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