Controlling Microbial Growth in the Environment - PowerPoint Presentation

1. Controlling Microbial Growth in the Environment9

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3. Figure 9.1 A plot of microbial death rate.Constant percentageof the extant populationis killed each minute

4. Basic Principles of Microbial ControlAction of Antimicrobial AgentsAlteration of cell walls and membranesCell wall maintains integrity of cellWhen damaged, effects of osmosis cause cells to burst Cytoplasmic membrane contains cytoplasm and controls passage of chemicals into and out of cellWhen damaged, cellular contents leak outNonenveloped viruses can better tolerate harsh conditions

5. Basic Principles of Microbial ControlAction of Antimicrobial AgentsDamage to proteins and nucleic acidsProtein function depends on 3-D shapeExtreme heat or certain chemicals denature proteinsChemicals, radiation, and heat can alter or destroy nucleic acidsProduce fatal mutantsHalt protein synthesis through action on RNA

6. Basic Principles of Microbial ControlTell Me WhyWhy does milk eventually go "bad" despite being pasteurized?

7. The Selection of Microbial Control MethodsIdeally, agents should beInexpensiveFast-acting Stable during storageCapable of controlling microbial growth while being harmless to humans, animals, and objects

8. The Selection of Microbial Control MethodsFactors Affecting the Efficacy of Antimicrobial MethodsSite to be treatedHarsh chemicals and extreme heat cannot be used on humans, animals, and fragile objectsMethod of microbial control based on site of medical procedure

9. Figure 9.2 Relative susceptibilities of microbes to antimicrobial agents.

10. The Selection of Microbial Control MethodsFactors Affecting the Efficacy of Antimicrobial MethodsRelative susceptibility of microorganismsGermicide classificationHigh-level germicidesKill all pathogens, including endosporesIntermediate-level germicidesKill fungal spores, protozoan cysts, viruses, and pathogenic bacteriaLow-level germicidesKill vegetative bacteria, fungi, protozoa, and some viruses

11. Figure 9.3 Effect of temperature on the efficacy of an antimicrobial chemical.

12. The Selection of Microbial Control MethodsBiosafety LevelsFour levels of safety in labs dealing with pathogensBiosafety Level 1 (BSL-1)Handling microbes that do not cause disease in humansBiosafety Level 2 (BSL-2)Handling moderately hazardous agentsBiosafety Level 3 (BSL-3)All manipulations of microbes done in safety cabinetsBiosafety Level 4 (BSL-4)Handling microbes that cause severe or fatal diseaseLab space is isolated, and personnel wear protective suits

13. Figure 9.4 A BSL-4 worker carrying Ebola virus cultures.

14. The Selection of Microbial Control MethodsTell Me WhyWhy are BSL-4 suits pressurized? Why not just wear tough regular suits?

15. Physical Methods of Microbial ControlHeat-Related MethodsEffects of high temperaturesDenature proteinsInterfere with integrity of cytoplasmic membrane and cell wallDisrupt structure and function of nucleic acidsThermal death pointLowest temperature that kills all cells in broth in 10 minThermal death timeTime to sterilize volume of liquid at set temperature

16. Figure 9.5 Decimal reduction time (D) as a measure of microbial death rate.

17. Physical Methods of Microbial ControlHeat-Related MethodsMoist heat Used to disinfect, sanitize, sterilize, and pasteurizeDenatures proteins and destroys cytoplasmic membranesMore effective than dry heatMethods of microbial control using moist heatBoilingAutoclavingPasteurizationUltrahigh-temperature sterilization

18. Physical Methods of Microbial ControlHeat-Related MethodsMoist heat BoilingKills vegetative cells of bacteria and fungi, protozoan trophozoites, and most virusesBoiling time is criticalDifferent elevations require different boiling timesEndospores, protozoan cysts, and some viruses can survive boiling

19. Physical Methods of Microbial ControlHeat-Related MethodsMoist heat AutoclavingPressure applied to boiling water prevents steam from escapingBoiling temperature increases as pressure increasesAutoclave conditions: 121ºC, 15 psi, 15 minutes

20. Figure 9.6 The relationship between temperature and pressure.

21. Figure 9.7 An autoclave.PressuregaugeManualexhaust toatmosphereValve for steamto chamberExhaustvalveMaterial tobe sterilizedSteamjacketSteam supplyTrapThermometerDoorAirSafetyvalveSteam

