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Control of microbial growth

Control of microbial growth. Some terms to start with. terms. Biocide : kills biologicals Germicide : Kills bacteria Bacteriostasis : stops growth A sepsis : absence of growth. Some terms. Sterilization : destruction of all life Disinfecting : destruction of vegetative pathogens

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Control of microbial growth

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  1. Control of microbial growth Some terms to start with.

  2. terms • Biocide: kills biologicals • Germicide: Kills bacteria • Bacteriostasis: stops growth • Asepsis: absence of growth

  3. Some terms. • Sterilization: destruction of all life • Disinfecting: destruction of vegetative pathogens • Antisepsis: disinfection of living tissue • Sepsis: refers to microbial contamination. • Aseptic surgery techniques prevent microbial contamination of wounds.

  4. Factors that influence effectiveness • Number of microbes • Environmental influences • Time exposure • Microbial characteristics

  5. Bacterial populations die at a constant logarithmic rate. Figure 7.1a

  6. Methods of Control • Physical • Chemical • Biological • Why is prevention best?

  7. Physical Controls: • Not for use on living organisms • Somehow, alter membrane permeability and / or structure of proteins and nucleic acids

  8. The autoclave: Moist heat and pressure • 15psi, 121’c, 15 minutes • Thermal death point (TDP): Lowest temperature at which all cells in a culture are killed in 10 min. • Thermal death time (TDT): Time to kill all cells in a culture • Decimal reduction time (DRT): Minutes to kill 90% of a population at a given temperature

  9. Other controls • Heat, dry heat takes longer • Low temperature • Desiccation • Osmotic Pressure • Radiation • Ionizing • No ionizing (UV)

  10. Radiation damages DNA • Ionizing radiation (X rays, gamma rays, electron beams) • Nonionizing radiation (UV) • (Microwaves kill by heat; not especially antimicrobial)

  11. Filtration Removes Microbes

  12. Chemical Methods of Control • May be used on living organisms • Factors that may effect disinfecting • Concentration of the disinfectant • What is to be disinfected • pH • Organic materials • Contact with microbe • time

  13. Testing • Use dilution test • Three microbes are used Salmonella choleraesuis Staphylococcus aureus Pseudomonas aeruginosa • Metal carriers dipped and dried • Standard conditions 10 min at 20’C

  14. Disk Diffusion Method

  15. Types of disinfectants • Phenol and Phenolics • Halogens (iodine, chlorine) bind to aa of enzymes • Betadine iodophor (iodine bound to organic molecules)

  16. Types of Disinfectants • Phenol • Phenolics. Lysol • Bisphenols. Hexachlorophene, Triclosan • Disrupt plasma membranes Figure 7.7

  17. Alcohol’s usually by protein denaturizing • Heavy metals • Oligodynamic action • Denature proteins

  18. Surface active Agents (detergents) Soap Degerming Acid-anionic detergents Sanitizing Quarternary ammonium compoundsCationic detergents Bactericidal, Denature proteins, disrupt plasma membrane • Antibiotics • Worry about resistance • Not many used as preservative (Nisin, Natamycin)

  19. Gaseous Chemostaerilizers • Ethylene oxide denatures proteins • Resistance to these methods depends on the microbe.

  20. Types of Disinfectants • Peroxygens • Oxidizing agents • O3, H2O2, peracetic acid

  21. Types of Disinfectants • Aldehydes • Inactivate proteins by cross-linking with functional groups (–NH2, –OH, –COOH, —SH) • Glutaraldehyde, formaldehyde

  22. Types of Disinfectants • Chemical Food Preservatives • Organic Acids • Inhibit metabolism • Sorbic acid, benzoic acid, calcium propionate • Control molds and bacteria in foods and cosmetics • Nitrite prevents endospore germination • Antibiotics. Nisin and natamycin prevent spoilage of cheese

  23. Resistance to chemical Biocides

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