MICRO-s10_Ch07 - 3/8/2010 Ch. 7 Objectives: Students should...

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Unformatted text preview: 3/8/2010 Ch. 7 Objectives: Students should be able to….. 1. Ch. 7: List 5 physical methods of controlling microbial List growth, and give an example of each. Why is moist heat growth and much more effective than dry air? much 2. Describe how to measure the effectiveness of a chemical Describe disinfectant. disinfectant 3. List 6 different types of chemical disinfectants and how List different and they damage microbial cells. Distinguish between biocidal biocidal and biostatic treatments. 4. W hat are the two most Resistant, and the two most What most and Sensitive microbial structures to antiseptic treatments? Sensitive microbial Why are these so? W hy Chapter 7 The Control of The Microbial Growth Microbial 1 3/8/2010 The Control of The Microbial Growth Microbial • Sepsis refers to microbial contamination. Sepsis refers • Asepsis is the absence of significant is contamination. contamination. – Aseptic surgery techniques prevent microbial Aseptic contamination of wounds. contamination Terminology 1. Sterilization: Removal of all microbial life. 2. Commercial Sterilization: Killing C. botulinum Killing botulinum endospores. 3. Disinfection: Removal of pathogens. 4. Antisepsis: Removal of pathogens from living Removal tissue. tissue. 5. Degerming: Removal of microbes from a limited Removal area. area. 6. Sanitization: Lower microbial counts on eating Lower utensils. utensils. 7. Biocide/Germicide: Kills microbes. 8. Bacteriostasis: Inhibiting, not killing, microbes. 2 3/8/2010 • Bacterial populations die at a constant, Bacterial constant logarithmic rate. logarithmic Figure 7.1a Effectiveness of antimicrobial Effectiveness treatment depends on: treatment 1. Number of microbes 2. Environment Environment • (organic matter, pH, (organic temperature, biofilms) biofilms 3. Time of exposure 4. Microbial Microbial characteristics characteristics Figure 7.1b 3 3/8/2010 Actions of Microbial Actions Control Agents Control 1. Alteration of Membrane permeability. a) Leakage b) Dissolution of PL bilayer Dissolution bilayer 2. Damage to Proteins. a) Destruction b) Denaturation 3. Damage to Nucleic Acids. a) Chemical alterations b) Destruction or mutations 7.1) Physical Methods 7.1) of Microbial Control of A. Heat – Thermal death point (TDP): Lowest Lowest temperature at which all cells in a culture are killed in 10 min. killed – Thermal death time (TDT): Time to kill all Time cells in a culture cells – Decimal reduction time (DRT): Minutes to kill Minutes 90% of a population at a given temperature 90% • Drop population by an order of magnitude!! 4 3/8/2010 A. Heat • Moist heat denatures denatures proteins proteins 1.Autoclave: Steam under Steam pressure pressure – Much higher Much temps reached at > 1 atm atm Figure 7.2 Moist Heat: (#2) • Pasteurization reduces spoilage organisms reduces and pathogens and • Equivalent treatments: – 63°C for 30 min. – High-temperature short-time: 72°C for 15 sec. time: 72 – Ultra-high-temperature: 140°C for <1 sec. temperature: 140 – Thermoduric organisms survive (& endospores). organisms endospores 5 3/8/2010 B. Dry Heat • Dry Heat Sterilization kills by oxidation Sterilization oxidation – Flaming – Incineration – Hot-air sterilization • Not as effective as Autoclave (moist heat, high press.) Hot-air Equivalent Equivalent treatments treatments 170˚C, 2 hr Autoclave 121˚C, 15 min Other Physical Methods Other of Microbial Control of C. Filtration removes microbes D. Low temperature inhibits microbial growth 1) Refrigeration 