Chemical Methods Of Disinfection

• 1. Chemical Methods of Disinfection Fe A. Bartolome, MD, FPASMAP Department of Microbiology Our Lady of Fatima University

2.

• Sterilization

• • Killing of all microorganisms, including bacterial spores

• Disinfection

• • Reducing the number of bacteria to a level low enough that disease is unlikely to occur

• • Some organisms and bacterial spores may survive

3.

• Antiseptics

• • Chemicals used to kill micro-organisms on the surface of skin and mucous membranes

4.

• 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

5.

• Factors that affect efficacy of a chemical agent:

• • Concentration of chemical agent

• • • Higher concentration bactericidal EXCEPT alcohol (50% - 80%)

• • Time

• • • Longer time of exposure, better killing action

• • Temperature

• • • High temperature speeds up rate of chemical reaction

• • Nature of surrounding medium

• • • pH of medium; presence of extraneous materials like pus or blood

• • Nature of the organism

• • • Ability to produce spores; number & size of inoculum

6.

• Characteristics of a good chemical disinfectant or antiseptic:

• • Able to destroy a wide variety of microorganisms

• • Fast-actingshort contact time

• • Not affected by the presence of other substances such as organic matter

• • Non-toxic to human tissues as well as non-corrosiveand non-destructive to materials for which it is used

• • Should leave a residual antimicrobial film on the treated surface

• • Water-soluble and easy to apply

• • Inexpensive and easy to prepare

• • Stable under storage and shipping conditions

• • Odorless

7.

• Damage Cell Membrane

• Surface active agents interact with the lipid in the cell membranedisrupt cell membrane

• • Cationic agents

• • • Quarternary ammonium compounds

• • • Cationic detergents widely used for skin antisepsis

• • • Effective at alkaline pH

• • • Example: zephiran, benzalkonium chloride

8.

• Damage Cell Membrane

• Surface active agents

• • 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.

• Damage Cell Membrane

• Phenolic compounds also denature proteins

• • 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.

• Damage Cell Membrane

• Phenolic compounds

• • Cresols (Methylphenol)

• • • Phenol derivatives

• • • More potent and safer

• • • Example: lysol

• • Hexachlorophene

• • • Biphenol with six chlorine atoms

• • • Used in germicidal soaps

• • • With possible neurotoxicity

11.

• Damage Cell Membrane

• Alcohols also denatures proteins

• • Ethanol

• • • Bactericidal

• • • Remove lipid from skin surface

• • • Widely used to clean the skin before immunization or venipuncture

• • • Requires presence of water for maximal activitymore effective at 70%

12.

• Damage Cell Membrane

• Alcohols also denatures proteins

• • Isopropyl alcohol

• • • Greater bactericidal activity than ethanol; less volatile

• • • Side effect: narcosis due to inhalation of fumes

• • Benzyl alcohol used as preservative

13.

• Denaturation of Cellular Proteins

• • 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

• • Alcohol and acetone

• • Phenol and cresol

14.

• Modify Functional Groups of Proteins and Nucleic acids:

• Heavy Metals damage enzyme activity of bacteria by binding to sulfhydryl groups

• • Mercurials

• • • Example: thimesoral (merthiolate) & merbromin (mercurochrome)skin antiseptics

• • Silver compounds

• • • Bactericidal

• • • 1% silver nitrate ophthalmia neonatorum (Credes prophylaxis)

• • • Silver sulfadiazine burn wounds

15.

• Modify Functional Groups of Proteins and Nucleic acids:

• Halogens oxidizing agentsinactivate enzymes

• • 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.

• Modify Functional Groups of Proteins and Nucleic acids:

• Halogens oxidizing agentsinactivate enzymes

• • Iodine

• • • Two forms:

• • • • Tincture of iodine

• • • • • 2% iodine solution + potassium iodide in ethanol

• • • • • Used to prepare skin prior to blood culture

• • • • Iodophors

• • • • • Complexes of iodine with detergents (e.g. Betadine)

• • • • • Used to prepare skin prior to surgery; less irritating

17.

• Modify Functional Groups of Proteins and Nucleic acids:

• Halogens oxidizing agentsinactivate enzymes

• • Chlorine

• • • Kills by cross-linking essential sulfhydryl groups in enzymesform inactive disulfide

• • • For water treatment

• • • Hypochlorite (HOCl) sanitize dairy & food processing equipment; household disinfectant

18.

• Modify Functional Groups of Proteins and Nucleic acids:

• Halogens oxidizing agentsinactivate enzymes

• • Hydrogen peroxide (H 2 O 2 )

• • • Wound cleansing; surgical devices and soft plastic contact lenses

• • • Effectiveness limited by the organisms ability to produce catalase

• • • Attacks sulfhydryl groups

19.

• Modify Functional Groups of Proteins and Nucleic acids:

• Alkylating agents

• • 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

• • • KillMycobacterium tuberculosisin sputum and fungi in athletes foot

20.

• Modify Functional Groups of Proteins and Nucleic acids:

• Alkylating agents

• • 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.

• Modify Functional Groups of Proteins and Nucleic acids:

• Alkylating agents

• • 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