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Controlling Microbial Growth What factors limit microbial growth? In what situations are large microbial numbers undesi

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

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Controlling Microbial Growth What factors limit microbial growth? In what situations are large microbial numbers undesi

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  1. Controlling Microbial GrowthWhat 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

  2. 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

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

  4. 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

  5. Controlling Microbial GrowthWhat 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

  6. 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

  7. Autoclaving • Moist heat denatures proteins • Autoclave: Steam under pressure • 15 min at 121oC at 15 psi Figure 7.2

  8. Pasteurization 63oC for 30 minutes 72oC for 15 seconds 140oC for 1 second Pasteurization reduces spoilage organisms and pathogens

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

  10. Controlling Microbial GrowthWhat 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

  11. 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)

  12. 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)

  13. Controlling Microbial GrowthWhat 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

  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 • 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

  16. 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

  17. Controlling Microbial GrowthWhat 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

  18. Phenolics: Disruption of the plasma membrane O-phenylphenol (Lysol, Amphyl) Phenol Thymol Pine- Sol/pine oil (turpineol) Hexachlorophene

  19. Halogens Bromine and chlorine produces are strong oxidizers Iodine denatures proteins by breaking disulfide bonds Tincture of Iodine (I2 ); iodine denatures proteins by breaking disulfide bonds Povidone iodines (I linked to organic molecule) as in Betadine; denatures proteins by breaking disulfide bonds Bromine tablets (BCDMH -bromo-chloro-dimethyl-hydantoin)used in hot tubs, pools, kills by oxidation Sodium hypochlorite (NaOCl) in bleach is a strong oxidizing agent. Chlorine gas used in swim pools - oxidizing agent.

  20. Types of Disinfectants: Alcohols • Alcohols. Ethanol, isopropanol • Denatures proteins, dissolve lipids Table 7.6

  21. Controlling Microbial GrowthWhat 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) • Oxidizing Agents Microbial growth can be inhibited by temperature, moisture control or by antimicrobial chemicals

  22. Heavy metals Denature proteins by breaking disulfide bonds Mercurachrome antiseptic for wounds Copper sulfate (CuSO4) algicide Zinc chloride (ZnCl2) mouthwashes Silver nitrate (AgNO3) antiseptic for eyes, wounds

  23. Types of Disinfectants: Surface Active Agents • Surface-Active Agents or Surfactants (Soaps and Detergents)

  24. Quaternary Ammonium Compounds (Quats) Disruption of plasma membrane, denaturation of proteins Benzalkonium chloride (aka Zephiran) Roccal: lab disinfectant Cationic detergents Cetylpyridinium chloride (Cepacol)

  25. Types of Disinfectants:Aldehydes • Aldehydes • Inactivate proteins by cross-linking with functional groups (–NH2, –OH, –COOH, —SH) • Glutaraldehyde, formaldehyde Disinfection of hospital equipment, especially in respiratory therapy, for kidney dialysis machines, endoscopes glutaraldehyde

  26. Acids and Bases: Denaturation of Proteins, Dissolving Membranes NaOH (sodium hydroxide) in some floor cleaners NH4OH in ammonia, esp.good at breaking down lipids Benzoic acid in mouthwashes; benzoic acid, sorbic acid, citric acid, and ascorbic acid, in food products

  27. Gas Sterilants and Oxidizing Agents • Gaseous Sterilants • Denature proteins • Ethylene oxide to sterilize hospital equipment, disposable lab plasticware • Other oxidizing Agents • O3 (swim pools), H2O2(skin), Cl2 (swim pools), peracetic acid (dialysis equipment), bleach (sodium hypochlorite), bromine • Steals electrons from biomolecules, causing breakdown

  28. Microbial Characteristics and Microbial Control Figure 7.11

  29. Microbial Characteristics and Microbial Control

  30. Controlling Microbial GrowthWhat 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

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