7 control of microbial growth


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7 control of microbial growth

  1. 1. <ul><li>Control of Microbial Growth </li></ul>Chapter 7
  2. 2. Terminology <ul><li>Sepsis refers to microbial contamination. </li></ul><ul><li>Asepsis is the absence of significant contamination. </li></ul><ul><li>Antisepsis: Removal of pathogens from living tissue </li></ul><ul><li>Degerming: Removal of microbes from a limited area </li></ul><ul><li>Sanitization: Lower microbial counts on eating utensils </li></ul>
  3. 3. Terminology cont’d <ul><li>Decontaminated </li></ul><ul><li>- item that has been treated to reduce # of disease causing organisms </li></ul><ul><li>Preservation </li></ul><ul><li>- delaying spoilage of foods </li></ul><ul><li>Sterilization, Disinfection, Antiseptic, Bacteriocidal, Bacteriostatic </li></ul>
  4. 4. Terms used: <ul><li>Sterilization vs. Disinfection </li></ul><ul><li>Sterilization: destroying all forms of life </li></ul><ul><li>Disinfection: destroying pathogens or unwanted organisms </li></ul><ul><li>Disinfectant vs. Antiseptic </li></ul><ul><li>Disinfectant: antimicrobial agent used on inanimate objects </li></ul><ul><li>Antiseptic : antimicrobial agent used on living tissue </li></ul>
  5. 6. cidal vs. static <ul><li>Biocide/Germicide: Kills microbes </li></ul><ul><li>Bacteriostasis: Inhibiting, not killing, microbes </li></ul><ul><li>Examples: </li></ul><ul><li>- Bactericidal - kills bacteria </li></ul><ul><li>- Bacteriostasis (Bacteriostatic)- inhibits bacterial growth </li></ul><ul><li>- Fungicidal </li></ul><ul><li>- Fungistatic </li></ul><ul><li>- Algacidal </li></ul><ul><li>- Algastatic </li></ul>
  6. 7. Methods of control <ul><li>Physical or chemical? </li></ul><ul><ul><li>physical control includes heat, irradiation, filtration and mechanical removal </li></ul></ul><ul><ul><li>Chemical control involves the use of microbial chemicals </li></ul></ul><ul><ul><li>Depends on the situation </li></ul></ul><ul><ul><li>degree of control required </li></ul></ul>
  7. 8. Methods of control cont’d <ul><li>Daily life </li></ul><ul><li>- Cooking </li></ul><ul><li>- refrigeration </li></ul><ul><li>- cleaning </li></ul><ul><li>- soap water </li></ul>mechanical Mechanical and chemical
  8. 9. <ul><li>Hospitals </li></ul><ul><ul><li>Important to minimize nosocomial infection (hospital acquired infection) due to </li></ul></ul><ul><ul><li>- weakened patients’ condition </li></ul></ul><ul><ul><li>- breaching of intact skin </li></ul></ul><ul><ul><li>- high concentration of pathogens from patients and workers </li></ul></ul><ul><ul><li>Sterile condition </li></ul></ul>Methods of control cont’d
  9. 10. <ul><li>Microbiology lab utilizes </li></ul><ul><ul><li>Sterile equipment </li></ul></ul><ul><ul><li>Aseptic technique </li></ul></ul><ul><ul><li>And possesses workers who takes care of the nature of of microbiologists (GLP) </li></ul></ul>Methods of control cont’d
  10. 11. <ul><li>Foods/food production industry </li></ul><ul><li>- physical removal </li></ul><ul><li>- adding chemicals </li></ul><ul><li>- may result in toxicity </li></ul><ul><li>- clean surface/ machinery </li></ul>Methods of control cont’d
