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1 Disinfection Chemical Disinfection PAT

2 Chemical Disinfectants Phenolics Halogens Alcohols Heavy Metals Quats Aldehydes Just to name a few Antiseptics & Disinfectants Antiseptic Living tissue Disinfectant Inanimate objects Material can be both a disinfectant and antiseptic concentration PAT

3 Phenolics Phenol (carbolic acid) was first used by Lister as a disinfectant. Rarely used today because it is a skin irritant and has strong odor. Used in some throat sprays and lozenges. Acts as local anesthetic. Phenolics are chemical derivatives of phenol Cresols: Derived from coal tar (Lysol). Biphenols : Effective against gram positive staphylococci and streptococci. Used in nurseries. Excessive use in infants may cause neurological damage. Destroy plasma membranes and denature proteins. Advantages: Stable, persist for long times after applied, and remain active in the presence of organic compounds Phenolics Phenolics are active ingredients in some household disinfectants. They are also foundin some mouthwashes and in disinfectant soap and handwashes. Phenol is probably the oldest known disinfectant as it was first used by Lister, when it was called carbolic acid. It is rather corrosive to the skin and sometimes toxic to sensitive people. O phenylphenol is often used instead of Phenol, since it is somewhat less corrosive. Chloroxylenol is the principal ingredient in Dettol, a household disinfectant and antiseptic. Hexachlorophene is a phenolic that was once used as a germicidal additive to some household products but was banned due to suspected harmful effects. Thymol, derived from the herb thyme, PAT

4 Tincture of iodine Halogens: Iodine (alcohol solution) was one of firstantisepticsused used. Combines with amino acid tyrosine in proteins and denatures proteins. Stains skin and clothes, somewhat irritating. Iodophors: Compounds with iodine that are low releasing, take several minutes to act. Used as skin antiseptic in surgery. Not effective against bacterial endospores. E.g. Betadine Isodine Halogens: Chlorine When mixed in water forms hypochlorous acid: Cl 2 + H 2 O > H+ + Cl + HOCl 2 2 Used to disinfect drinking water, pools, and sewage. Chlorine is easily inactivated by organic materials. Hypochlorous acid Sodium hypochlorite (NaOCl): Is active ingredient of bleach. Chloramines: Consist of chlorine and ammonia. Less effective as germicides. PAT

5 Alcohols Kill bacteria, fungi, but not endospores or naked viruses. Act by denaturing proteins and disrupting cell membranes. Evaporate, leaving no residue. Used to mechanically wipe microbes off skin before injections or blood drawing. Not good for open wounds, because cause proteins to coagulate. Ethanol: Drinking alcohol. Optimum concentration is 70%. Isopropanol: Rubbing alcohol. Better disinfectant than ethanol. Also cheaper and less volatile Background Long recognised for disinfectant properties For disinfection in cleanroom environments only ethanol and isopropyl alcohol (IPA) are routinely used. PAT

6 Desirable properties pharmaceutical aceut ca and NHS aseptic manufacturing environments evaporate quickly leaving surfaces dry, leave very low levels of residue, have relatively low levels of toxicity, exhibit stability over time, broad spectrum of antimicrobial activity. To maximise the microbial efficiency some water is required to be present. Concentrations of alcohol in the region of 60 70% in water (v/v) have been found to be most effective. BTW Ethanol lis required dby law to be denatured dfor tax purposes and also in order to render it inedible. PAT

7 Denaturation of Alcohol This is to be achieved either by the addition of 1 part wood naphtha (largely methanol) to 19 parts ethanol (known as Industrial Methylated Spirits, or IMS), or the addition of other denaturants such as Bitrex (denatonium benzoate) at levels of about 10ppm. Antimicrobial activity Alcohols are broad spectrum disinfectants, effective against bacteria, fungi and viruses. They are also tuberculocidal. In common with many other disinfectant types, they are Sporicidal, it is believed the mode of bacterial action is by denaturation of proteins. There may also be an interference with metabolism, inhibiting the production of metabolites required for rapid cell division. In addition it has been reported that alcohols can cause cell lysis. PAT

