1. CHEMICAL METHODS PRAVEG GUPTA

2. WHY NEEDED? Microorganisms are ubiquitous. Since they causecontamination, infection anddecay, it becomes necessary toremove or destroy them frommaterials or from areas. This is the object of sterilization. 3. The process of sterilization is used in microbiology for preventing contamination byextraneous organisms, in surgery for maintaining asepsis, in food and drug manufacture for ensuring safety fromcontaminating organisms, and in many other situations. The methods of sterilization employed depend on the purpose for which it is carried out, the material which has to be sterilized and the nature of the microorganisms that are to be removed ordestroyed. 4. DEFINITIONS Sterilization process by which an article, surface ormedium is freed of all living microorganisms either in thevegetative or spore state. Disinfection destruction or removal of all pathogenicorganisms. (sanitization w.r.t. Food processing andcatering) 5. Antisepsis prevention of infection, usually by inhibitingthe growth of bacteria in wounds or tissues. Antiseptics chemical disinfectants which can be safelyapplied to skin or mucous membrane and are used toprevent infection by inhibiting growth of bacteria. Bactericidal agent which can kill bacteria. Bacteriostatic agent which only prevents multiplicationof bacteria. 6. PHYSICAL AGENTS Sunlight Drying Dry heat flaming, incineration, hot air. Moist heat pasteurization, boiling, steamunder normal pressure, steam under pressure. Filtration candles, asbestospads, membranes. Radiation Ultrasonic and sonic vibrations. 7. CHEMICAL AGENTS Alcohols ethyl, isopropyl, trichlorobutanol Aldehydes formaldehyde, glutaraldehyde Dyes Halogens Phenols Surface active agents Metallic salts Gases ethylene oxide, formaldehyde, betapropiolactone. 8. IDEAL CHEMICAL DISNIFECTANT An ideal chemical antiseptic or disinfectant should have thefollowing properties: Wide spectrum of activity Active in the presence of organic matter Effective in acid as well as alkaline media Speedy action High penetrating power Stable Compatible with other antiseptics and disinfectants Not corrode metals Not cause local irritation or sensitization Not interfere with healing Not be toxic if absorbed into circulation Cheap and easily available Safe and easy to use 9. MODES OF ACTION OF CHEMICAL DISINFECTANTS Protein coagulation Disruption of cell membrane resulting in exposure, damage or loss of the contents. Removal of free sulphydryl groups essential for the functioning of the enzymes. Substrate competition a compound resembling the essential substrate of the enzyme diverts or misleads the enzymes necessary for the metabolism of the cell and causes cell death. 10. ALCOHOLS Ethanol (80% v/v ethyl alcohol)or 2-propanol (60-70% v/v iso-propyl alcohol) solutions areused to disinfect skin anddecontaminate cleansurfaces. Spectrum: Effective againstfungi, vegetativebacteria, Mycobacterium speciesand some lipid-containingviruses. 11. Limitation: Not effective against spores.Concentration: Most effective at 70% inwater.Caution: Do not use near flames due toflammability.May swell rubber or harden plastics. 12. ALDEHYDES FORMALDELYDE: Precautions are required whenhandling formaldehyde Formalin is 37% w/v formaldehyde gas in water. Spectrum: Active against most microorganisms. Bactericidal, sporicidal, virucidal. 13% v/v formalin is a good decontaminant (but has anirritating odour). 8% v/v formalin in 80% v/v alcohol is effective againstvegetative bacteria, spores and viruses. Does not corrode stainless steel. 13. Uses: Formaldehyde is used to preserve anatomicalspecimens, and for destroying anthrax spores in hairand wool. 10% formalin containing 0.5% sodium tetraborate is usedto sterilize clean metal instruments. Formaldehyde gas is used to sterilize instruments, heatsensitive catheters and for fumigation of wards, sickrooms and laboratories. It can also be used for clothing, bedding, furniture andbooks. To disinfect equipment such as centrifuges or biosafetycabinets. 