Ch 07_lecture_presentation

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Ch 07_lecture_presentation

  1. 1. Chapter 7 The Control of Microbial Growth © 2013 Pearson Education, Inc. Copyright © 2013 Pearson Education, Inc. Lectures prepared by Christine L. Case Lectures prepared by Christine L. Case
  2. 2. © 2013 Pearson Education, Inc.
  3. 3. The Terminology of Microbial Control Learning Objective 7-1 Define the following key terms related to microbial control: sterilization, disinfection, antisepsis, degerming, sanitization, biocide, germicide, bacteriostasis, and asepsis. © 2013 Pearson Education, Inc.
  4. 4. The Terminology of Microbial Control  Sepsis refers to microbial contamination  Asepsis is the absence of significant contamination  Aseptic surgery techniques prevent microbial contamination of wounds © 2013 Pearson Education, Inc.
  5. 5. The Terminology of Microbial Control  Sterilization: removing all microbial life  Commercial sterilization: killing C. botulinum endospores  Disinfection: removing pathogens  Antisepsis: removing pathogens from living tissue © 2013 Pearson Education, Inc.
  6. 6. The Terminology of Microbial Control  Degerming: removing microbes from a limited area  Sanitization: lowering microbial counts on eating utensils  Biocide/germicide: killing microbes  Bacteriostasis: inhibiting, not killing, microbes © 2013 Pearson Education, Inc.
  7. 7. Check Your Understanding  The usual definition of sterilization is the removal or destruction of all forms of microbial life; how could there be practical exceptions to this simple definition? 7-1 © 2013 Pearson Education, Inc.
  8. 8. The Rate of Microbial Death Learning Objective 7-2 Describe the patterns of microbial death caused by treatments with microbial control agents. © 2013 Pearson Education, Inc.
  9. 9. Table 7.2 Microbial Exponential Death Rate: An Example © 2013 Pearson Education, Inc.
  10. 10. Figure 7.1a Understanding the Microbial Death Curve. One log decrease = 90% of population killed Arithmetic number of surviving cells log10 of number of surviving cells Plotting the typical microbial death curve logarithmically (red line) results in a straight line. Time (min) (a) Plotting the typical microbial death curve arithmetically (blue line) is impractical: at 3 minutes the population of 1000 cells would only be a hundredth of the graphed distance between 100,000 and the baseline. © 2013 Pearson Education, Inc.
  11. 11. Effectiveness of Treatment  Depends on:     Number of microbes Environment (organic matter, temperature, biofilms) Time of exposure Microbial characteristics © 2013 Pearson Education, Inc.
  12. 12. Figure 7.1b Understanding the Microbial Death Curve. log10 of number of surviving cells sterile surgical equipment H Lo w po pu l ig h at io n po pu la tio n lo ad lo ad Time (min) (b) Logarithmic plotting (red) reveals that if the rate of killing is the same, it will take longer to kill all members of a larger population than a smaller one, whether using heat or chemical treatments. © 2013 Pearson Education, Inc.
  13. 13. Check Your Understanding  How is it possible that a solution containing a million bacteria would take longer to sterilize than one containing a half-million bacteria? 7-2 © 2013 Pearson Education, Inc.
  14. 14. Actions of Microbial Control Agents Learning Objective 7-3 Describe the effects of microbial control agents on cellular structures. © 2013 Pearson Education, Inc.
  15. 15. Actions of Microbial Control Agents  Alteration of membrane permeability  Damage to proteins  Damage to nucleic acids © 2013 Pearson Education, Inc.
  16. 16. Check Your Understanding  Would a chemical microbial control agent that affects plasma membranes affect humans? 7-3 © 2013 Pearson Education, Inc.
  17. 17. Physical Methods of Microbial Control Learning Objectives 7-4 Compare the effectiveness of moist heat (boiling, autoclaving, pasteurization) and dry heat. 7-5 Describe how filtration, low temperatures, high pressure, desiccation, and osmotic pressure suppress microbial growth. 7-6 Explain how radiation kills cells. © 2013 Pearson Education, Inc.
  18. 18. Heat  Thermal death point (TDP): lowest temperature at which all cells in a culture are killed in 10 min  Thermal death time (TDT): time during which all cells in a culture are killed © 2013 Pearson Education, Inc.
  19. 19. Decimal Reduction Time (DRT)  Minutes to kill 90% of a population at a given temperature © 2013 Pearson Education, Inc.
  20. 20. Figure 7.10 A comparison of the effectiveness of various antiseptics. © 2013 Pearson Education, Inc.
  21. 21. Moist Heat Sterilization  Moist heat denatures proteins  Autoclave: steam under pressure © 2013 Pearson Education, Inc.