8 Denaturation of Proteins Introduction: Denaturation of proteins involves the disruption and possible destruction of both the secondary and tertiary structures. denaturation reactions are not strong enough to break the peptide bonds, the primary structure (sequence of amino acids) remains the same after a denaturation process. Denaturation disrupts the normal alpha helix and beta sheets in a protein and uncoils it into a random shape. Denaturation occurs because the bonding interactions responsible for the secondary structure (hydrogen bonds to amides) and tertiary structure are disrupted. In tertiary structure there are four types of bonding interactions between "side chains" including: hydrogen bonding, salt bridges, disulfide bonds, and non polar hydrophobic interactions. which may be disrupted. Therefore, a variety of reagents and conditions can cause denaturation. The most common observation in the denaturation process is the precipitation or coagulation of the protein. PAT

9 Alcohol Disrupts Hydrogen Bonding: Hydrogen bonding occurs between amide groups in the secondary protein structure. Hydrogen bonding between "side chains" occurs in tertiary protein structure in a variety of amino acid combinations. All of these are disrupted by the addition of another alcohol. A 70% alcohol solution is used as a disinfectant on the skin. able to penetrate the bacterial cell wall and denature the proteins and enzymes inside of the cell. A 95% alcohol solution merely coagulates the protein on the outside of the cell wall and prevents any alcohol from entering the cell. Alcohol denatures proteins by disrupting the side chain intramolecular hydrogen bonding. New hydrogen bonds are formed instead between the new alcohol molecule and the protein side chains. Heavy metals and the Oligodynamic Effect toxic effect of metal ions on living cells, algae, moulds, spores, fungi, virus, prokaryotic and eukaryotic microorganisms, Even in relatively low concentrations. This antimicrobial effect is shown by ions of: mercury, silver, copper, iron, lead, zinc, bismuth, gold, aluminium and other metals. PAT

10 Heavy Metals (1) Include copper, selenium, mercury, silver, and zinc. Oligodynamic action: Very tiny amounts are effective. Silver: 1% silver nitrate used to protect infants against gonorrheal eye infections until recently. Mercury Organic mercury compounds like merthiolate and mercurochrome are used to disinfect skin wounds. Copper Copper sulfate is used to kill algae in pools and fish tanks. Selenium Heavy Metals (2) Kills fungi and their spores. Used for fungal infections. Also used in dandruff shampoos. Zinc Zinc chloride is used in mouthwashes. Zinc oxide is used as antifungal agent in paints. PAT

11 Heavy Metal Salts: salts are ionic they disrupt salt bridges in proteins. ti The reaction of a heavy metal salt with a protein usually leads to an insoluble metal protein salt. This reaction is used for its disinfectant properties in external applications. PAT

12 Use of Heavy metal salts AgNO 3 is/was used to prevent gonorrhoea infections in the eyes of new born infants. Silver nitrate is also used in the treatment of nose and throat infections, as well as to cauterize wounds. Mercury salts administered as Mercurochrome or Merthiolate have similar properties in preventing infections in wounds. By the way!!!! This same reaction is used in reverse in cases of acute heavy metal poisoning. In such a situation, a person may have swallowed a significant quantity of a heavy metal salt. As an antidote, a protein such as milk or egg whites may be administered to precipitate the poisonous salt. Then an emetic is given to induce vomiting so that the precipitated metal protein is discharged from the body. PAT

13 Heavy Metal Salts Disrupt Disulfide Bonds: Heavy metals may also disrupt disulfide bonds because of their high affinity and attraction for sulphur and will also lead to the denaturation of proteins. Quaternary Ammonium Compounds (Quats) Widely used surface active agents. Cationic (positively charge) g) detergents. Effective against gram positive bacteria, less effective against gramnegative bacteria. Also destroy fungi, amoebas, and enveloped viruses. Pseudomonas strains that are resistant and can grow in presence of Quats are a big concern in hospitals. Advantages: Strong antimicrobial action, colorless, odorless, tasteless, stable, and nontoxic. Diasadvantages: Form foam. Organic matter interferes with effectiveness. Neutralized by soaps and anionic detergents. E.g. Cetrimide, benzalkonium chloride PAT

