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

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

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

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

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

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

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

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

9. 2. The halogens: @ 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.

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

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

12. 5. Volatile solvents: a)Isopropyl & ethyl alcohol: @ 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) Chloroform: @ Bactericidal, disappears quickly when applied, not widely used.

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

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

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

16. 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.

17. Rideal-Walker & Chick-Martin tests: @ 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

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

19. 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.

20. 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.

21. 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.