  11. 12. Selection of Control Method <ul><li>Antimicrobial procedure used for control of microbial growth is based on </li></ul><ul><ul><li>Types of microbe </li></ul></ul><ul><ul><li>Extent of contamination </li></ul></ul><ul><ul><li>Environmental conditions </li></ul></ul><ul><ul><li>Potential risk </li></ul></ul>
  12. 13. Selection of Control Method cont’d <ul><li>Types of microorganism </li></ul><ul><li>- some organisms are more resistant and require stronger measures for control </li></ul><ul><li>- endospores require chemical treatment for 10 hours </li></ul><ul><li>- Mycobacterium ’s waxy cells are resistant to chemicals </li></ul>Mycobacterial cell wall: 1-outer lipids, 2-mycolic acid, 3-polysaccharides (arabinogalactan), 4-peptidoglycan, 5-plasma membrane, 6-lipoarabinomannan (LAM), 7-phosphatidylinositol mannoside, 8-cell wall skeleton
  13. 14. <ul><li>Extent of microbial population </li></ul><ul><li>- larger population take more time to destroy </li></ul><ul><li>- usually 90% of the population is destroyed in </li></ul><ul><li>a given period </li></ul><ul><li>e.g if in 1 st 3 minutes 90% of the population is destroyed, then 90% of the remaining population gets destroyed in the next 3 minutes and so on </li></ul>Selection of Control Method cont’d
  14. 16. <ul><li>Environmental conditions </li></ul><ul><li>- pH, temperature </li></ul><ul><li>- presence of </li></ul><ul><li>- organics: blood </li></ul><ul><li>- dirt </li></ul><ul><li>- grease </li></ul><ul><li>- the potential risk of transmitting infectious agents </li></ul><ul><li>- critical items </li></ul><ul><li>- semicritical items </li></ul><ul><li>- non-critical items </li></ul>Selection of Control Method cont’d Must be cleaned first, then controlled
  15. 17. <ul><li>Critical items have </li></ul><ul><li>- indirect contact with body tissues </li></ul><ul><li>- needles, scalpels </li></ul><ul><li>Semicritical items have contact with </li></ul><ul><li>- mucous membranes but it does not penetrate </li></ul><ul><li>endoscopes, endotrachial tubes </li></ul>Selection of Control cont’d
  16. 18. Selection of Control cont’d <ul><li>Non-critical items have </li></ul><ul><li>- indirect contact with unbroken skin </li></ul><ul><li>- countertops, stethoscopes </li></ul>
  17. 19. Methods to Control Microbial Growth
  18. 20. Physical Microbial Controls: Heat <ul><li>Heat as a microbial control </li></ul><ul><li>- fast, reliable, inexpensive </li></ul><ul><li>- does not introduce potential toxic substances </li></ul><ul><li>Types of heat control include </li></ul><ul><li>- moist heat </li></ul><ul><li>- pasteurization </li></ul><ul><li>- pressurized steam </li></ul><ul><li>- dry heat </li></ul>
  19. 21. <ul><li>Moist heat </li></ul><ul><li>- causes irreversible coagulation of proteins found in microorganisms </li></ul><ul><li>- 10 minutes of boiling </li></ul><ul><li>- most microbes and viruses will be destroyed except endospores and few others which can survives hours of boiling </li></ul>Physical Microbial Controls: Heat cont’d
  20. 22. <ul><li>Pasteurization </li></ul><ul><li>- reduces number of heat sensitive organisms </li></ul><ul><li>- widely used in milk and juices </li></ul><ul><li>increases shelf life and does not alter quality </li></ul><ul><li>- original pasteurization was 62ºC, 30 mins </li></ul><ul><li>- now: UHT-shorter time 72ºC, 15 secs </li></ul>Physical Microbial Controls: Heat cont’d
