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steriliz Presentation Transcript

  • 1. Chapter 11 Physical and Chemical Agents for Microbial Control
  • 2. Control of microbes Physical and chemical methods to destroy or reduce microbes in a given area
  • 3. OVERVIEW 3
  • 4. Why do we want to control microbes? How do we do it?
  • 5. Relative resistance of microbes Least resistance Highest resistance – Bacterial endospores – Prions Moderate resistance – Pseudomonas sp. – Mycobacterium tuberculosis – Staphylococcus aureus – Protozoan cysts – – – – – most vegetative cells Fungal spores enveloped viruses Yeast Protozoan trophozoites
  • 6. Methods that kill microbes _______________ – a process that destroys all viable microbes, including viruses & endospores – Heat, sterilants _______________– a process to destroy vegetative pathogens, not endospores – disinfectants or germicides – chemical - kills pathogenic microorganisms – _____________________ – destroy/inhibit vegetative pathogens on exposed body surfaces – Sepsis – infection/growth in body – Asepsis – preventing entry of pathogens and infection
  • 7. Methods that reduce numbers _______________– any cleansing technique that mechanically removes microbes and reduces numbers to safe levels – _______________– reduces the number of microbes on skin ___________________________ – controls numbers by preventing growth (multipication)
  • 8. 8
  • 9. Microbial death Permanent termination of an organism’s vital processes microbiological definition: Involves permanent loss of reproductive capability, even under optimum growth conditions
  • 10. Factors that influence microbial killing 10
  • 11. How antimicrobial agents work: Cellular targets of control (mode of action) 1. Cell wall 2. Cell membrane 3. Cellular synthetic processes (DNA, RNA) 4. Proteins
  • 12. mode of action Cell wall Action: – Block synthesis – Digestion – Disrupt surface w/o cell wall, bacteria will lyse (especially gram positive… remember?) Examples: penicillin, detergents, alcohol
  • 13. Surfactants disrupt mode of action
  • 14. mode of action Affect on synthesis (DNA, RNA) Proteins – have many functions in the cell! Antimicrobials can block: DNA synthesis (master code), transcription, translation  Mutagens (radiation = permanent inactivation of DNA)  Antimicrobial therapy (drugs)  Chemicals – some destroy nucleic acids
  • 15. mode of action Heat, pH, heavy metals can alter proteins
  • 16. Practical concerns Does the application require sterilization? Is the item to be reused? (time, $$) Can the item withstand heat, pressure, radiation, or chemicals? Is the method suitable? Will the agent penetrate to the necessary extent? Is the method cost- and labor-efficient & is it safe?
  • 17. Types of Control: I. Methods of Physical Control 1. Heat 2. Cold temperatures 3. Desiccation 4. Radiation 5. Filtration
  • 18. Physical Control 1. Heat Moist vs. dry Moist heat = lower temp and shorter time Causes coagulation/denaturation of protein Dry heat = higher temp/longer time Dehydrates cell, removes water, denatures proteins, oxidation (burning)
  • 19. Physical Control
  • 20. Physical Control 1. Heat – moist heat Moist heat uses hot water or steam sterilization  _______________ 15 psi/121oC/10-40min (steam under pressure)  intermittent sterilization – 100oC 30-60 min for 3 days (unpressurized steam) disinfection  Boiling at 100oC for 30 minutes to destroy nonspore-forming pathogens  _______________ kills Salmonella, Listeria & overall microbe count
  • 21. Physical Control
  • 22. Pasteurization Pasteurization – heat  kill potential agents of infection and spoilage without destroying the food flavor or value 63°C–66°C for 30 minutes (batch method) 71.6°C for 15 seconds (flash method) Not sterilization – kills non-sporeforming pathogens and lowers overall microbe count; does not kill endospores or many nonpathogenic microbes 22
  • 23. Physical Control 1. Heat – dry heat Dry heat uses higher temperatures than moist heat, can also sterilize incineration – 600-1200oC combusts & dehydrates cells dry ovens – 150-180oCcoagulate proteins
  • 24. Thermal death Physical Control Thermal death time (TDT) – shortest length of time required to kill all test microbes at a specified temperature Thermal death point (TDP) – lowest temperature required to kill all microbes in a sample in 10 minutes
  • 25. Physical Control 2. Cold temperatures _______________– slows the growth of microbes refrigeration 0-15oC & freezing <0oC used to ____________food, media and cultures
  • 26. Physical Control 3. Desiccation gradual removal of water from cells, leads to metabolic inhibition not effective microbial control – many cells retain ability to grow when water is reintroduced _______________ = freeze-drying Note: cold and dessication ARE NOT good methods of disinfection or sterilization.
