Physical and Chemical Control of Microorganisms

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 ___________________