  21. 23. <ul><li>Pressurized steam </li></ul><ul><li>- pressure cooker or autoclave </li></ul><ul><li>- higher air pressure increases the temperature </li></ul><ul><li>at which steam forms </li></ul><ul><li>- 15 psi (lbs/square inch) at 121ºC for 15 mins </li></ul><ul><li>-effective to kill endospores </li></ul>Physical Microbial Controls: Heat cont’d
  22. 24. The autoclave: Moist heat and pressure <ul><li>15psi, 121ºC, 15 minutes </li></ul><ul><li>Thermal death point (TDP) : Lowest temperature at which all cells in a culture get killed in 10 mins </li></ul><ul><li>Thermal death time (TDT): time to kill all cells in a culture </li></ul><ul><li>Decimal reduction time (DRT) : Minutes to kill 90% of a population at a given temperature </li></ul>
  23. 25. The autoclaving machine
  24. 26. Temperature of steam and Pressure at sea level
  25. 27. The autoclaving machine
  26. 28. <ul><li>Dry heat </li></ul><ul><li>- without moisture e.g. flaming </li></ul><ul><li>- burns cell constituents </li></ul><ul><li>- object is oxidized to ash </li></ul><ul><li>- irreversibly denatures proteins </li></ul><ul><li>- takes longer (200ºC, 1.5 hrs dry=121ºC, 15 min moist) </li></ul><ul><li>- advantages are for powders, does not corrode metals and blunt sharps </li></ul><ul><li>- e.g flasks, tubes, pipettes in microbiological laboratories. </li></ul>Physical Microbial Controls: Heat cont’d
  27. 29. Physical Microbial Controls: Filtration <ul><li>Used for heat sensitive fluids </li></ul><ul><li>air </li></ul>
  28. 30. <ul><li>Fluids </li></ul><ul><ul><li>solutions of antibiotics, vitamins, tissue extracts, animal serum, etc. </li></ul></ul><ul><ul><li>Depth filters </li></ul></ul><ul><ul><li>– able to retain microorganisms while allowing fluids to pass through </li></ul></ul><ul><ul><li>Membrane Filter </li></ul></ul><ul><ul><li>- The use of graded pore size 0.2-0.4µm </li></ul></ul>Physical Microbial Controls: Filtration cont’d
  29. 31. <ul><li>Air </li></ul><ul><ul><li>- HEPA (High Efficient Particulate Air) filter and laminar air flow are commonly used </li></ul></ul><ul><ul><li>- filter incoming air and outgoing air respectively </li></ul></ul><ul><ul><li>- HEPA filter prevents the income of 0.3µm and large size particles to enter. </li></ul></ul>Physical Microbial Controls: Filtration cont’d
  30. 32. <ul><li>“ Cold sterilization “ for disposable materials made up of plastics, wool, cotton, etc without altering the material. </li></ul><ul><li>Radiation damages DNA </li></ul><ul><li>Ionizing radiation (X-rays, gamma rays, electron beams) </li></ul><ul><li>Non-ionizing radiation </li></ul><ul><li>- UV </li></ul><ul><li>- Microwaves kill by heat not especially </li></ul><ul><li>antimicrobial </li></ul>Physical Microbial Controls: Radiation
  31. 34. <ul><li>Gamma irradiation </li></ul><ul><li>- penetrate deeply </li></ul><ul><li>- for heat sensitive materials </li></ul><ul><li>- causes biological damage to microorganisms </li></ul><ul><li>- does not alter food flavor (meat) </li></ul>Physical Microbial Controls: Radiation cont’d
  32. 35. <ul><li>UV light </li></ul><ul><ul><li>damages the structure and function of nucleic acids </li></ul></ul><ul><ul><li>Penetrate poorly- cannot penetrate even into liquid. </li></ul></ul><ul><ul><li>Used to disinfect surfaces </li></ul></ul><ul><ul><li>Can cause damage to human cells </li></ul></ul><ul><ul><li>Germicidal lamps -kill or reduce the number of viable microorganisms to sterilize microbiological laboratories hospital operating rooms, and specific filling rooms in various industries </li></ul></ul>Physical Microbial Controls: Radiation cont’d
