Control of microbial growthtermsSome terms.Factors that influence effectivenessSlide 5Methods of ControlPhysical Controls:The autoclave: Moist heat and pressureSlide 9Slide 10Other controlsSlide 12Slide 13Slide 14Chemical Methods of ControlTestingDisk Diffusion MethodTypes of disinfectantsTypes of DisinfectantsSlide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Control of microbial growthSome terms to start with.terms•Biocide: kills biologicals•Germicide: Kills bacteria•Bacteriostasis: stops growth•Asepsis: absence of growthSome terms.•Sterilization: destruction of all life•Disinfecting: destruction of vegetative pathogens•Antisepsis: disinfection of living tissue•Sepsis: refers to microbial contamination.•Aseptic surgery techniques prevent microbial contamination of wounds.Factors that influence effectiveness•Number of microbes•Environmental influences•Time exposure•Microbial characteristics•Bacterial populations die at a constant logarithmic rate.Figure 7.1aMethods of Control•Physical•Chemical•Biological•Why is prevention best?Physical Controls:•Not for use on living organisms•Somehow, alter membrane permeability and / or structure of proteins and nucleic acidsThe autoclave: Moist heat and pressure•15psi, 121’c, 15 minutes•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 temperatureOther controls•Heat, dry heat takes longer•Low temperature•Desiccation•Osmotic Pressure•Radiation–Ionizing–No ionizing (UV)•Radiation damages DNA•Ionizing radiation (X rays, gamma rays, electron beams) •Nonionizing radiation (UV) •(Microwaves kill by heat; not especially antimicrobial)•Filtration Removes MicrobesChemical Methods of Control•May be used on living organisms•Factors that may effect disinfecting–Concentration of the disinfectant–What is to be disinfected•pH•Organic materials–Contact with microbe–timeTesting•Use dilution test–Three microbes are usedSalmonella choleraesuisStaphylococcus aureusPseudomonas aeruginosa–Metal carriers dipped and dried–Standard conditions 10 min at 20’CDisk Diffusion MethodTypes of disinfectants•Phenol and Phenolics•Halogens (iodine, chlorine) bind to aa of enzymes–Betadine iodophor (iodine bound to organic molecules)Types of DisinfectantsFigure 7.7•Phenol •Phenolics. Lysol•Bisphenols. Hexachlorophene, Triclosan–Disrupt plasma membranes•Alcohol’s usually by protein denaturizing•Heavy metals–Oligodynamic action–Denature proteins•Surface active Agents (detergents)Soap DegermingAcid-anionic detergents SanitizingQuarternary ammonium compoundsCationic detergents Bactericidal, Denature proteins, disrupt plasma membrane•Antibiotics–Worry about resistance–Not many used as preservative (Nisin, Natamycin)•Gaseous Chemostaerilizers–Ethylene oxide denatures proteins•Resistance to these methods depends on the microbe.•Peroxygens–Oxidizing agents–O3, H2O2, peracetic acidTypes of Disinfectants•Aldehydes–Inactivate proteins by cross-linking with functional groups (–NH2, –OH, –COOH, —SH)–Glutaraldehyde, formaldehydeTypes 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 cheeseTypes of DisinfectantsResistance to chemical