22. Figure 9.8 Sterility indicators.Red mediummeans spores werekilled; autoclavedobjects aresterile.Yellow mediummeans spores areviable; autoclavedobjects are not sterile.After autoclaving, flexiblevial is squeezed to breakampule and releasemedium onto spore strip.Cap that allowssteam to penetrateFlexible plasticvialCrushable glassampuleNutrient mediumcontaining pHcolor indicatorEndospore stripIncubation

23. Physical Methods of Microbial ControlHeat-Related MethodsMoist heat PasteurizationUsed for milk, ice cream, yogurt, and fruit juicesNot sterilizationHeat-tolerant microbes survivePasteurization of milkBatch methodFlash pasteurizationUltrahigh-temperature pasteurization

24. Physical Methods of Microbial ControlHeat-Related MethodsMoist heat Ultrahigh-temperature sterilization140ºC for 1 to 3 seconds, then rapid coolingTreated liquids can be stored at room temperature

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26. Physical Methods of Microbial ControlHeat-Related MethodsDry heat Used for materials that cannot be sterilized with moist heatDenatures proteins and oxidizes metabolic and structural chemicalsRequires higher temperatures for longer time than moist heatIncineration is ultimate means of sterilization

27. Physical Methods of Microbial ControlRefrigeration and FreezingDecrease microbial metabolism, growth, and reproductionChemical reactions occur more slowly at low temperaturesLiquid water not availableRefrigeration halts growth of most pathogensSome microbes can multiply in refrigerated foodsSlow freezing is more effective than quick freezingOrganisms vary in susceptibility to freezing

28. Physical Methods of Microbial ControlDesiccation and LyophilizationDesiccation (drying) inhibits growth as a result of removal of waterLyophilization (freeze-drying) is used for long-term preservation of microbial culturesPrevents formation of damaging ice crystals

29. Figure 9.9 The use of desiccation as a means of preserving apricots in Pakistan.

30. Figure 9.10 Filtration equipment used for microbial control.Nonsterile mediumMembrane filterTo vacuum pumpSterile medium

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32. Figure 9.11 The roles of high-efficiency particulate air (HEPA) filters in biological safety cabinets.High-velocityair barrierLightSupply HEPAfilterBlowerExhaust HEPAfilterOutsideSafety glassviewscreen

33. Physical Methods of Microbial ControlOsmotic PressureHigh concentrations of salt or sugar in foods to inhibit growthCells in hypertonic solution of salt or sugar lose waterFungi have greater ability than bacteria to survive hypertonic environments

34. Physical Methods of Microbial ControlRadiationTwo types of radiationParticulate radiationHigh-speed subatomic particles freed from their atomsElectromagnetic radiationEnergy without mass traveling in waves at the speed of lightThe shorter the wavelength, the more energy the wave carriesAll types of radiation are described as either ionizing or nonionizingBased on the effects to chemicals within cells

35. Physical Methods of Microbial ControlRadiationIonizing radiationWavelengths shorter than 1 nmElectron beams, gamma ray, some X raysEjects electrons from atoms to create ionsIons disrupt hydrogen bonding, oxidize double covalent bonds, and create hydroxyl radicalsIons denature other molecules (DNA)Electron beams effective at killing microbes but do not penetrate wellGamma rays penetrate well but require hours to kill microbesX rays require long time to kill microbesNot practical for microbial control

36. Figure 9.12 A demonstration of the increased shelf life of food achieved by ionizing radiation.

37. Physical Methods of Microbial ControlRadiationNonionizing radiationWavelengths greater than 1 nmExcites electrons, causing them to make new covalent bondsAffects 3-D structure of proteins and nucleic acidsUV light causes pyrimidine dimers in DNAUV light does not penetrate wellSuitable for disinfecting air, transparent fluids, and surfaces of objects

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39. Physical Methods of Microbial ControlTell Me WhyWhy are Bacillus endospores used as sterility indicators (see Figure 9.8)?

40. Chemical Methods of Microbial ControlAffect microbes' cell walls, cytoplasmic membranes, proteins, or DNAEffect varies with differing environmental conditionsOften more effective against enveloped viruses and vegetative cells of bacteria, fungi, and protozoa

41. Chemical Methods of Microbial ControlPhenol and PhenolicsDenature proteins and disrupt cell membranesEffective in presence of organic matterRemain active for prolonged timeCommonly used in health care settings, labs, and homes Have disagreeable odor and possible side effects

42. Figure 9.13 Phenol and phenolics.

43. Chemical Methods of Microbial ControlAlcoholsIntermediate-level disinfectantsDenature proteins and disrupt cytoplasmic membranesMore effective than soap in removing bacteria from handsSwabbing skin with alcohol prior to injection removes most microbes

