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Physical and Chemical Control of Microorganisms

Physical and Chemical Control of Microorganisms. I. Terms II. Factors which determine the effectiveness of control methods III. Methods of physical control IV. Chemical agents. Terms. 1) “ Control ” -- Limiting exposure to _______________________ agents

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Physical and Chemical Control of Microorganisms

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  1. Physical and Chemical Control of Microorganisms • I. Terms • II. Factors which determine the effectiveness of control methods • III. Methods of physical control • IV. Chemical agents

  2. Terms • 1) “Control” -- Limiting exposure to _______________________ agents • Microorganisms are part of our environment • Infection can be controlled by limiting exposure to infectious agents • 2) _______________ -- Removal or destruction of all _________________ microorganisms. “sterile” • 3)Disinfection -- Removal or destruction of pathogens from ________________________ areas. “disinfectant” • 4) Antisepsis -- Removal or destruction of vegetative forms from _______ _____________. “antiseptic” Note: Antiseptics and disinfectants do the same thing, but in different environments

  3. Terms (continued) • 5) Sanitization -- any cleansing technique that mechanically removes microorganisms. Usually soaps

  4. More terms • 7) “-static” means ‘to stand still’. Refers to an agent which prevents _______________ but doesn’t kill. • “Bacteriostatic” or “fungistatic” or “virustatic” agent • 6) “-cide” refers to ______________. • “Bacteriocide” kills bacteria, “fungicide” kills fungi, etc.

  5. Factors which determine the effectiveness of a control method • 1. The number of microorganisms “Death curve” 107 106 # of ________ cells 105 104 Note log scale on y axis (each increment is 10X reduction in numbers) 103 102 101 100 4 5 6 7 8 3 2 1 Time (min.)

  6. 107 106 105 • Decimal reduction time (DRT) -- Time for a _____ reduction in population size. Here DRT = ______ • If the goal is to reduce numbers to 102 then the size of the initial population will determine how long it will take, in this case, ____________ minutes. 104 103 102 101 100 4 5 6 7 8 3 2 1 Time (min.)

  7. Factors which determine the effectiveness of a control method (cont.) Spore formers vs. non-spore formers 107 106 # of viable cells __________________ 105 104 103 Vege-tative cells 102 101 100 4 5 6 7 8 3 2 1 Time (min.)

  8. Factors which determine effectiveness of a control agent (cont.) • Temperature and _______ of the environment • ___________________ of the agent • Mode of action of the agent • Microbistatic vs. microbicidal • Cellular target • Presence of ________________ compounds or inhibitors of the control agent

  9. Methods of Physical Control: Heat • _________ heat • Hot water, boiling water, steam • 60° - 135° C • Denatures proteins, nucleic acids • __________ heat • Ovens • 160° - >1000° C • Denatures, oxidizes At lower temperatures, moist heat is __________ effective than dry heat

  10. Moist heat methods • I. Boiling water -- ________ min. boiling kills all vegetative cells • II. Pasteurization -- Heating to temp. below boiling to kill specific pathogens and increase shelf-time • Batch method -- 63°-66° for 30 min. • ___________ method -- 71.6° for 15 sec. • Results in killing of most viruses and 97-99% reduction in veg. stages of bacteria and fungi • UHT (Ultra High Temp) -- 134° 1-2 ___________. • Milk can last up to 3 months unrefrigerated • Primary pathogen targets of pasteurization: ______________, Listeria, Mycobacterium, Campylobacter, Brucella

  11. Moist heat methods (cont.) • III. Steam under pressure • Highest temp. of moist heat at sea level -- _________° C • If ____________ increased, higher temps. can be reached • Autoclaving Commonly: _______° C at 15 PSI ________ min. at this temp. is very effective

  12. Effects on cellular proteins Text, Fig. 11.4

  13. Physical methods: radiation

  14. ____________ -- knocks electrons off atoms --> ions e.g. gamma rays, x-rays Damages DNA and proteins by breaking bonds -- Fig. 11.8 Exposure hazard to humans Penetrates ___________ and liquids Used in fruits & vegetables, now meats Non-ionizing -- excites atoms but doesn’t ionize e.g. ____________, sunlight Damages DNA by creating T-T dimers -- Fig. 11.8, 11.10 Relatively safe to use Doesn’t penetrate solids or liquids well ______________ sterilization, water treatment Physical methods: radiation

  15. Text, Fig. 11.8

  16. Text, Fig. 11.10

  17. Sonication -- Disruption using ___________ waves Filtration Text, Fig. 11.13 Other physical control methods

  18. Chemical control agents • I. Many kinds but most function by: • Disrupting __________________ • Altering ________________ and/or nucleic acid structure • II. Effectiveness is determined by: • Concentration • Contact time

  19. Major groups • ________________ • Phenol and its derivatives • Alcohols • Hydrogen peroxide • Detergents • Heavy ___________

  20. Halogens • Mainly _______________, also iodine and fluorine • Iodine “iodophors” most common iodine compound used in hospitals: Betadine, Povidone, etc. Less ____________ than free iodine due to slow release of free iodine. • 3 Chlorine forms: Cl2 (chlorine gas) OCl (hypochlorite -- common ‘bleach’) NH2Cl (chloramines) • In solution, these compounds combine with water to form hypochlorous acid (HOCl). This is the active form which destroys by ____________ • Effective against: bacteria, fungi, spores, viruses • Limitations: • ineffective at _____________ pH • ______________: light and O2 cause breakdown

  21. p-cresol (lysol) phenol OH OH CH3 Hexachlorophene (phisohex) OH OH Cl CH2 Cl Cl Cl Cl Cl Phenols • Phenolics affect protein function and/or disrupt membranes

  22. Alcohols • Ethanol -- 70% to 95% • Isopropanol -- more microbicidal but also more __________ • Destroy cell membranes, can coagulate proteins

  23. Hydrogen peroxide (H2O2) • Forms _______________ free radicals (e.g. superoxides, hydroxyl radicals: see last lecture) which are toxic to all cells • Also breaks down to H2O and O2, therefore is strongly effective against _____________.

  24. Detergents • All solubilize membranes and disrupt proteins Text, Fig. 11.3

  25. Detergents (cont.) • Two types: ___________ (charged) and non-ionic • Non-ionic and anionic detergents (like soaps) are not very microbicidal, although they may be very effective in sanitization. • _____________ detergents (like benzalkonium chloride) are the most effective ionic detergents.

  26. Heavy metals • Mainly only mercury and silver preparations are used now. • Merthiolate, mercurochrome, silver nitrate, etc. • Form ions which complex with cell components, stopping growth • Disadvantages: • _________________ • _________________ • Microbes can develop ___________________

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