CHEMICAL CONTROL OF MICROORGANISMS

1. CHEMICAL CONTROL OFMICROORGANISMS

2. LEARNING OBJECTIVES At the end of the topic, students will be able to; • Differentiate between Sterilization & Disinfection. • Differentiate between Antiseptics & Disinfectants. • List the properties of an ideal Disinfectant/ Antiseptic. • Differentiate halogens used as antiseptics from halogens used as disinfectants. • Identify the methods of action and preferred uses of chemical disinfectants. • Identify the appropriate uses for surface-active agents.

3. DISINFECTION Disinfection is the elimination of pathogens, except spores, from inanimate objects. Disinfectants are chemical agents used to clean inanimate objects. If the object is lifeless such as table top, the chemical agent is known as DISINFECTANT. However, if the object is living, such as tissue of the human body, the chemical is an Antiseptic.

4. THE IDEAL DISIFECTANT • Must be able to kill microorganisms. • non-toxic to animals or humans esp. if used as antiseptic. • Should be soluble in water. • Resistant to inactivation. • Should be useful in very diluted form and perform its job in a relatively short time. • Stable. • Penetrating. • Not corrode instruments. • Easy to obtain. • Inexpensive.

5. CHEMICAL CONTROL OF MICROBIAL AGENTS IMPORTANT CHEMICAL AGENTS: • Halogens. • Phenol and phenolic compounds. • Heavy metals. • Alcohols.

6. OTHER CHEMICAL AGENTS: • Formaldehyde. • Glutaraldehyde. • Ethylene oxide. • Beta propiolactone. • Hydrogen peroxide. • Soap and detergents. • Dyes. • Acids.

7. HALOGENS • Iodine • Chlorine

8. IODINE One of the oldest and most effective germicidal agents. It inhibits protein synthesis and oxidizes –SH groups of amino acids. Also Halogenates tyrosine in protein. Tincture of Iodine (2% I2+2% Na2I in 70% alcohol) is a commonly used antiseptic for wounds. Continue…

9. IODINE • Iodine is also used in the form of a substance known as Iodophors • Iodophors are mixtures of iodine with surface active agents which acts as carriers and solubilizers for the iodine. One of these agents is PVP (polyvinylpyrrolidone) • The complex can be expressed as PVP-I. • Iodine is released slowly from this complex and thus reduce the irritation of the antiseptic.

10. CHLORINE • Most widely used disinfectants. • Chlorine is powerful oxidizing agent that kills by cross-linking essential sulfhydryl groups in enzymes to form the inactive sulfide. • Used as a disinfectant to purify the water supply and to treat swimming pools , where it keeps bacterial populations at low levels. • Not sporicidal.

11. CHLORINE • It is also the active component of hypochlorite, which is used as a disinfectant in home and hospitals. • Hypochlorite compounds release free chlorine in solution. • Sodium hypochlorite (NaOCl) also known as Bleach. • Calcium hypochlorite [Ca(OCl)2] also known as Chlorinated lime.

12. CHLORINE • Cloramine, such as Chloramine-T, are organic compounds that contain chlorine. • These compounds release free chlorine more slowly than hypochlorite sol. and are more stable. • They are valuable for general wound antiseptics and root canal therapy.

13. PHENOL & PHENOLICS

14. PHENOL & PHENOLIC COMPOUNDS • Damage membrane, inactive enzymes, denature proteins. • Very effective disinfectants. • A 5% aqueous solution of phenol rapidly kills the vegetative cells of microorganisms BUT spores are much more resistant.

15. PHENOL & PHENOLIC COMPOUNDS • Cresol (phenol derv.) have greater germicidal activity and lower toxicity than the parent compound. • Hexyl Resorcinol (another phenol derv.), is marketed in a solution of glycerin & water, used in mouth wash and topical antiseptic & in throat lozenges.

