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Chapter 7

Chapter 7. The Control of Microbial Growth. The Control of Microbial Growth. Sterilization: Removal of all microbial life Commercial Sterilization: Killing C. botulinum endospores Disinfection: Removal of pathogens Antisepsis: Removal of pathogens from living tissue

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Chapter 7

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  1. Chapter 7 The Control of Microbial Growth

  2. The Control of Microbial Growth • Sterilization: Removal of all microbial life • Commercial Sterilization: Killing C. botulinum endospores • Disinfection: Removal of pathogens • Antisepsis: Removal of pathogens from living tissue • Degerming: Removal of microbes from a limited area

  3. Terminology • Sanitization: Lower microbial counts on eating utensils • Biocide/Germicide: Kills microbes • Bacteriostasis: Inhibiting, not killing, microbes • Sepsis refers to microbial contamination. • Asepsis is the absence of significant contamination. • Aseptic surgery techniques prevent microbial contamination of wounds.

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

  5. Effectiveness of antimicrobial treatment depends on: • Number of microbes • Environment (organic matter, biofilms) • Time of exposure • Microbial characteristics • Temperture. • cioncentration Figure 7.1b

  6. Actions of Microbial Control Agents • Alternation of membrane permeability • Damage to proteins ( enzymes) • Damage to nucleic acids

  7. Physical Methods of Microbial Control • Heat • Thermal death point (TDP): Lowest temperature at which all cells in a liquid culture are killed in 10 min. • Thermal death time (TDT): the minimal length of Time to kill all cells in a liquid culture at a given temp. • Decimal reduction time (DRT): times in Minutes to kill 90% of a population at a given temperature

  8. Heat • Moist heat denatures proteins • Boiling • Autoclave: Steam under pressure Figure 7.2

  9. Physical Methods of Microbial Control • Pasteurization reduces spoilage organisms and pathogens • Equivalent treatments • 63°C for 30 min • High-temperature short-time (HTST) 72°C for 15 sec • Ultra-high-temperature (UTH): 140°C for <1 sec • Equivalent treatment. • Thermoduric organisms survive

  10. Physical Methods of Microbial Control • Dry Heat Sterilization kills by oxidation • Flaming • Incineration • Hot-air sterilization

  11. Physical Methods of Microbial Control • Filtration removes microbes • Heat sensitive material • High efficiency particulate air filters • Low temperature inhibits microbial growth • Refrigeration • Deep freezing • Lyophilization • High pressure denatures proteins • Desiccation prevents metabolism • Osmotic pressure causes plasmolysis

  12. Physical Methods of Microbial Control • Radiation damages DNA • Ionizing radiation (X rays, gamma rays, electron beams) • Wavelength less than 1 nm, Ionizing water • Short wave length, much more energy. • Nonionizing radiation (UV) (260nm) • (Microwaves kill by heat; not especially antimicrobial) • Microwaves

  13. Figure 7.5

  14. Chemical Methods of Microbial Control • Principles of effective disinfection • Concentration of disinfectant • Organic matter • pH • Time

  15. Chemical Methods of Microbial Control • Evaluating a disinfectant • Phenol coefficient test • Use-dilution test 1. Metal rings dipped in test bacteria are dried 2. Dried cultures placed in disinfectant for 10 min at 20°C 3. Rings transferred to culture media to determine whether bacteria survived treatment

  16. Chemical Methods of Microbial Control • Evaluating a disinfectant • Disk-diffusion method Figure 7.6

  17. Types of Disinfectants • Phenol • Lipid in Cell membrane • Phenolics. • Cresol ( Lysol) • Bisphenols. Hexachlorophene,lotion Triclosan in kitchenware Figure 7.7

  18. Types of Disinfectants • Biguanides. • Chlorhexidine • Disrupt plasma membranes • Mycobacterium relatively resist • Endospores and cyst not affected • Enveloped viruses and most vegetative cell affected

  19. Types of Disinfectants • Halogens. Iodine, Chlorine • Iodine combined with AA in enzymes and protein • Present as iodophore as povidone iodines or tincture • Chlorine Bleach is hypochlorous acid (HOCl) • Its strong oxidizing agent • Used in water disinfectant • Can present in many form as calcium hypochlorite, sodium hypochlorite, chloramines.

  20. Types of Disinfectants • Alcohols. Ethanol, isopropanol • Denature proteins, dissolve lipids • Not effect on spores or nonenveloped viruses Table 7.6

  21. Types of Disinfectants • Heavy Metals. Ag, Hg, Cu • Oligodynamic action • Denature proteins • Silver nitrate 1% used as antiseptic eye drops. • Cupper sulfate used to destroy green algae • Zinc chloride used as a mouth washing.

  22. Types of Disinfectants • Surface-Active Agents or Surfactants

  23. Types of Disinfectants • Chemical Food Preservatives • Organic Acids • Inhibit metabolism • Sorbic acid, benzoic acid, calcium propionate • Control molds and bacteria in foods and cosmetics • Potassium sorbate and sodium benzoate prevent spolige of acidic food. • Calcium propionate prevent growth of bacillus spores in bread. • Nitrite prevents endospore germination.

  24. Types of Disinfectants Antibiotics. • Nisin prevent endospore growth is an example of bacteriocin. • natamycin antifungal prevent spoilage of cheese Aldehydes • Inactivate proteins by cross-linking with functional groups (–NH2, –OH, –COOH, —SH) • Formaldehyde present in form of 37% aqueous solution • Glutaraldehyde, as 2% is bactericidal, tuberculocidal, virucidal in 10 min and sporocidal 3-10 hours.

  25. Types of Disinfectants • Gaseous Sterilants • Denature proteins • Ethylene oxide • Widely used in medical supplies. • Disadvantage they are suspected cacinogenes

  26. Types of Disinfectants • Peroxygens • Oxidizing agents • O3,used in stead of chlorine in water. • H2O2, • peracetic acid is sporocidal effect on endospore and viruses within 30 min and kill vegetative within 5 min.

  27. Microbial Characteristics and Microbial Control Figure 7.11

  28. Microbial Characteristics and Microbial Control

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