Chapter 9Controlling Microorganisms,Controlling Microbial Growth,AntimicrobialKills or prevent growth of microbesMicrobiocidalKills all microbesSterilantKills vegetative & endosporesMicrobiostaticOnly inhibits the growth of microbes,Sterilizationdestroy all microbial lifeDisinfectionreduces number of pathogenspose no danger of diseaseDecontaminationrenders contaminated surface safe to handleAntisepsiskills microorganisms on living tissue,Microbial Death Rate,Decimal reduction timeD-valuetime required to kill 90% of cellsHeat treatmentstemperaturetype of microorganismphysiological stateother substances,Decimal Reduction Time,Example: 1,000,000 (106)1 minute = 90% killed2 minutes = 100,000 (90%)3 minutes = 10,0004 minutes = 1,0005 minutes = 1006 minutes = 1 cell,Sterilization,Thermal death pointlowest temperaturekill all microorganisms in broth10 minutesThermal death timeminimal time kill all microorganisms (sterilize)liquid suspensionat given temperature,Conditions that Affect Antimicrobial Activity,Population densityLarger number the more timeConcentrationIncrease in concentration decreases in timeTime exposureIncrease exposure increases the number of killedTemperatureHigher Temp. greater number killedSubstrateAffect the efficiency of agentMicrobial characteristicsSusceptibility to different agents,Mechanisms of Microbial Agents,MODE OF ACTIONInterferes with cellular componentsCell membraneCell wallRibosomesGenetic material (DNA)EnzymesCytosol,Physical Controls,HeatMoistboilingkills most vegetative cells, not sterileautoclavesteam under pressure: 15 lbs./in2 at 121oC for 15 min.kills endosporesPasteurizationkills certain microorganismsBacteriaFungiSpores 5-10 min.5-10 min.5-10 min. 60-70oC50-60oC70-80oC,Pasteurization,Involves heating to temperatures below boiling for certain time periods (63-66oC for 30 minutes)Does not kill all microbes, but only those causing diseaseReduces the numbers of microbes that cause food spoilageNew method of Pasteurization Short term flash 71.6oC for15 seconds,Physical Controls,Drylong periods160oC for 2 hours171oC for 1 hour1. Causes oxidation of organic components of cell2. Used in sterilizing glassware and heat stable material i.e. pipettes,Physical controls,Colddoes not killmany die slowlyuseful in slowing growthRadiationUV lightsterilizes by damaging DNAIonizing: X-rays and gamma rayssterilizes by stripping electrons,Physical controls,Filtrationphysically removes microorganismsheat-sensitive liquidsmedia, vitamins, antibiotics, hormonesair filters (HEPA)Dryingnot sterilizationevaporationlyophilization,Osmotic strengthsalts and sugarsdamage cells by plasmolysispreserving foods,Specifications of an Ideal Chemical Agent,A. Broad spectrum of activity B. Soluble in water or alcohol C. Storage ability D. Nontoxic to humans or animals E. Active at normal temperatures F. Penetrating ability G. Safe for associated materials H. Odorless or pleasant smelling I. Inexpensive and readily available,Chemical controls,Antimicrobial agentschemotherapeutic agentsused to treat diseasegermicides and germistatsdisinfectants and antiseptics1200 germicidessold by 330 manufacturers in U.S.Selectiondamage the tissue or objectcontrol the target microorganism(s)purpose of treatment,Testing germicides,Paper disc methodgermicide placed on paper discdisc placed on agar seeded with microorganismafter incubation, observe zone of inhibition,Classes of germicides,Phenols and phenolicsdenature proteinsact on lipidsdisrupt cytoplasmic membraneExamples:ParacresolLysolHexachloropheneprescription use,Phenol: antiseptic,5% solution kills vegetative cellsLysol and hexachlorophene contain phenol-related compounds Less toxic and more effective as antimicrobial agentsLysol (Paracersol) disinfectantHexachlorophene antisepticChlorhexidine replaced hexachlorophene Kills by disrupt the cytoplasmic membrane Mode of action Disrupts cell membranes and their permeability Denature proteins Bactericidal or bacteriostatic, depending on concentration,Classes of germicides,Alcoholsdisrupt lipidsattack cytoplasmic membranedenature proteins50-70% solutions more effectiveincrease plasmolysis after membrane is damagedMode of actiona. Denature proteinsb. Dissolve lipids of cell membranes,Classes of germicides,Oxidizing agentsinactivate proteinsoxidizes functional groupsHalogensiodine: antisepticbetadine, tincture of iodinechlorine: disinfectantHydrogen peroxide (H2O2)3% solution-weak antisepticbroken down to water and oxygenbubbling when applied to skin,Halogens,Iodine Poor solubility in watera. Tincture of iodine alcoholic solution of iodine (antiseptic)b. Iodophor less irritating and non-staining (organic molecule with iodine)c. Antimicrobial against a broad spectrum of microbesd. Used to disinfect skin and water and sanitize food utensils; vapor can disinfect airMode of actiona. Acts as oxidizing agent capable of oxidizing metabolic compounds within cellb. Can bond with the amino acid tyrosine, thereby inactivating proteins,