16. PHENOL & PHENOLIC COMPOUNDS • Bisphenols… combination of two phenol molecules, are prominent in modern disinfection and antiseptics. Examples: • Orthophenylphenol e.g. is used in Lysol (a saponified cresol) • Hexachlorophene, was used extensively during the 1950s & 1960s in tooth paste, under arm deodorant and bath soap. • Chlorhexidine, 4% sol in isopropyl alcohol, used as a surgical scrub, hand wash and superficial skin wound cleanser. Continue…

17. Chloroxylenol (Dettol) • A bisphenol in wide spread use is Trichlosan, a broad spectrum anti microbial agent, that destroys bacteria by disrupting cell membrane (& possibly, cell wall) by blocking the synthesis of lipids. • The chemical is included in antibacterial soaps, lotions, mouth washes, tooth pastes & kitchen sponges.

18. sss PHENOL CO-EFFICIENT • Phenol has the additional distinction of being the standard against which other disinfectants of a similar chemical structure are compared to determine their antimicrobial activity. • PC is a number that indicates the disinfecting ability of an antiseptic or disinfectant in comparison to phenol under identical conditions. • A PC higher than 1 indicates that the chemical is more effective than phenol. • PC less than 1 indicates poorer disinfecting ability than phenol.

19. PC OF SOME COMMON ANTISEPTICS & DISINFECTANTS

20. HEAVY METALS • Mercury, silver, copper. • Act by precipitation of proteins and oxidation of sulfhydryl groups. • Bacteriostatic.

21. MERCURY • Mercuric chloride • For treating skin diseases. • V.toxic to the host. • Anti microbial activity of mercury is reduced when other organic matter is present. • THIMEROSAL (mercury derv.), previously used as a preservative in vaccine.

22. COPPER • Active against chlorophyll containing organisms. • Potent inhibitor of algae. • Copper sulfate, incorporated in to algicides and is used in swimming pools and municipal water supplies. • CuSO4 is also mixed with lime to form the bluish-white Bordeaux mixture used since 1882, to control the growth of fungi.

23. SILVER • Silver nitrate • Skin antiseptic. • 1% AgNO3 solution may be placed in the eyes of newborns to protect against infection by Neisseria gonorrhoeae. • Silver sulfadiazine is used to prevent infections by burn wounds.

24. INFECTED EYE OF NEW BORN BY Neisseria gonorrhoeae.

25. ALCOHOL

26. ALCOHOLS • Mode of action: Alcohols dehydrate cells, disrupt membranes and cause coagulation of protein. • Examples: Ethyl alcohol, isopropyl alcohol and methyl alcohol • Application: A 70% aqueous solution is more effective at killing microbes than absolute alcohols. • 70% ethyl alcohol (spirit) is used as antiseptic on skin. continue…

27. Propyl & IPA in conc. ranging from 40-80% are bactericidal for vegetative cells. • IPA or rubbing alcohol, has high bactericidal activity in conc. as high as 99% • used to disinfect clinical thermometers.

28. Methyl alcohol is less bactericidal than ethyl alcohol. • Methyl alcohol kills fungal spores, hence is useful in disinfecting inoculation hoods. • Methyl alcohol is toxic to tissues and is used infrequently. • Methyl alcohol is highly poisonous, even the fumes of this compound may produce permanent injury to the eyes.

29. ALDEHYDE • FORMALDEHYDE • GLUTARALDEHYDE

30. FORMALDEHYDE • HCHO • Reacts with functional group in proteins & nucleic acids. • FORMALIN: 37% solution in water. • In Microbiology, formalin is used for inactivating viruses in certain vaccines. Continue…

31. In gaseous form, formaldehyde is expelled into a closed chamber where it is a sterilizing agent for surgical equipments, hospital gowns & medical instruments. • Penetration is poor and the surface must be exposed to the gas for up to 12 hrs for effective sterilization. • Formaldehyde leaves a residue, and instruments must be rinsed before use.

32. GLUTARALDEHYDE • Reacts with functional group in proteins & nucleic acids. • 2% sol. of this chemical (Cidex) exhibits a wide spectrum of antimicrobial activity. • Effective against vegetative bacteria, fungi, bacterial & fungal spores and viruses. • Glutaraldehyde is 10 times more effective than formaldehyde & is less toxic. • For sterilizing urological instruments, respiratory therapy equipments & other special equipments.