14. Metal instruments, biosafetycabinets, clothing, bedding, furniture and books 15. FUMIGATION TECHNIQUE After sealing the windows and other outlets, formaldehydegas is generated by adding 250g of KMnO4 to 500 mlformalin for every 1000 cu.ft of room volume. Caution: The reaction produces considerable heat, and soheat resistant vessels should be used. After starting generation of formaldehyde vapour, thedoors should be sealed and left unopened for 48 hours. Caution: Formaldehyde can react with free chlorine toproduce toxic gas. Remove hypochlorite solutions andhydrochloric acid from spaces to be decontaminated. Irritant vapours are released hence Neutralise withammonia following decontamination. 16. FUMIGATION 17. GLUTARALDEHYDE: Concentration: Glutaraldehyde is commercially availableas 2% w/v aqueous solution which must be made alkalineto "activate" (e.g. by addition of 0.3% sodium bicarbonate). A 2% glutaraldehyde solution, for at least 10 hours, can beused to sterilize heat labile items. Spectrum: Active against vegetative bacteria, spores, fungiand many viruses. Note: Also available in stable glycocomplexed form whichdoes not require addition of alkaline buffer. 18. Use: for instruments such ascystoscopes, bronchoscopes, corrugated rubber anesthetictubes, face masks, endotracheal tubes, metalinstruments, polythene tubing. 19. Caution: Glutaraldehyde is known to cause dermatitis andasthma. Less irritating than formaldehyde. Glutaraldehyde should not be used in an area withlittle or no ventilation. Eye protection, a plastic apron, and gloves must beworn Should be stored away from heat sources and incontainers with close-fitting lids. The length of time that glutaraldehyde solutions canbe used varies but they are usually good for up to 14days. Solutions should be replaced any time they becomecloudy. 20. GlutaraldehydeAdvantages Numerous use studies published Relatively inexpensive Excellent materials compatibilityDisadvantages: Pungent and irritating odor Relatively slow mycobactericidal activity Coagulate blood and fix tissues to surfaces 21. CHLORINE COMPOUNDS Generally used in the form of sodium hypochlorite. Effective against a wide variety of microorganisms(vegetative bacteria and viruses). Preferred disinfectantfor HIV and hepatitis viruses. Concentration: Use at 0.1% as a general disinfectant. Effective between a pH range of 6-8. 22. Limitations: Less suitable in the presence of organic matter (such asblood). Concentration must be increased to retain action(0.5%). Strength decreases on standing (make fresh solutionsdaily). High concentrations corrode metal surfaces, andbleach and damage fabrics. 23. HYPOCHLORITE: These are inexpensive, broad spectrum chlorine releasingdisinfectants of choice against viruses, including hepatitisB virus. Aqueous solution of sodium hypochlorite (5.25%) is calledhousehold bleach. It is used in a concentration of 0.2-1% depending upon thecircumstances. Caution: hypochlorites are inactivated by organicmatter. They corrode metals, hence contact of thechemical with the metallic instruments and equipmentmust be avoided. 24. In case of heavy soilage egblood spillage, aconcentration of 10000ppm (1:5 dilution ofhousehold bleach) ofavailable chlorine isrecommended. Uses: it has greatwidespread use as alaboratory disinfectanton surfaces of bench and indiscard spots. 25. IODINE COMPOUNDS Iodine is used in aqueous or alcoholic solution. Rapidly effective against most microorganisms. Concentration: Usually diluted to 1% w/v freeiodine, optimum pH neutral to acid. Caution: Not suitable in the presence of organic matter. Stains skin and may cause irritation. Decomposes when heated above 40C. Do not use on aluminium or copper. 26. Method of use: Dilute inalcohol for washinghands, or use as asporicide. Prepare dilutions daily. Use: Most commonly usedfor skin disinfection anddecontaminating cleansurfaces. 27. Iodophores: They have largely replaced the aqueous and tincture formsof iodine since the side effects like staining and irritationare far less in iodophores than in aqueous or tinctureiodine. Iodophores are chemical complexes with iodine bound to acarrier such as polyvinylpyrolidone (povidone, PVP) orethoxylated nonionic detergents. Free microbicidal iodine is gradually released from thesecompounds. 