  33. 36. <ul><li>Microwave </li></ul><ul><ul><li>Kills by heat </li></ul></ul><ul><ul><li>Does not affect microorganisms directly </li></ul></ul>Physical Microbial Controls: Radiation cont’d
  34. 37. Physical Methods used to control Microbial growth
  35. 42. Chemical Microbial Control
  36. 44. <ul><li>Grouped according to potency </li></ul><ul><ul><li>Sterilants </li></ul></ul><ul><ul><li>High-level </li></ul></ul><ul><ul><li>Intermediate level </li></ul></ul><ul><ul><li>Low level </li></ul></ul>Chemical Microbial Control cont’d
  37. 45. Chemical Control <ul><li>sterilants </li></ul><ul><li>destroy microorganisms, endospores and viruses </li></ul><ul><li>used for critical equipment-scalpels </li></ul>
  38. 46. chemical control cont'd <ul><li>high level </li></ul><ul><li>- destroy viruses and  vegetative microorganisms (no endospores) </li></ul><ul><li>- used for semicritical equipment: endoscopes </li></ul><ul><li>intermediate level </li></ul><ul><li>- destroy vegetative microorganisms, some viruses </li></ul><ul><li>- used for non-critical equipment: sthetoscopes </li></ul><ul><li>low level </li></ul><ul><li>-destroy fungi, vegetative microorganisms </li></ul><ul><li>- used for general purpose disinfectants </li></ul>
  39. 47. Selecting Germicidal Chemical <ul><li>Germicide: An agent capable of killing pathogens and non-pathogens but not necessarily endospores </li></ul><ul><li>toxicity to human or environment? </li></ul><ul><li>- weigh the benefits vs the risks </li></ul><ul><li>presence of organic material </li></ul><ul><li>- hypochlotrite is inactivated by the presence of organic matter </li></ul><ul><li>compatibility </li></ul><ul><li>-electrical equipment with a liquid?? </li></ul><ul><li>residue </li></ul><ul><li>- some have to be rinsed with sterile water </li></ul><ul><li>cost and availability </li></ul>
  40. 48. Selecting germicidal Chemical cont'd <ul><li>storage and stability </li></ul><ul><li>- may come in concentrated form for ease in storing </li></ul><ul><li>- those have to be mixed </li></ul><ul><li>environmental risk </li></ul><ul><li>- is neutralization necessary before disposal? </li></ul>
  41. 49. Classes of Germicidal Chemicals <ul><li>alcohols alcohols </li></ul><ul><li>aldehydes </li></ul><ul><li>biguanides </li></ul><ul><li>ethylene oxide  </li></ul><ul><li>halogens: oxidize proteins </li></ul>
  42. 50. Classes of Germicidal Chemicals <ul><li>alcohols </li></ul><ul><li>- coagulated enzymes and proteins </li></ul><ul><li>- damage lipid membranes </li></ul><ul><li>- on-toxic </li></ul><ul><li>- inexpensive </li></ul><ul><li>- no residue </li></ul>
  43. 51. Classes of Germicidal Chemicals cont’d <ul><li>aldehydes </li></ul><ul><li>- inactivate proteins and nucleic acids </li></ul><ul><li>- toxic to humans </li></ul><ul><li>Peroxygens </li></ul><ul><li>- oxidizing agents </li></ul><ul><li>- hydrogen peroxide </li></ul><ul><li>- leaves no residue </li></ul>
  44. 52. Classes of Germicidal Chemicals cont’d <ul><li>biguanides </li></ul><ul><li>- extensive antiseptic use </li></ul><ul><li>- adheres and persists on skin, mucous membranes </li></ul><ul><li>- low toxicity </li></ul><ul><li>Phenolic compounds </li></ul><ul><ul><li>Hitorically important </li></ul></ul><ul><ul><li>Irritant, unpleasant odor </li></ul></ul><ul><ul><li>Destroy cytoplasmic membrane and denatures protein </li></ul></ul>
