Chemical Methods Of Disinfection

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Chemical Methods Of Disinfection

  1. 1. Chemical Methods ofChemical Methods of DisinfectionDisinfection Fe A. Bartolome, MD, FPASMAP Department of Microbiology Our Lady of Fatima University
  2. 2. SterilizationSterilization • Killing of all microorganisms, including bacterial spores DisinfectionDisinfection • Reducing the number of bacteriaReducing the number of bacteria to a level low enough that diseaseto a level low enough that disease is unlikely to occuris unlikely to occur • Some organisms and bacterialSome organisms and bacterial spores may survivespores may survive
  3. 3. AntisepticsAntiseptics • Chemicals used to kill micro- organisms on the surface of skin and mucous membranes
  4. 4. • Differ from systemically-active anti- microbials in that they possess little selective toxicity  toxic not only for microbial pathogens but for host cells as well • Can be used only to inactivate microorganisms in the inanimate environment or, to a limited extent, on skin surfaces  cannot be administered systemically
  5. 5. Factors that affect efficacy of a chemical agent:Factors that affect efficacy of a chemical agent: 1. Concentration of chemical agent • Higher concentration bactericidal EXCEPT alcohol (50% - 80%) 2. Time • Longer time of exposure, better killing action 3. Temperature • High temperature speeds up rate of chemical reaction 4. Nature of surrounding medium • pH of medium; presence of extraneous materials like pus or blood 5. Nature of the organism • Ability to produce spores; number & size of inoculum
  6. 6. Characteristics of a good chemical disinfectant orCharacteristics of a good chemical disinfectant or antiseptic:antiseptic: 1. Able to destroy a wide variety of microorganisms 2. Fast-acting  short contact time 3. Not affected by the presence of other substances such as organic matter 4. Non-toxic to human tissues as well as non- corrosive and non-destructive to materials for which it is used 5. Should leave a residual antimicrobial film on the treated surface 6. Water-soluble and easy to apply 7. Inexpensive and easy to prepare 8. Stable under storage and shipping conditions 9. Odorless
  7. 7. Damage Cell MembraneDamage Cell Membrane A.A.Surface active agents – interact with theSurface active agents – interact with the lipid in the cell membranelipid in the cell membrane  disrupt celldisrupt cell membranemembrane 1. Cationic agents • Quarternary ammonium compounds • Cationic detergents widely used for skin antisepsis • Effective at alkaline pH • Example: zephiran, benzalkonium chloride
  8. 8. Damage Cell MembraneDamage Cell Membrane A.A.Surface active agentsSurface active agents 2. Anionic agents • Remove dirt through the process of emulsification • Effective at acidic pH • Example: soaps and detergents  Composed of long-chain, lipid- soluble, hydrophobic portion and a polar hydrophilic portion
  9. 9. Damage Cell MembraneDamage Cell Membrane B.B.Phenolic compounds – also denature proteinsPhenolic compounds – also denature proteins 1. Phenol • No longer used due to toxicity • Mainly used as gold standard in the evaluation of new chemical agents using the phenol coefficient test  Ratio of the concentration of phenol to the concentration of the agent required to cause the same amount of killing under standard conditions of the test
  10. 10. Damage Cell MembraneDamage Cell Membrane B.B.Phenolic compoundsPhenolic compounds 2. Cresols (Methylphenol) • Phenol derivatives • More potent and safer • Example: lysol 3. Hexachlorophene • Biphenol with six chlorine atoms • Used in germicidal soaps • With possible neurotoxicity
  11. 11. Damage Cell MembraneDamage Cell Membrane C.C.Alcohols – also denatures proteinsAlcohols – also denatures proteins 1. Ethanol • Bactericidal • Remove lipid from skin surface • Widely used to clean the skin before immunization or venipuncture • Requires presence of water for maximal activity  more effective at 70%
  12. 12. Damage Cell MembraneDamage Cell Membrane C.C.Alcohols – also denatures proteinsAlcohols – also denatures proteins 2. Isopropyl alcohol • Greater bactericidal activity than ethanol; less volatile • Side effect: narcosis due to inhalation of fumes 2. Benzyl alcohol – used as preservative
