DISINFECTION DEFINITION: The freeing of an article from some living organisms, i.e. killing many but not all micro- organisms.

METHODS: 1. Heat To disinfect eating utensils and clothing at a temp. of 70˚C for several minutes. 2. Chemical Commonly used : phenol & Drawback : liable to be rendered inactive by undue dilution, by contact with organic matter (dirt, pus, blood).

CLASSIFICATION : 1. Strong Very potent, but toxic to Not used for skin or tissues (formalin) 2. Mild Disinfectants Applied to tissue & skin ( alcohol, iodine, soap ) By definition : an antiseptic is a chemical used to kill organisms on skin & mucous membranes.

FACTORS INFLUENCING DISINFECTION : 1. Concentration of disinfectant Disinfectant is used at its right concentration and dilution. 2. Time of Depends on nature & concentration of disinfectant. 3. Number of organisms present.

4. Nature of organisms present e.g.: vegetative forms or spore- Doubtful action on endospores. 5. Presence of Increases rate of action of disinfectant. 6. pH of Action depends on correct pH.

7. Hardness of water some antiseptics are affected by hard water (soap) 8.Organic matter Reduces efficiency of a disinfectant (pus, blood, dirt).

ADVANTAGES Before disposal or re-use Bed-pan, clothes, clinical thermometer, tongue depressor, specula, slides, Best : phenol and hypochlorite. 2.Reduction of environment microbes Floor, walls, furniture, theater, Kitchen: soap, phenol, hypochlorite, Room : by formaldehyde gas. 3.Skin, hands & operation site Use soap, chlorhexidine, iodine, alcohol

PROPERTIES AND USES OF DISINFECTANTS 1.Phenol Phenol (carbolic acid) : cheap, powerful, microbicidal, active against many organisms, not affected by organic matter (include: lysol, Chlorophenols (Dettol) : less toxic, affected by organic matter

2. The Bactericidal : chlorine and iodine * Chlorine: to disinfect water, affected by organic matter, e.g. : Eusol: used in hospitals. Hypochlorite (Clorox): not applied to cloth or to metal. * Iodine: Affected by organic matter, powerful, rapid disinfectant, irritant.

3. Metallic salts: a)Mercuric Bacteriostatic, used to inactivate vaccines, to preserve antitoxins and anti-sera. b) Silver nitrate: used for extensive burns.

4. Formaldehyde+ kills organisms & spores, cheap, used as gas to disinfect rooms, & as solution to sterilize Glutaraldehyde: active against spores, used for cystoscopes, thermometers, plastic materials.

5. Volatile solvents: a)Isopropyl & ethyl Bactericidal at dilution 70-75%, action is lowered when absolute, or when over-diluted, used for injections & drips. b) Acetone & ether Weak as a disinfectant c) Bactericidal, disappears quickly when applied, not widely used.

6. Soap & Soap: mechanical removal of organisms on Other detergents : ammonium compounds are Cetrimide (Cetavlon): inactive against Pseudomonas.

7. Aniline & acridine Active against gram +ve organisms, bactericidal, used in presence of organic Gentian violet: used for burns.

GASEOUS DISINFECTANTS: 1. Formaldehyde Used to sterilize air in rooms, Exposure to continue for 3 Spray ammonia to remove formaldehyde residues. 2. Ethylene Kills organisms & spores, used for plastic & rubber articles, Toxic, explosive when mixed with air,

TESTS OF DISINFECTANTS: 1. Rideal-Walker Test. 2. Chick-Martin Test 3. Determination of the number of viable organisms after application of disinfectant by bacterial count technique.

Rideal-Walker & Chick-Martin Apply phenol coefficient which is a quantitative measurement of the ability of a disinfectant to kill a micro-organism. By definition: a phenol coefficient is a ratio of concentration of phenol to concentration of disinfectant required to give same amount of killing under standard conditions i.e. Phenol coefficient ratio = Concentration of phenol Concentration of disinfectant

MECHANISM OF ACTION 1. Disruption of cell Alcohol: disorganizes lipid structure of cell membrane & denatures cell Detergents: interact with lipid layer of cell Phenols: damage cell membrane & denature proteins.

2. Modification of proteins: a)Chlorine: interact with cell enzymes to form the inactive disulphide compound. b) Iodine: inactivates cell enzymes & denatures cell proteins. c) Heavy metals: block cell enzyme activity, i.e. Hg & Ag.

d) Hydrogen peroxide: inhibits enzymatic activity of cell. e) Formaldehyde: denature proteins & nucleic acids. f) Glutaraldehyde: same action as formaldehyde, ten times more effective. g) Ethylene oxide: denature proteins and modifies nucleic acids of cell. h) Strong acids & alkalis: H 2 SO4 and Na OH denature proteins.

3. Nucleic acids Modification : a) Crystal (gentian) violet dye : Binds to the phosphate group of nucleic acid. b) Malachite green dye: has same action as crystal violet.