldehyde (HCHO) Paraformaldehyde is a colorless substance which gives formaldehyde upon heating. Formaldehyde is available in a aqueous solution as formalin, which contains 37 to 40 % formaldehyde. Fumes of formaldehyde are noxious and irritating to tissues and eyes.

Practical Application: Formaldehyde in solution is useful for sterilization of instruments and in gaseous form for disinfection and sterilization of enclosed areas. Vaporization of formaldehyde into an enclosed area for adequate time at room temperature and humidity of 60 to 80 % is commonly employed for sterilizing enclosed areas. Mode of Action: Formaldehyde combines readily with proteins and nucleic acids damaging them resulting in death of organisms.

b) Glutaraldehyde: It is a saturated dialdehyde b) Glutaraldehyde: It is a saturated dialdehyde. A 2% solution this chemical agent has a wide spectrum of antimicrobial activity. It is effective against bacteria, fungi, bacterial and fungal spores and viruses,. It used for sterilizing urological instruments, lensed instruments, respiratory therapy equipment and other special equipment.

9. Gaseous agents: Sterilization by means of gaseous agents is employed for plastic syringes, blood transfusion apparatus and other laboratory materials which can not be sterilized by heat. There are two types of gaseous agents. Ethylene oxide and b)β-Propiolactone. Formaldehyde fumes are also a gaseous agent.

a) Ethylene oxide: It is a liquid at temperatures below 10 a) Ethylene oxide: It is a liquid at temperatures below 10.8°C and vaporizes quickly above this temperature. It is highly inflammable. For use, it is prepared as a nonflammable mixture of ethylene oxide and carbon dioxide or Freon. This still retains antimicrobial property. Ethylene oxide has high penetrating power. It can pass through and sterilize large packets of materials, bundles of cloth and even certain plastics. It is used in specially constructed autoclaves under specified conditions of temperature, humidity and pressure. Bacterial spores are also killed by ethylene oxide.

Practical Application: It is used for sterilizing agent for heat and moisture sensitive materials. It is used on spices, biological preparations, soil, plastics certain medical preparations and contaminated laboratory equipment. Mode of Action: The killing effect of ethylene oxide is due to alkylation with organic compounds and enzymes. Alkylation is replacement of hydrogen atom in organic compound with an alkyl group.

b) β-Propiolactone: This compound is a colorless liquid at room temperature with a high boiling point. It is considerably more active It is a vesicant and lachrymator and therefore must be handled carefully. It is sporicidal, fungicidal and virucidal. Only 2to 5mg / litre of β-Propiolactone is enough for sterilization purposes. Since it has a low penetration power and may be carcinogenic, it is of restricted use as a sterilizing agent.