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for bio120lec1 2nd sem AY 2011-2012 UPM

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  1. 1. Microbial Control
  2. 2. Outline•  History•  Definition of terms•  Pattern of microbial death•  Antimicrobial agents –  Physical –  Chemical
  3. 3. HistoryRing- a - ring of rosies Pocketful of posies Atichoo ! Atichoo ! We all fall down
  4. 4. Bubonic Plague or the Black Death•  Epidemic swept thru Europe in the Middle Ages (13th and 14th centuries)•  40 million people were killed –  About 1/3 of the population of the continent•  Etiological agent: –  Yersinia pestis Gram (-) rod•  2 Vectors –  Rat –  Flea
  5. 5. Yersinia pestis - Gram (-) bacillusVectors - Rat and Flea
  6. 6. Bubonic Plague Infection1. Flea bite with Yersinia pestis2. Bacteria multiply in the bloodstream Bacteremia3. Bacteria localize in lymph nodes,especially axillary and groin areas
  7. 7. 4. Hemorrhaging occurs in lymph nodes,resulting in reddish rash that will eventuallybecome “black and blue” swellings or Buboes(hence the name Bubonic Plague or BlackDeath)
  8. 8. Bubonic Plague Infection5. If untreated, about 50 % Mortality Rate6. If bacteria spread to the lungs, it becomesPneumonic Plague and is now highlycontagious (Almost a 99 % Mortality Rate)
  9. 9. History Ring- a - ring of rosies Pocketful of posies Atichoo ! Atichoo ! We all fall downA pouch of sweet smelling herbs or posies were carried due tothe belief that the disease was transmitted by bad smells
  10. 10. Humans vs. Microbes•  Most of History, microbes have been winning the battle•  In the last 100 yrs or so the battle has swung in our favor –  Why? •  Because of our increasing knowledge of how to Control Microbial Growth
  11. 11. Smallpox Variola virusEradicated in 1977 (Somalia)
  12. 12. Terms :Sterilization vs. Disinfection•  Sterilization –  destroying all forms of life•  Disinfection –  destroying pathogens or unwanted organisms
  13. 13. Disinfectant vs. Antiseptic•  Disinfectant –  antimicrobial agent used on inanimate objects•  Antiseptic –  antimicrobial agent used on living tissue
  14. 14. cidal vs. static•  Bactericidal - kills bacteria•  Bacteristatic - inhibits bacterial growth•  Fungicidal•  Fungistatic•  Algacidal•  Algastatic
  15. 15. —  Commercial Sterilization: Killing C. botulinum endospores
  16. 16. Microbial death“a microbe is defined DEAD if it does not grow when inoculated into culture medium that would normally support its growth”Death is defined as the inability of the organisms to form a visible colony –James Jay (Modern Food Microbiology 6th ed)
  17. 17. “It takes more time to kill a large population of bacteria than it does to kill a small population, because only a fraction of organisms die during a given time interval.Bacterial populations die at a constant logarithmic rate
  18. 18. Conditions Influencing Effectiveness of Antimicrobial Agent Activity1.  Population size –  Larger population requires a longer time to die2.  Population composition –  Microorganisms vary markedly on susceptibility –  Vegetative versus Spores –  Young versus Mature cells5.  Concentration or Intensity of an Antimicrobial Agent –  The more concentrated an agent the more rapidly microbes can be destroyed –  BUT sometimes an agent may be more effective at lower concentrations (e.g. 70% alcohol)
  19. 19. Conditions Influencing Effectiveness of Antimicrobial Agent Activity 3.  Duration of Exposure –  The longer the exposure to an agent the more they will be killed 6.  Temperature –  An increase in temperature at which a chemical acts often enhances it activity –  Example: acids used in high T = more effective 7.  Local environment –  pH, organic matter, etc –  Controls or Protects the pathogen
  20. 20. Targets of Antimicrobial Agents1. Cell membrane2. Enzymes & Proteins3. DNA & RNA
  21. 21. Methods of microbial control•  Physical –  Heat –  Filtration –  Radiation•  Chemical
  22. 22. HEAT•  Flaming•  Incineration•  Hot-air sterilization•  Moist-air sterilization Hot-air AutoclaveEquivalent treatments 170˚C, 2 hr 121˚C, 15 min
  23. 23. HOW DOES HEAT KILL MICROBES•  MOIST HEAT –  Kill effectively by degrading nucleic acids and by denaturing enzymes and other essential proteins –  May also disrupt cell membranes•  DRY HEAT –  Microbial death results from the oxidation of cell constituents and denaturation of proteins
  25. 25. •  Thermal Death Point (TDP) –  The lowest temperature at which a microbial suspension in killed in 10 minutes•  Thermal Death Time (TDT) –  The shortest time needed to kill all organisms in a microbial suspension at a specific temperature and under defined conditions
  26. 26. •  Decimal Reduction Time or D value –  Time required to kill 90% of the microorganisms or spores in a sample at a specified temperature –  Time required for the line to drop by one log cycle or tenfold –  Used to estimate the relative resistance of a microbe to different temperaturesHowever, such a destruction is logarithmic and it is theoreticallyNOT POSSIBLE to “completely destroy” microbes in a sample
  27. 27. The z Value and The F Value•  z Value –  The increase in temperature required to reduce D to 1/10 its value or to reduce it by one log cycle•  F value –  Time in minutes at a specific temperature needed to kill a population of cells or spores –  Usually 121°C
  28. 28. APPLICATION: After a food have been canned, it must be heated toeliminate the risk of botulism arising from the presence of Clostridium sporesExample:IF the D value = 0.204 minutesIt would take 12D or 2.5 minutes toreduce the spore number by heating atthe specified temperature
  29. 29. APPLICATION:•  If the z value for Clostridium spores is 10°C•  It takes a 10°C change in temperature to alter the D value tenfold•  THUS: if the cans are to be processed at 111°C rather than 121°C, the D value would increase by tenfold t 2.04 minutes•  The 12D value = 24.5 minutes
  30. 30. THE USE OF PHYSICALMETHODS: FILTRATION•  Applicable for heat-sensitive materials that needs sterilization•  2 types of filters –  Depth filters: consist of fibrous or granular materials that have been bonded into a thick layer filled with twisting channels of small diameter –  Membrane filters: porous membranes; 0.2 µm pore sizes•  Laminar flow hood versus biological safety cabinets (HEPA filters) –  High Efficiency Particulate Air –  Remove 99.97% particles –  for sterilizing AIR
  31. 31. THE USE OF PHYSICAL METHODS: RADIATION•  IONIZING RADIATION •  X rays, gamma rays, electron beams •  Excellent as a sterilizing agent and penetrates deep into objects•  NON-IONIZING RADIATION –  UV (about 260nm) –  Quite lethal but does not penetrate glass, dirt films, water and other substances very effectively•  Microwaves: kill by heat not usually antimicrobial