NORTH BIOL& 260 - Controlling Microbial Growth

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Controlling Microbial Growth What factors limit microbial growth In what situations are large microbial numbers undesirable Concept of Microbial Control Factors Which Affect Control Temp species type and status environment Physical Control Methods Heat Moist vs Dry Autoclaving pasteurization Filtration Cold Desiccation high osmotic pressure Radiation UV gamma rays Chemical Control Methods Factors which influence effectiveness Dilution time pH organic matter Types of Disinfectants Antiseptics Phenol and phenolics e g amphyl Halogens Chlorine iodine bromine Alcohols e g isopropyl alcohol Heavy metals Ag Hg Cu Zn Surface active agents soaps detergents Quaternary Ammonium Cmpds quats Aldehydes e g glutaraldehyde Microbial growth can be inhibited by temperature moisture control or by antimicrobial chemicals 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 concentration biofilms Time of exposure Microbial characteristics e g glycocalyx cell wall resistance Figure 7 1b Controlling Microbial Growth What factors limit microbial growth In what situations are large microbial numbers undesirable Concept of Microbial Control Factors Which Affect Control Temp species type and status environment Physical Control Methods Heat Moist vs Dry Autoclaving pasteurization Filtration Cold Desiccation high osmotic pressure Radiation UV gamma rays Chemical Control Methods Factors which influence effectiveness Dilution time pH organic matter Types of Disinfectants Antiseptics Phenol and phenolics e g amphyl Halogens Chlorine iodine bromine Alcohols e g isopropyl alcohol Heavy metals Ag Hg Cu Zn Surface active agents soaps detergents Quaternary Ammonium Cmpds quats Aldehydes e g glutaraldehyde Microbial growth can be inhibited by temperature moisture control or by antimicrobial chemicals 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 Autoclaving Moist heat denatures proteins Autoclave Steam under pressure 15 min at 121oC at 15 psi Figure 7 2 Pasteurization 63oC for 30 minutes 72oC for 15 seconds 140oC for 1 second Pasteurization reduces spoilage organisms and pathogens Physical Methods of Microbial Control Dry Heat Sterilization kills by oxidation Flaming Incineration Hot air sterilization Equivalent treatments Hot air Autoclave 170 C 2 hr 121 C 15 min Controlling Microbial Growth What factors limit microbial growth In what situations are large microbial numbers undesirable Concept of Microbial Control Factors Which Affect Control Temp species type and status environment Physical Control Methods Heat Moist vs Dry Autoclaving pasteurization Filtration Cold Desiccation high osmotic pressure Radiation UV gamma rays Chemical Control Methods Factors which influence effectiveness Dilution time pH organic matter Types of Disinfectants Antiseptics Phenol and phenolics e g amphyl Halogens Chlorine iodine bromine Alcohols e g isopropyl alcohol Heavy metals Ag Hg Cu Zn Surface active agents soaps detergents Quaternary Ammonium Cmpds quats Aldehydes e g glutaraldehyde Microbial growth can be inhibited by temperature moisture control or by antimicrobial chemicals Physical Methods of Microbial Control Filtration removes microbes by trapping them in filter Low temperature inhibits microbial growth Refrigeration Deep freezing 20oC or 80oC Lyophilization High pressure denatures proteins Desiccation prevents metabolism Osmotic pressure causes plasmolysis shrinkage of cytoplasm Physical Methods of Microbial Control Radiation damages DNA Ionizing radiation X rays gamma rays electron beams Nonionizing radiation UV surface sterilization only Microwaves kill by heat not especially antimicrobial Controlling Microbial Growth What factors limit microbial growth In what situations are large microbial numbers undesirable Concept of Microbial Control Factors Which Affect Control Temp species type and status environment Physical Control Methods Heat Moist vs Dry Autoclaving pasteurization Filtration Cold Desiccation high osmotic pressure Radiation UV gamma rays Chemical Control Methods Factors which influence effectiveness Dilution time pH organic matter Types of Disinfectants Antiseptics Phenol and phenolics e g amphyl Halogens Chlorine iodine bromine Alcohols e g isopropyl alcohol Heavy metals Ag Hg Cu Zn Surface active agents soaps detergents Quaternary Ammonium Cmpds quats Aldehydes e g glutaraldehyde Microbial growth can be inhibited by temperature moisture control or by antimicrobial chemicals Chemical Methods of Microbial Control Principles of effective disinfection Concentration of disinfectant Organic matter pH Time Chemical Methods of Microbial Control Evaluating a disinfectant Use dilution test 1 Metal rings dipped in test bacteria are dried 2 Dried cultures placed in diluted disinfectant according to manufacturer s instructions for min at 20 C 3 Rings transferred to culture media to determine whether bacteria survived treatment Chemical Methods of Microbial Control Evaluating a disinfectant Disk diffusion method Particular species are evaluated in each test Zone of inhibition must be at or beyond a certain diameter Figure 7 6 Controlling Microbial Growth What factors limit microbial growth In what situations are large microbial numbers undesirable Concept of Microbial Control Factors Which Affect Control Temp species type and status environment Physical Control Methods Heat Moist vs Dry Autoclaving pasteurization Filtration Cold Desiccation high osmotic pressure Radiation UV gamma rays Chemical Control Methods Factors which influence effectiveness Dilution time pH organic matter Types of Disinfectants Antiseptics Phenol and phenolics e g amphyl Halogens Chlorine iodine bromine Alcohols e g isopropyl alcohol Heavy metals Ag Hg Cu Zn Surface active agents soaps detergents Quaternary Ammonium


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