28. Commercial PVP in a dilution of 1:2 to 1:100 kills most bacteria including S.aureus. Limitation: may become contaminated by organisms like pseudomonas. Uses: iodophors are widely used for antisepsis of skin, mucosa and wounds. A 2.5% ophthalmic solution is an useful prophylactic against neonatal conjunctivitis. 29. CHLORHEXIDINE (hibitane) Chlorhexidine as chlorhexidine gluconate is dissolved in70% alcohol. Effective against Gram-positive organisms and HIV. Active in ph range 5.5 - 8.0. Limitation: Not recommended as a general disinfectant. Not active against sporulating bacteria or non-lipid-containing viruses. Incompatible with soap and anionic detergents. 30. Use: savlon (chlorhexidine+cetrimid e) is widely used in burns, wounds, as bladder irrigant, for surgical instruments and pre-operative disinfection of skin. Use as antiseptic. Apply alcoholic chlorhexidine to the skin in the event of accidental contamination. 31. HYDROGEN PEROXIDE A concentration of 3% w/vgenerally used fordisinfection. Active against a range ofmicroorganisms. Fungi, spores and entericviruses require higherconcentration. No toxic end-products ofdecomposition. 32. Caution: Do not use onaluminium, copper, zinc orbrass. Mechanism: H2O2 ondecomposition liberatesfree hydroxyl radical whichis the active ingredient inthe process. Use: H2O2 is applied todisinfect plasticimplants, contactlenses, and surgicalprostheses. 33. PHENOLICS Synthetic phenolics (clear solublefluids) can be used as generaldisinfectants in the laboratory. Spectrum: Active against bacteriaand lipid-containing viruses. Not active against spores and non-lipid-containing viruses. Active in presence of organic matter. Use: for disinfectingfloors, walls, benches and otherfurniture. 34. Cresols: (methylphenols, lysol) Limitation: toxic to skin andtissues. Use: mainly used forpreliminary sterilization ofinfected glasswares inlaboratory, disinfection ofexcreta, cleaning floors ofwards and operation roomin hospital. Chloroxylenol (dimethylphenol) is active ingredientof dettol. 35. Hexachlorophane: it isbacteriostatic at very highdilutions and used in soap andpowder form. It is more effectiveagainst gram positive than gramnegative bacteria and is appliedon skin as prophylaxis againststaphylococcal infection. Chlorhexidine: mentionedpreviously 36. QUATERNARY AMMONIUM COMPOUNDS Quaternary ammonium compounds are positively charged(cationic) surface-active disinfectants. Effective against Gram-positive bacteria and lipid-containing viruses. Not recommended as general disinfectants (they have anarrow antibacterial spectrum). Inactivated by proteins, soap and anionic detergents. Eg. Benzalkonium chloride, alkyldimethylbenzylammonium chloride, and cetylpyridinium chloride. Used for cleaning of floors of hospitals. 37. ETHYLENE OXIDE It is an alkylating agent. Exerts lethal effect on proteins of bacteria. It is gas at ordinary room temperature and active against alltypes of bacteria and spores. It has got a good degree of penetration power, even throughplastics. 38. ETO Machine Uses: Plasticgoods, polythene tube, arteryand bonegrafts, cystoscopes, vaccinesand culture media can besterilized by ethylene oxide. These objects are kept in acabinet from which air isremoved by a vacuum pump andthen a mixture of ethylene oxideand carbon dioxide isintroduced in the cabinet. 39. BETAPROPIOLACTONE (BPL) It is a condensation product of ketone and formaldehydehaving a boiling point of 163C. It is capable of killing all microorganisms including viruses. Uses: Although BPL has a low penetrating power as agas, but it is believed to be more efficient for the purpose offumigation. Its biocidal action is very rapid and only 0.2% BPL is usedfor the sterilization of biological products. Limitation: unfortunately BPL has carcinogenic effect. 40. Points to ponder Prepare fresh dilutions daily Use clean, dry containers Use clean water for dilutions Use higher concentration or for longer duration if spillageis heavy. Avoid using corrosive disinfectants on metal surfaces. 41. THANK YOU