44. Chemical Methods of Microbial ControlHalogensInclude iodine, chlorine, bromine, and fluorineIntermediate-level antimicrobial chemicalsDamage proteins by denaturationWidely used in numerous applicationsIodine tablets, iodophores, chlorine treatment, bleach, chloramines, bromine disinfection, and the addition of fluoride to water and toothpastes

45. Figure 9.14 Degerming in preparation for surgery on a hand.

46. Chemical Methods of Microbial ControlOxidizing AgentsPeroxides, ozone, and peracetic acid Kill by oxidation of microbial enzymesHigh-level disinfectants and antisepticsHydrogen peroxide can disinfect and sterilize surfacesNot useful for treating open wounds because of catalase activityOzone treatment of drinking waterPeracetic acid is effective sporicide used to sterilize equipment

47. Chemical Methods of Microbial ControlSurfactants"Surface active" chemicalsReduce surface tension of solventsSoaps and detergentsSoaps have hydrophilic and hydrophobic ends Good degerming agents but not antimicrobialDetergents are positively charged organic surfactantsQuaternary ammonium compounds (quats) Low-level disinfectantsDisrupt cellular membranesIdeal for many medical and industrial applications

48. Figure 9.15 Quaternary ammonium compounds (quats).CetylpyridiniumBenzalkoniumHydrophobic tailQuaternary ammonium ions (quats)Ammonium ion

49. Chemical Methods of Microbial ControlHeavy MetalsHeavy-metal ions denature proteinsLow-level bacteriostatic and fungistatic agents1% silver nitrate once commonly used to prevent blindness caused by N. gonorrhoeaeThimerosal used to preserve vaccinesCopper controls algal growth

50. Figure 9.16 The effect of heavy-metal ions on bacterial growth.

51. Chemical Methods of Microbial ControlAldehydesCompounds containing terminal –CHO groupsCross-link functional groups to denature proteins and inactivate nucleic acidsGlutaraldehyde disinfects and sterilizesFormalin used in embalming and in disinfection of rooms and instruments

52. Chemical Methods of Microbial ControlGaseous AgentsMicrobicidal and sporicidal gases used in closed chambers to sterilize itemsDenature proteins and DNA by cross-linking functional groupsUsed in hospitals and dental officesDisadvantages Can be hazardous to people Often highly explosiveExtremely poisonousPotentially carcinogenic

53. Chemical Methods of Microbial ControlEnzymesAntimicrobial enzymes act against microorganismsHuman tears contain lysozymeDigests peptidoglycan cell wall of bacteriaUses of enzymes to control microbes in the environmentLysozyme is used to reduce the number of bacteria in cheesePrionzyme can remove prions on medical instruments

54. Chemical Methods of Microbial ControlAntimicrobialsAntibiotics and semisynthetic and synthetic chemicalsTypically are used to treat diseaseSome are used for antimicrobial control outside the body

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56. Chemical Methods of Microbial ControlMethods for Evaluating Disinfectants and AntisepticsPhenol coefficientEvaluates efficacy of disinfectants and antiseptics Compares to phenol an agent's ability to control microbesGreater than 1.0 indicates agent is more effective than phenolHas been replaced by newer methods

57. Chemical Methods of Microbial ControlMethods for Evaluating Disinfectants and AntisepticsUse-dilution testMetal cylinders dipped into broth cultures of bacteriaContaminated cylinder immersed into dilution of disinfectantCylinders removed, washed, and placed into tube of medium Most effective agents entirely prevent growth at highest dilutionCurrent standard test in the U.S.New standard procedure being developed

58. Chemical Methods of Microbial ControlMethods for Evaluating Disinfectants and AntisepticsKelsey-Sykes capacity testAlternative assessment approved by the European UnionBacterial suspensions added to the chemical being testedSamples removed at predetermined times and incubatedLack of bacterial reproduction reveals minimum time required for the disinfectant to be effective

59. Chemical Methods of Microbial ControlMethods for Evaluating Disinfectants and AntisepticsIn-use testSwabs taken from objects before and after application of disinfectant or antisepticSwabs inoculated into growth medium and incubatedMedium monitored for growthAccurate determination of proper strength and application procedure for each specific situation

60. Chemical Methods of Microbial ControlDevelopment of Resistant MicrobesLittle evidence that products containing antiseptic and disinfecting chemicals add to human or animal healthUse of such products promotes development of resistant microbes

61. Chemical Methods of Microbial ControlTell Me WhyMany chemical disinfectants and antiseptics act by denaturing proteins. Why does denaturation kill cells?