  22. 22. Figure 7.2 An autoclave. Exhaust valve (removes steam after sterilization) Steam to chamber Safety valve Pressure gauge Operating valve (controls steam from jacket to chamber) Steam Door Steam chamber Air Perforated shelf Steam jacket Sediment screen Thermometer Automatic ejector valve Pressure regulator (thermostatically controlled; for steam supply closes on contact with pure steam when air is To waste line exhausted) Steam supply © 2013 Pearson Education, Inc.
  23. 23. Steam Sterilization  Steam must contact item’s surface © 2013 Pearson Education, Inc.
  24. 24. Figure 7.3 Examples of sterilization indicators. © 2013 Pearson Education, Inc.
  25. 25. Pasteurization  Reduces spoilage organisms and pathogens  Equivalent treatments     63°C for 30 min High-temperature short-time: 72°C for 15 sec Ultra-high-temperature: 140°C for <1 sec Thermoduric organisms survive © 2013 Pearson Education, Inc.
  26. 26. Dry Heat Sterilization  Kills by oxidation     Dry heat Flaming Incineration Hot-air sterilization Hot-Air Equivalent Treatments © 2013 Pearson Education, Inc. Autoclave 170˚C, 2 hr 121˚C, 15 min
  27. 27. Filtration  HEPA removes microbes >0.3 µm  Membrane filtration removes microbes >0.22 µm © 2013 Pearson Education, Inc.
  28. 28. Figure 7.4 Filter sterilization with a disposable, presterilized plastic unit. Flask of sample Cap Membrane filter Cotton plug in vacuum line ensures sterility Sterile filtrate © 2013 Pearson Education, Inc. Vacuum line
  29. 29. Physical Methods of Microbial Control  Low temperature inhibits microbial growth  Refrigeration  Deep-freezing  Lyophilization  High pressure denatures proteins  Desiccation prevents metabolism  Osmotic pressure causes plasmolysis © 2013 Pearson Education, Inc.
  30. 30. Figure 7.5 The radiant energy spectrum. © 2013 Pearson Education, Inc.
  31. 31. Radiation  Ionizing radiation (X rays, gamma rays, electron beams)  Ionizes water to release OH•  Damages DNA  Nonionizing radiation (UV, 260 nm)  Damages DNA  Microwaves kill by heat; not especially antimicrobial © 2013 Pearson Education, Inc.
  32. 32. Check Your Understanding  How is microbial growth in canned foods prevented? 7-4  Why would a can of pork take longer to sterilize at a given temperature than a can of soup that also contained pieces of pork? 7-5  What is the connection between the killing effect of radiation and hydroxyl radical forms of oxygen? 7-6 © 2013 Pearson Education, Inc.
  33. 33. Chemical Methods of Microbial Control Learning Objectives 7-7 List the factors related to effective disinfection. 7-8 Interpret the results of use-dilution tests and the disk-diffusion method. © 2013 Pearson Education, Inc.
  34. 34. Principles of Effective Disinfection     Concentration of disinfectant Organic matter pH Time © 2013 Pearson Education, Inc.
  35. 35. Use-Dilution Test  Metal rings dipped in test bacteria are dried  Dried cultures are placed in disinfectant for 10 min at 20°C  Rings are transferred to culture media to determine whether bacteria survived treatment © 2013 Pearson Education, Inc.
  36. 36. Figure 7.6 Evaluation of disinfectants by the disk-diffusion method. Zone of inhibition Chlorine O-phenylphenol Hexachlorophene Quat Staphylococcus aureus (gram-positive) © 2013 Pearson Education, Inc. Chlorine O-phenylphenol Hexachlorophene Quat Escherichia coli (gram-negative) Chlorine O-phenylphenol Hexachlorophene Quat Pseudomonas aeruginosa (gram-negative)
  37. 37. Clinical Focus  Which preparation is more effective? © 2013 Pearson Education, Inc.
  38. 38. Clinical Focus 7.1 Infection Following Steroid Injection Undiluted Disk-diffusion test of Zephiran against M. abscessus. © 2013 Pearson Education, Inc. 1:10
  39. 39. Check Your Understanding  If you wanted to disinfect a surface contaminated by vomit and a surface contaminated by a sneeze, why would your choice of disinfectant make a difference? 7-7  Which is more likely to be used in a medical clinic laboratory, a use-dilution test or a disk-diffusion test? 7-8 © 2013 Pearson Education, Inc.
  40. 40. Chemical Methods of Microbial Control Learning Objectives 7-9 Identify the methods of action and preferred uses of chemical disinfectants. 7-10 Differentiate halogens used as antiseptics from halogens used as disinfectants. 7-11 Identify the appropriate uses for surface-active agents. 7-12 List the advantages of glutaraldehyde over other chemical disinfectants. 7-13 Identify chemical sterilizers. © 2013 Pearson Education, Inc.