2) Deep freezing 3) Lyophilization E. High pressure denatures proteins F. Desiccation prevents metabolism G. Osmotic pressure causes plasmolysis causes plasmolysis 6 3/8/2010 Physical Methods of Microbial Physical Control Control H. Radiation damages DNA – Ionizing radiation (X rays, gamma rays, (X electron beams) •OH – Nonionizing radiation (UV) (UV) – (Microwaves kill by heat; not especially kill antimicrobial) antimicrobial) Figure 7.5 7.2) Chemical Methods 7.2) of Microbial Control of • Principles of effective disinfection – Principles Factors for consideration: 1. Concentration of disinfectant 2. Organic matter 3. pH 4. Time 7 3/8/2010 A. Chemical Methods of A. Microbial Control: Evaluation Evaluation • Evaluating a Disinfectant: 1. Use-dilution test: a) Metal rings dipped in test bacteria are dried. Metal rings b) Dried cultures placed in disinfectant for 10 min at 20°C. Dried disinfectant c) Rings transferred to culture media tto determine whether o Rings culture bacteria survived treatment. bacteria Evaluating a Disinfectant: 2. Disk-diffusion method: – Zone of Inhibition/ZOI = diameter of diameter clearing / sensitivity in mm. clearing Figure 7.6 8 3/8/2010 B. Types of Disinfectants 1. Phenol • • Denature proteins “chaotropic agents” Disrupt plasma Disrupt membranes membranes a) Phenolics: Lysol Lysol b) Bisphenols: Hexachlorophene, Triclosan Triclosan Figure 7.7 Types of Disinfectants 2. Biguanides: Chlorhexidine Chlorhexidine – Disrupt plasma membranes 3. Halogens: Iodine, Chlorine Chlorine – Oxidizing agents – Bleach iis hypochlorous s hypochlorous acid (HOCl) – Iodophores = betadine betadine (organic combo w/ I) 4. Alcohols: Ethanol, Isopropanol Isopropanol – Denature proteins, dissolve lipids 9 3/8/2010 Types of Disinfectants 5. Heavy Metals: Ag, Hg, Cu, Zn Ag, – Oligodynamic action • Very small amounts exert antimicrobial activity – Denature proteins • Highly cationic • Large, attractive surface Types of Disinfectants 6. Surface-Active Agents or “Surfactants” Active • Detergents Detergents • Emulsifiers COMPOUND Soap Acid-anionic detergents Quarternary ammonium ammonium compounds (“Quats”) -compounds Cationic detergents ACTIVITY Degerming Sanitizing Bactericidal, Denature proteins, Bactericidal, disrupt plasma membrane disrupt 10 3/8/2010 Types of Disinfectants 7. Chemical Food Preservatives a) Organic Acids Organic • Inhibit metabolism • Sorbic acid, benzoic acid, calcium propionate • Control molds and bacteria in foods and cosmetics b) Nitrite prevents endospore germination prevents endospore c) Antibiotics. Nisin and natamycin prevent spoilage of cheese Nisin and natamycin 8. Aldehydes – Inactivate proteins by cross-llinking with inking functional groups (–NH2, –OH, –COOH, —SH) OH, COOH, – Glutaraldehyde, formaldehyde 9. Gaseous Sterilants H C—CH Gaseous Sterilants 2 2 – Denature proteins – Ethylene oxide O 10. Peroxygens – Oxidizing agents – O3, H2O2, peracetic acid peracetic Microbial Characteristics Microbial and Microbial Control and 1. Prion 3D prot. strx 3D prot strx 2. Endospore resistance • & Protistan cysts Protistan 3. Gram– : LPS/OM porins porins 4. Unenveloped viruses • All have enhanced All relative resistance to chemical biocides to Figure 7.11 11 3/8/2010 Microbial Characteristics Microbial and Microbial Control and Chemical agent Phenolics Quats Chlorines Alcohols & Iodine Glutaraldehyde Effectiveness against Endospores Mycobacteria Poor Good None None Fair Fair Poor Good Fair Good ** Microbial control methods, especially biocides, are not ** equally effective against all microbes. ** equally 12 ...
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