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