14 Aldehydes (1) Include some of the most effective antimicrobials. Inactivate proteins by forming covalent crosslinks with several functional groups. Formaldehyde gas: Excellent disinfectant. Commonly used as formalin, a 37% aqueous solution. Formalin was used extensively to preserve biological specimens and inactivate viruses and bacteria in vaccines. Irritates mucous membranes, strong odour. Also used in mortuaries for embalming. Aldehydes (2) Glutaraldehyde: Less irritating and more effective than formaldehyde. One of the few chemical disinfectants that is a sterilizing agent. A 2% solution of glutaraldehyde (Cidex) is: Bactericidal, tuberculocidal, and viricidal in 10 minutes. Sporicidal in 3 to 10 hours. Commonly used to disinfect hospital instruments. Also used in mortuaries for embalming. PAT

15 Oxidising Agents (1) Oxidize cellular components of treated microbes. Disrupt membranesand and proteins. Ozone: Used along with chlorine to disinfect water. Helps neutralize unpleasant tastes and odors. More effective killing agent than chlorine, but less stable and more expensive. Highly reactive form of oxygen. Made by exposing oxygen to electricity or UV light. Leaves no residues Hydrogen Peroxide: Oxidising Agents (2) Used as an antiseptic. Not good for open wounds because quickly broken down by catalase present in human cells. Effective in disinfection of inanimate objects. Sporicidal at higher temperatures. Used by food industry and to disinfect contact lenses. Benzoyl Peroxide: Used in acne medications. PAT

16 Peracetic Acid: Oxidising Agents (3) One of the most effective liquid id sporicides id available. Sterilant : Kills bacteria and fungi in less than 5 minutes. Kills endospores and viruses within 30 minutes. Used widely in disinfection i i of food and medical instruments because it does not leave toxic residues. Efficacy of Different Chemical disinfectants The rate and extent of antimicrobial action of the chemical disinfectants are influenced by a number of factors of which the following are the more important Temperature Concentration ph Formulation and physicochemical factors Interfering substances bioload PAT

17 Temperature Rate of disinfection normally increases with temperaturet The effect of temperature increase on the rate of bacterial activity, at a fixed concentration and inoculum size is expressed quantitatively as the temperature coeficient (Q 10 ) θ ( T2 T1) t1 (Q 10 ) equation = t 2 Where T 2 and T 1 are two temperatures t that t differ by 10 o C t 1 and t 2 are the corresponding lethal times PAT

18 Concentration The rate of killl varies directly with the concentration of the disinfectant Slight concentration changes can in some cases cause dramatic changes in the killing process Dilution effects can have a crucial effect on activity it This effect is quantified by the dilution coefficient (η) Log t η η = logt2 logt1) logc1 logc2 ) Log t 2 and Log t 1 are log Log C Dilution Coefficient death times at C 2 and C 1 C 2 and C 1 are the corresponding concentrations PAT

19 ph Changes in ph may affect not only the disinfectant i t but also the growth of microbial cells ph 6 8 is optimal for many bacteria Growth rate decreases on either side of this range Formulation and Physicochemical factors (1) Correct formulation is crucial; this may affect penetrating power and thus efficacy of the disinfectant The action of the chemical disinfectants involves adsorption by the bacterial cell wall and penetration through the cell membrane into the cytoplasm and cell constituents PAT

20 Formulation and Physicochemical factors (2) Though the chemistry of the microbicide has major control over the activity, other substances can influence activity The solvent Anions and cations present Soaps Interfering Substances The influence of organic matter on the efficiency of a disinfectant is of utmost practical importance. Organic matter may Adsorb the microbicide Shield the microorganism from disinfectant activity The disinfectants themselves may chemically react with other materials present such as soaps, living tissue and anionic materials. PAT

21 Bioload (quantity) Bioload The bigger the microbial population the more severe the disinfectant conditions need to be The nature of the bioload (vegetative cells, spores etc) Spores are more difficult to eradicate Gram negative bacteria are often more difficult to kill Final Advice and Reading Lists PAT

22 Final Advice This presentation has been a brief overview of the salient principles i It is by no means a comprehensive review With this introduction you now know what s out there Go look things up!! Reading lists Russell, Hugo and Ayliffe's Principles and Practice of Disinfection, Sterilization Disinfection, Preservation and Preservation and Sterilization ti Publisher: Lippincott Williams & Wilkins, 5Rev Ed edition (1 Dec 2000) Language English ISBN-10: ISBN-13: Publisher: Blackwell Science Ltd; 4Rev Ed edition (Dec 2003) Language English ISBN-10: ISBN-13: PAT