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MicrobialControlpart1
The document discusses microbial control through various physical and chemical methods. It begins with a brief history of bubonic plague in Europe during the Middle Ages caused by the Yersinia pestis bacterium. It then defines key terms like sterilization, disinfection, bactericidal and bacteriostatic. The document outlines several conditions that influence the effectiveness of antimicrobial agents and describes various physical methods of microbial control including heat, filtration and radiation. It provides details on how these methods kill microbes and examples of their applications.
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MicrobialControlpart1
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- 2. Outline • History • Definition of terms • Pattern of microbial death • Antimicrobial agents – Physical – Chemical
- 3. History Ring- a -ring of rosies Pocketful of posies Atichoo ! Atichoo ! We all fall down
- 4. Bubonic Plague orthe 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. Yersinia pestis -Gram (-) bacillus Vectors - Rat and Flea
- 6. Bubonic Plague Infection 1.Flea bite with Yersinia pestis 2. Bacteria multiply in the bloodstream Bacteremia 3. Bacteria localize in lymph nodes, especially axillary and groin areas
- 7. 4. Hemorrhaging occursin lymph nodes, resulting in reddish rash that will eventually become “black and blue” swellings or Buboes (hence the name Bubonic Plague or Black Death)
- 8. Bubonic Plague Infection 5.If untreated, about 50 % Mortality Rate 6. If bacteria spread to the lungs, it becomes Pneumonic Plague and is now highly contagious (Almost a 99 % Mortality Rate)
- 9. History Ring- a - ring of rosies Pocketful of posies Atichoo ! Atichoo ! We all fall down A pouch of sweet smelling herbs or posies were carried due to the belief that the disease was transmitted by bad smells
- 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. Smallpox Variola virus Eradicated in 1977 (Somalia)
- 12. Terms : Sterilization vs.Disinfection • Sterilization – destroying all forms of life • Disinfection – destroying pathogens or unwanted organisms
- 13. Disinfectant vs. Antiseptic • Disinfectant – antimicrobial agent used on inanimate objects • Antiseptic – antimicrobial agent used on living tissue
- 14. cidal vs. static • Bactericidal - kills bacteria • Bacteristatic - inhibits bacterial growth • Fungicidal • Fungistatic • Algacidal • Algastatic
- 15. — Commercial Sterilization: Killing C. botulinum endospores
- 16. Microbial death “a microbeis 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. “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. Conditions Influencing Effectiveness of Antimicrobial Agent Activity 1. Population size – Larger population requires a longer time to die 2. Population composition – Microorganisms vary markedly on susceptibility – Vegetative versus Spores – Young versus Mature cells 5. 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)
- 20. 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
- 22. Targets of AntimicrobialAgents 1. Cell membrane 2. Enzymes & Proteins 3. DNA & RNA
- 23. Methods of microbialcontrol • Physical – Heat – Filtration – Radiation • Chemical
- 24. HEAT • Flaming • Incineration • Hot-air sterilization • Moist-air sterilization Hot-air Autoclave Equivalent treatments 170˚C, 2 hr 121˚C, 15 min
- 25. HOW DOES HEATKILL 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
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- 27. • Thermal DeathPoint (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
- 28. • Decimal ReductionTime 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 temperatures However, such a destruction is logarithmic and it is theoretically NOT POSSIBLE to “completely destroy” microbes in a sample
- 29. 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
- 31. APPLICATION: After afood have been canned, it must be heated to eliminate the risk of botulism arising from the presence of Clostridium spores Example: IF the D value = 0.204 minutes It would take 12D or 2.5 minutes to reduce the spore number by heating at the specified temperature
- 32. APPLICATION: • If thez 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
- 33. THE USE OFPHYSICAL METHODS: 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
- 35. THE USE OFPHYSICAL 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