  45. 53. Classes of Germicidal Chemicals cont’d <ul><li>ethylene oxide  </li></ul><ul><li>- reacts with proteins </li></ul><ul><li>- gas: penetrable  </li></ul><ul><li>- mutagenic </li></ul><ul><li>Metal compounds </li></ul><ul><ul><li>Interfere protein function </li></ul></ul><ul><ul><li>Toxic </li></ul></ul><ul><ul><li>pollutants </li></ul></ul>
  46. 54. Classes of Germicidal Chemicals cont’d <ul><li>halogens: oxidize proteins </li></ul><ul><li>-chlorine </li></ul><ul><li>-irritating to skin </li></ul><ul><li>-organic compounds consume free chlorine </li></ul><ul><li>-iodine </li></ul><ul><li>-tincture </li></ul><ul><li>- Iodophore </li></ul>
  47. 55. Effect of germicidal activity on Microbes
  48. 56. Effect of germicidal activity on Microbes
  49. 57. Chemical methods of microbial control <ul><li>Evaluating a disinfectant </li></ul><ul><li>- Disk diffusion method </li></ul>
  50. 58. Preservation of Perishables <ul><li>Extends shelf life </li></ul><ul><ul><li>Slow or halts microbial growth thus delaying spoilage </li></ul></ul>
  51. 59. <ul><li>Chemical preservatives </li></ul><ul><ul><li>Some chemical preservatives are used in non-food items </li></ul></ul><ul><ul><li>Food preservatives must be non-toxic to humans </li></ul></ul><ul><ul><ul><li>Benzoic acid, propionic acids, nitrate are commonly used </li></ul></ul></ul><ul><ul><ul><li>Nitrate </li></ul></ul></ul><ul><ul><ul><ul><li>Inhibits germination of C. botulinum endospores </li></ul></ul></ul></ul>Preservation of Perishables
  52. 60. Preservation of Perishables <ul><li>Low temperature storage </li></ul><ul><ul><li>Temperature dependent </li></ul></ul><ul><ul><ul><li>most microorganisms do not reproduce in ordinary refrigerator (0-7ºC) </li></ul></ul></ul><ul><ul><li>Freezing </li></ul></ul><ul><ul><ul><li>ice crystals can cause irreversible damage to many microorganisms (kills up to 50% growth) </li></ul></ul></ul><ul><ul><ul><li>Freezing stops all growth, but may start to reproduce again once food is thawed </li></ul></ul></ul>
  53. 61. <ul><li>Reducing water </li></ul><ul><ul><li>Salt/sugar </li></ul></ul><ul><ul><li>Draw water out of cell </li></ul></ul><ul><ul><li>Less available for microorganisms </li></ul></ul><ul><li>Drying </li></ul><ul><ul><li>Desiccation </li></ul></ul><ul><ul><ul><li>Removing water such as milk powder </li></ul></ul></ul>Preservation of Perishables Salt cured meat
  54. 62. <ul><li>Lyophilization </li></ul><ul><ul><li>Freeze drying </li></ul></ul><ul><ul><ul><li>Freeze food first </li></ul></ul></ul><ul><ul><ul><li>followed by putting in vacuum </li></ul></ul></ul>Preservation of Perishables
  55. 63. Factors that influence effectiveness <ul><li>Number of microbes </li></ul><ul><li>Environmental influences </li></ul><ul><li>Time of exposure </li></ul><ul><li>Microbial characteristics </li></ul>
  56. 64. Microbial death curve
  57. 65. Limitations: Microbial Characteristics
  58. 66. Actions of Microbial Control Agents <ul><li>Alteration of membrane permeability </li></ul><ul><li>Damage to proteins </li></ul><ul><li>Damage to nucleic acids </li></ul>
  59. 67. Questions???? Sand rich in salts n nitrates preserved mummy