33. ETHYLENE OXIDE • Mode of action: It is an alkylating agent. • It acts by alkylating sulfydryl-, amino-, carboxyl- and hydroxyl- groups. • EtO is liquid at temp below 10.8oC. Above this temp. , it vaporizes rapidly. • Excellent penetration capacity & sporicidal activity. • Toxic & highly explosive. • Since it is highly flammable, it is usually combined with CO2 (10% CO2+ 90% EO) Continue…

34. ETHYLENE OXIDE • It is an effective sterilizing agent for heat & moisture sensitive materials. • EtO is used to sterilize papers, leather, wood, metal and rubber products as well as plastics. • In hospitals, it is used to sterilize catheters, artificial heart valves, heart-lung machine components & other optical equipment.

35. ETHYLENE OXIDE

36. BETA-PROPIOLACTONE • It is an alkylating agent and acts through alkylation of carboxyl- and hydroxyl- groups. • It is a colorless liquid with pungent to slightly sweetish smell. • It is an effective sporicidal agent, and has broad-spectrum activity. • 0.2% is used to sterilize biological products. • It is used to sterilize vaccines, sera & surgical instruments. • Disadvantages: It has poor penetrating power and is a carcinogen.

37. HYDROGEN PEROXIDE • It is an oxidizing agent that attacks sulfhydryl groups, thereby inhibiting enzymatic activity. • Used as antiseptic to clean wounds. • Used to disinfect contact lenses. • Its effectiveness is limited because bacteria and body tissues contain enzymes (catalase) that inactivate hydrogen peroxide. • Sterilization can also be achieved after 6 hrs of exposure to a 6% solution.

38. SOAPS AND DETERGENTS • A soap is a chemical compound of fatty acids combined with potassium or hydrogen peroxide. • The pH of the compound is usually about 8.0 & some microbial destruction is therefore due to the alkaline conditions established on the skin. • However, the major activity of the soap is as a de-germing agent for the mechanical removal of m.org. from the skin surface. • Soaps are ‘wetting agents’, i.e. they emulsify & solubilize particles clinging to a surface.

39. Detergents are synthetic chemicals acting as strong wetting agent & surface tension reducers. • While soaps are always negatively charged, some detergents are negatively charged while others are positively charged. • One example of a positively charged detergent are quaternary ammonium compounds (also known as quats)

40. QUATS • Quats are cationic detergents that act by disrupting lipid bilayers.

41. MOA • They have the property of concentrating at interfaces between lipid containing membrane of bacterial cell and surrounding aqueous medium. • These compounds have long chain hydrocarbons that are fat soluble and charged ions that are water-soluble. Since they contain both of these, they concentrate on the surface of membranes. They disrupt membrane resulting in leakage of cell constituents.

42. QUATS • Bacteriostatic. • Quats are most effective against Gram-positive bacteria • Quats do not kill endospores, Mycobacteria spp., nor non-enveloped viruses • Zephiran  Benzalkonium chloride • Cepacol Cetylpyridinium chloride

43. USES: • As sanitizing agents for industrial equipment & food utensils. • as skin antiseptics. • in mouth washes. • storage solution for contact lenses. • For disinfecting hospital walls & floors.

44. DYES • TRIPHENYLMETHANE DYES: • Crystal violet • Malachite green • ACRIDINE DYES: • Acriflavine • Proflavine

45. TRIPHENYLMETHANE DYES • As antiseptic against species of Bacillus & Staphylococcus. • As Gentian violet for trench mouth & for Candida albicans infection such as thrush. • MOA: interferes with the cell wall construction. • The dye is bactericidal at very weak dilutions of less than 1:10,000

46. ACRIDINE DYES • ACRIFLAVINE AND PROFLAVINE. • Used as antiseptics for staphylococcal infection in wounds. • Bactericidal • MOA: interact with bacterial nucleic acid

47. ACIDS • Benzoic acid • Salicylic acid • Organic acids are particularly valuable as food preservative. • Lactic & acetic acid e.g. are important preservatives in sour foods such as cheese & pickled products. • Propionic acid is added to bakery products to keep microbial population low.