Control of - Chapter 7 The Control of Microbial Growth The Control of Microbial Growth The Control of Microbial Growth Sepsis refers to microbial

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Unformatted text preview: Chapter 7 The Control of Microbial Growth The Control of Microbial Growth The Control of Microbial Growth Sepsis refers to microbial Sepsis contamination. contamination. Asepsis is the absence of significant Asepsis contamination. contamination. Aseptic surgery techniques prevent Aseptic microbial contamination of wounds. microbial Terminology 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 Sanitization: Lower microbial counts on eating utensils Biocide/Germicide: Kills microbes Bacteriostasis: Inhibiting, not killing, microbes Bacterial populations die at a constant logarithmic rate. Figure 7.1a Effectiveness of antimicrobial treatment depends on: Number of microbes Environment (organic matter, temperature, biofilms) Time of exposure Microbial characteristics Figure 7.1b Actions of Microbial Control Agents Alternation of membrane permeability Damage to proteins Damage to nucleic acids Physical Methods of Microbial Control Heat – 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 Heat Moist heat denatures proteins Autoclave: Steam under pressure Figure 7.2 Physical Methods of Microbial Control Pasteurization reduces spoilage organisms and pathogens Equivalent treatments – 63°C for 30 min – High­temperature short­time 72°C for 15 sec – Ultra­high­temperature: 140°C for <1 sec – Thermoduric organisms survive Physical Methods of Microbial Control Dry Heat Sterilization kills by oxidation – Flaming – Incineration – Hot­air sterilization Equivalent treatments Hot­air 170˚C, 2 hr Autoclave 121˚C, 15 min Physical Methods of Microbial Control Filtration removes microbes Low temperature inhibits microbial growth – Refrigeration – Deep freezing – Lyophilization High pressure denatures proteins Desiccation prevents metabolism Osmotic pressure causes plasmolysis Physical Methods of Microbial Control Radiation damages DNA – Ionizing radiation (X rays, gamma rays, electron beams) – Nonionizing radiation (UV) – (Microwaves kill by heat; not especially antimicrobial) Physical Methods of Microbial Control Figure 7.5 Chemical Methods of Microbial Control Principles of effective disinfection – Concentration of disinfectant – Organic matter – pH – Time Chemical Methods of Microbial Control Evaluating a disinfectant – Use­dilution test 1. 2. 3. Metal rings dipped in test bacteria are dried Dried cultures placed in disinfectant for 10 min at 20°C Rings transferred to culture media to determine whether bacteria survived treatment Chemical Methods of Chemical Methods of Microbial Control Evaluating a disinfectant – Disk­diffusion method Figure 7.6 Types of Disinfectants Types of Disinfectants Phenol Phenol Phenolics. Lysol Bisphenols. Bisphenols. Hexachlorophene, Triclosan Triclosan – Disrupt plasma Disrupt membranes membranes Figure 7.7 Types of Disinfectants Biguanides. Chlorhexidine – Disrupt plasma membranes Types of Disinfectants Halogens. Iodine, Chlorine – Oxidizing agents – Bleach is hypochlorous acid (HOCl) Types of Disinfectants Types of Disinfectants Alcohols. Ethanol, isopropanol – Denature proteins, dissolve lipids Table 7.6 Types of Disinfectants Heavy Metals. Ag, Hg, Cu – Oligodynamic action – Denature proteins Types of Disinfectants Surface­Active Agents or Surfactants Soap Degerming Acid­anionic detergents Quarternary ammonium compounds Cationic detergents Sanitizing Bactericidal, Denature proteins, disrupt plasma membrane 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 Types of Disinfectants Aldehydes – Inactivate proteins by cross­linking with functional groups (–NH2, –OH, –COOH, —SH) – Glutaraldehyde, formaldehyde Types of Disinfectants Gaseous Sterilants – Denature proteins – Ethylene oxide Types of Disinfectants Peroxygens – Oxidizing agents – O3, H2O2, peracetic acid Microbial Microbial Characteristics and Microbial Control Figure 7.11 Microbial Characteristics Microbial Characteristics and Microbial Control Chemical agent Phenolics Quats Chlorines Alcohols Glutaraldehyde Effectiveness against Endospores Mycobacteria Poor Good None None Fair Fair Poor Good Fair Good ...
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This note was uploaded on 01/16/2012 for the course BIOLOGY 251 taught by Professor Lancebowen during the Fall '10 term at Truckee Meadows Community College.

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