  • 27. Physical Control 4. Radiation 1. _______________ radiation – deep penetrating power, breaks DNA – gamma rays, X-rays, cathode rays – used to sterilize medical supplies & food products 1. _______________ radiation – little penetrating power to sterilize air, water & solid surfaces – uv light creates thymine dimers, which interfere with replication
  • 28. Ionizing radiation Physical Control
  • 29. Nonionizing radiation - UV Physical Control
  • 30. UV treatment of wastewater Physical Control
  • 31. Physical Control Other “waves” Sound (high frequency) Can also be used to disrupt cells (vibrations) or generate heat Ultrasonic devices are used clean dental, medical instruments before sterilization
  • 32. 5. Filtration physical removal of microbes by passing a gas or liquid through filter Pores of filter large enough for liquid but too small for microbe (<1 μm) used to Physical Control
  • 33. OVERVIEW 33
  • 34. Types of Control: II. Methods of Chemical Control Categories: • Halogens • Phenolics • Chlorhexidine • Alcohols • Hydrogen peroxide • Detergents & soaps • Heavy metals • Aldehydes Uses: •Disinfectants •antiseptics •sterilants •degermers •preservatives
  • 35. Chemical antimicrobials 10,000 manufactured today About 1,000 routinely used Society is obsessed with “killing germs” – to the point of being excessive Result: widespread overuse  resistance of pathogens, death of natural flora
  • 36. Qualities of chemical antimicrobials Rapid action, even in low concentration Water/alcohol soluble, stabile Broad spectrum w/o being toxic Penetration, sustained action Resitance to inactivation Noncorrosive, nonstaining Sanitizing and deodorizing Inexpensive and available
  • 37. Levels of activity
  • 38. Factors that affect activity Type of microorganism being treated Material being treated Amt of contamination Exposure time Strength/action of germicide  Appendix C shows procedures for testing effectiveness
  • 39. Ways to express strength/concentration Dilution (1:200 is one part chemical in 200 parts dilutant such as water) ppm – parts per million Percent – 70% alcohol, or mg/ml _______________ solutions – have water as the solvent _______________– are dissolved in alcohol
  • 40. Chemical control - categories 1. 2. 3. 4. 5. 6. 7. 8. Halogens Phenolics Chlorhexidine Alcohols Hydrogen peroxide Detergents & soaps Heavy metals Aldehydes
  • 41. 1. Halogens Ionic (halide) or nonionic Mostly _______________ Germicidal and sporicidial with long exposure Affect protein structure (bonds)
  • 42. 1. Halogens Chlorine – Cl2, hypochlorites (chlorine bleach - OCl), chloramines – In water – release hypochlorous acid (HOCl) – Denaturation of proteins by disrupting disulfide bonds – Can be sporicidal – 0.6-1 ppm Cl2 to clean water – Bleach – sanitization/disinfection
  • 43. 1. Halogens Iodine - I2, iodophors (betadine) – Denature proteins – similar to Chlorine but not affected by organic matter or pH – Broad spectrum microbicide, can be sporicidal – Milder medical & dental degerming agents, disinfectants, ointments, topical antiseptic – Betadine (iodophor) = iodine + neutral polymer; allows for slow release and increased penetration – used as antiseptic
  • 44. 44
  • 45. 2. Phenolics Phenol ring (aromatic carbon ring) + groups Disrupt cell membranes & precipitate (denature) proteins; bactericidal, fungicidal, virucidal, not sporicidal – _______________ – ____________antibacterial additive to soaps – Mouthwash! (thymol) – Can be VERY toxic! Not typically used as antiseptics.
  • 46. _______________
  • 47. 3. _______________ Hibiclens, Hibitane A surfactant & protein denaturant with broad microbicidal properties Not sporicidal Used as skin _________ agents for preoperative scrubs, skin cleaning & burns
  • 48. 4. Alcohols Ethyl, isopropyl in solutions of 50-90% (water needed for protein coagulation) Act as surfactants dissolving membrane lipids and coagulating proteins of vegetative bacterial cells and fungi _______________ Isopropanol = rubbing alcohol, but vapors can be toxic
  • 49. 5. Hydrogen peroxide Weak (3%) to strong (25%) _______________ agent (steals electrons) Produce highly reactive hydroxyl free radicals that damage protein & DNA while also decomposing to O2 gas (bubbles) toxic to _______________ , overwhelms catalase in aerobes Strong solutions are sporicidal
  • 50. colonoscope
  • 51. 52
  • 52. 6. Detergents & soaps ________ compounds that work as _______________ Quaternary ammonia cpds (__________) act as surfactants that alter membrane permeability of some bacteria & fungi – Not sporicidal, ineffective against TB, hepatitis, pseudomonas Soaps- mechanically remove soil and grease containing microbes
  • 53. Figure 11.17 55
  • 54. 56
  • 55. 7. Heavy metals Solutions of silver & mercury kill vegetative cells in low concentrations by inactivating proteins Metallic salts Oligodynamic action Not sporicidal _________ to humans – Not used on broken skin
  • 56. 59
  • 57. 8. Aldehydes Glutaraldehyde & formaldehyde kill by alkylating protein & DNA (-CHO is reducing group) _______________ = H on AA is replaced by the aldehyde (and crosslinked) _______________ in 2% solution (Cidex) used as sterilant for heat sensitive instruments _______________ - disinfectant, preservative, toxicity limits use (formalin is aqueous solution)
  • 58. Gases & aerosols _______________, propylene oxide, betapropiolactone & chlorine dioxide Strong _______________ agents, sporicidal (sterilization)
  • 59. ________________________ – uses ethylene oxide
  • 60. 65
  • 61. Miscellaneous antimicrobials Dyes – crystal violet, acriflavine Acids, bases (alkalies) – destroy but some are corrosive and hazardous – Pickling – acetic acid – Sauerkraut, olives – lactic acid – Benzoic, sorbic acid – in lots of processed foods (preservatives = _______________ )