  41. 41. Phenol and Phenolics  Disrupt plasma membranes © 2013 Pearson Education, Inc.
  42. 42. Figure 7.7ab The structure of phenolics and bisphenols. (a) Phenol © 2013 Pearson Education, Inc. (b) O-phenylphenol
  43. 43. Bisphenols  Hexachlorophene, triclosan  Disrupt plasma membranes © 2013 Pearson Education, Inc.
  44. 44. Figure 7.7cd The structure of phenolics and bisphenols. (c) Hexachlorophene (a bisphenol) (d) Triclosan (a bisphenol) © 2013 Pearson Education, Inc.
  45. 45. Biguanides  Chlorhexidine  Disrupts plasma membranes © 2013 Pearson Education, Inc.
  46. 46. Halogens  Iodine  Tinctures: in aqueous alcohol  Iodophors: in organic molecules  Alter protein synthesis and membranes  Chlorine  Bleach: hypochlorous acid (HOCl)  Chloramine: chlorine + ammonia  Oxidizing agents © 2013 Pearson Education, Inc.
  47. 47. Alcohols  Ethanol, isopropanol  Denature proteins, dissolve lipids  Require water © 2013 Pearson Education, Inc.
  48. 48. Table 7.6 Biocidal Action of Various Concentrations of Ethanol in Aqueous Solution against Streptococcus pyogenes © 2013 Pearson Education, Inc.
  49. 49. Heavy Metals  Ag, Hg, and Cu  Silver nitrate may be used to prevent gonorrheal ophthalmia neonatorum  Silver sulfadiazine used as a topical cream on burns  Copper sulfate is an algicide  Oligodynamic action  Denature proteins © 2013 Pearson Education, Inc.
  50. 50. Figure 7.8 Oligodynamic action of heavy metals. © 2013 Pearson Education, Inc.
  51. 51. Figure 7.9 The ammonium ion and a quaternary ammonium compound, benzalkonium chloride (Zephiran). Ammonium ion © 2013 Pearson Education, Inc. Benzalkonium chloride
  52. 52. Surface-Active Agents, or Surfactants Soap Degerming Acid-anionic detergents Sanitizing Quaternary ammonium compounds (cationic detergents) Bactericidal, denature proteins, disrupt plasma membrane © 2013 Pearson Education, Inc.
  53. 53. Chemical Food Preservatives  Organic acids  Inhibit metabolism  Sorbic acid, benzoic acid, and calcium propionate  Control molds and bacteria in foods and cosmetics  Nitrite prevents endospore germination  Antibiotics  Nisin and natamycin prevent spoilage of cheese © 2013 Pearson Education, Inc.
  54. 54. Aldehydes  Inactivate proteins by cross-linking with functional groups (–NH2, –OH, –COOH, –SH)  Use: medical equipment  Glutaraldehyde, formaldehyde, and ortho-phthalaldehyde © 2013 Pearson Education, Inc.
  55. 55. Gaseous Sterilants  Denature proteins  Use: heat-sensitive material  Ethylene oxide © 2013 Pearson Education, Inc.
  56. 56. Plasma  Free radicals destroy microbes  Use: tubular instruments © 2013 Pearson Education, Inc.
  57. 57. Supercritical Fluids  CO2 with gaseous and liquid properties  Use: medical implants © 2013 Pearson Education, Inc.
  58. 58. Peroxygens  Oxidizing agents  Use: contaminated surfaces  O3, H2O2, peracetic acid © 2013 Pearson Education, Inc.
  59. 59. Check Your Understanding  Why is alcohol effective against some viruses and not others? 7-9  Is Betadine an antiseptic or a disinfectant when it is used on skin? 7-10  What characteristics make surface-active agents attractive to the dairy industry? 7-11  What chemical disinfectants can be considered sporicides? 7-12  What chemicals are used to sterilize? 7-13 © 2013 Pearson Education, Inc.
  60. 60. Microbial Characteristics and Microbial Control Learning Objective 7-14 Explain how the type of microbe affects the control of microbial growth. © 2013 Pearson Education, Inc.
  61. 61. Figure 7.11 Decreasing order of resistance of microorganisms to chemical biocides. © 2013 Pearson Education, Inc.
  62. 62. Table 7.7 The Effectiveness of Chemical Antimicrobials against Endospores and Mycobacteria © 2013 Pearson Education, Inc.
  63. 63. Check Your Understanding  The presence or absence of endospores has an obvious effect on microbial control, but why are gram-negative bacteria more resistant to chemical biocides than gram-positive bacteria? 7-14 © 2013 Pearson Education, Inc.

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