  13. 13. Denaturation of Cellular ProteinsDenaturation of Cellular Proteins 1. Acids and alkali • Strong acids and alkali – bactericidal • Mycobacteria – resistant to 2% NaOH (used in clinical laboratory to liquefy sputum prior to culture) • Weak acids (benzoic, propionic, and citric acids) – used as food preservatives 2. Alcohol and acetone 3. Phenol and cresol
  14. 14. Modify Functional Groups of Proteins andModify Functional Groups of Proteins and Nucleic acids:Nucleic acids: A.A.Heavy Metals – damage enzyme activity ofHeavy Metals – damage enzyme activity of bacteria by binding to sulfhydryl groupsbacteria by binding to sulfhydryl groups 1. Mercurials • Example: thimesoral (merthiolate) & merbromin (mercurochrome)  skin antiseptics 2. Silver compounds • Bactericidal • 1% silver nitrate – ophthalmia neonatorum (Crede’s prophylaxis) • Silver sulfadiazine – burn wounds
  15. 15. Modify Functional Groups of Proteins and NucleicModify Functional Groups of Proteins and Nucleic acids:acids: B.B.Halogens – oxidizing agentsHalogens – oxidizing agents  inactivateinactivate enzymesenzymes 1. Iodine • Inactivates sulfhydryl-containing enzymes • Also binds specifically to tyrosine residues in proteins • Best antiseptic sporicidal, bactericidal, fungicidal, viricidal, amoebicidal • Used prior to obtaining a blood culture and installing IV catheters
  16. 16. Modify Functional Groups of Proteins and NucleicModify Functional Groups of Proteins and Nucleic acids:acids: B.B.Halogens – oxidizing agentsHalogens – oxidizing agents  inactivateinactivate enzymesenzymes 1. Iodine • Two forms: a) Tincture of iodine  2% iodine solution + potassium iodide in ethanol  Used to prepare skin prior to blood culture a) Iodophors  Complexes of iodine with detergents (e.g. Betadine)  Used to prepare skin prior to surgery; less irritating
  17. 17. Modify Functional Groups of Proteins and NucleicModify Functional Groups of Proteins and Nucleic acids:acids: B.B.Halogens – oxidizing agentsHalogens – oxidizing agents  inactivate enzymesinactivate enzymes 2. Chlorine • Kills by cross-linking essential sulfhydryl groups in enzymes  form inactive disulfide • For water treatment • Hypochlorite (HOCl) – sanitize dairy & food processing equipment; household disinfectant
  18. 18. Modify Functional Groups of Proteins and NucleicModify Functional Groups of Proteins and Nucleic acids:acids: B.B.Halogens – oxidizing agentsHalogens – oxidizing agents  inactivateinactivate enzymesenzymes 3. Hydrogen peroxide (H2O2) • Wound cleansing; surgical devices and soft plastic contact lenses • Effectiveness limited by the organism’s ability to produce catalase • Attacks sulfhydryl groups
  19. 19. Modify Functional Groups of Proteins andModify Functional Groups of Proteins and Nucleic acids:Nucleic acids: C.C.Alkylating agentsAlkylating agents 1. Formaldehyde • Sporicidal • Commercially available as formalin (37% solution in water) • Hydroxymethyl group of formaldehyde causes alkylation of –NH2 and –OH groups of nucleic acids • For preservation of specimens and preparation of vaccines • Kill Mycobacterium tuberculosis in sputum and fungi in athlete’s foot
  20. 20. Modify Functional Groups of Proteins andModify Functional Groups of Proteins and Nucleic acids:Nucleic acids: C.C.Alkylating agentsAlkylating agents 2. Glutaraldehyde • Sporicidal; with two reactive aldehyde groups • 10X more effective than formaldehyde • Used as cold sterilant • Medical equipments like respiratory therapy machines and other equipment that can be damaged by heat
  21. 21. Modify Functional Groups of Proteins andModify Functional Groups of Proteins and Nucleic acids:Nucleic acids: C.C.Alkylating agentsAlkylating agents 3. Ethylene oxide • Sporicidal • Hydroxyethyl group attacks the reactive hydrogen atoms on essential amino acids and hydroxyl groups • Used in gaseous sterilization of heat- sensitive materials or equipments like heart-lung machine and polyethylene tubes in anesthesia machines • Potentially carcinogenic

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