Slide 1Why is this important?Terminology of Microbial ControlMicrobial Death RatesAction of Antimicrobial AgentsAlteration of Cell Walls and MembranesDamage to Proteins and Nucleic AcidsThe Selection of Microbial Control MethodsFactors Affecting the Efficacy of Antimicrobial MethodsFactors Affecting the Efficacy of Antimicrobial MethodsFactors Affecting the Efficacy of Antimicrobial MethodsPhysical Methods of Microbial ControlHeat-Related MethodsMoist HeatMoist HeatMoist HeatMoist HeatMoist HeatDry HeatRefrigeration and FreezingDesiccation and LyophilizationFiltrationOsmotic PressureIonizing radiationNonionizing radiationChemical Methods of Microbial ControlPhenol and PhenolicsAlcoholsHalogensOxidizing AgentsSurfactantsHeavy MetalsAldehydesGaseous AgentsEnzymesAntimicrobialsDevelopment of Resistant MicrobesM I C R O B I O L O G YWITH DISEASES BY BODY SYSTEM SECOND EDITIONChapter 9Controlling Microbial Growth in the EnvironmentTHIRDWhy is this important?•Everyone should understand at least a little about how to control or eliminate microbial growth –Prevent contamination of food–Prevent human illness•Understand how and why different cleaners (bathroom and kitchen cleaners) work and how to make them work more effectivelyTerminology of Microbial ControlMicrobial Death Rates•Microbial death – the permanent loss of reproductive ability under ideal environmental conditions•Microbial death rate – usually found to be constant over time for any particular microbe under a particular set of conditionsAction of Antimicrobial Agents•Many types of chemical and physical microbial controls, but their modes of action (the way they work; how they affect microbial cells) fall into two basic categories–Those that disrupt the integrity of cells by adversely altering their cell walls or cytoplasmic membranes–Those that interrupt cellular metabolism and reproduction by interfering with the structures of proteins and nucleic acidsAlteration of Cell Walls and Membranes•Cell wall maintains cellular integrity by counteracting the effects of osmosis when the cell is in a hypotonic solution–If the wall is disrupted, it no longer prevents the cell from bursting as water moves into the cell by osmosis•Cytoplasmic membrane contains cytoplasm and controls passage of chemicals into and out of cell–When damaged, cellular contents leak out•Viral envelope is a membrane composed of proteins and phospholipids that is responsible for attachment of virus to target cell–Damage to envelope interrupts viral replication–Nonenveloped viruses have greater tolerance of harsh conditionsDamage to Proteins and Nucleic Acids•Proteins regulate cellular metabolism, function as enzymes in most metabolic reactions, and form structural components in membranes and cytoplasm•Protein function depends on 3-D shape that is maintained by hydrogen and disulfide bonds–When these bonds are broken by extreme heat or certain chemicals, the protein’s shape changes (denaturation)•Chemicals, radiation, and heat can alter or destroy nucleic acids–Can produce fatal mutations–Can halt protein synthesis through action on RNAThe Selection of Microbial Control Methods•Ideally, agents should be–Inexpensive–Fast-acting–Stable during storage–Capable of controlling growth and reproduction of every type of microbe while being harmless to humans, animals, and objectsFactors Affecting the Efficacy of Antimicrobial Methods•Site to Be Treated–Harsh chemicals and extreme heat cannot be used on humans, animals, and fragile objects–When performing medical procedures, the method and level of microbial control based on site of procedure because the site greatly affects the potential for subsequent infectionFactors Affecting the Efficacy of Antimicrobial Methods•Relative Susceptibility of Microorganisms–Death rates do vary among microorganisms and viruses–Effectiveness of germicides classified as high, intermediate, or low–High-level kill all pathogens, including endospores–Intermediate-level kill fungal spores, protozoan cysts, viruses, and pathogenic bacteria–Low-level kill vegetative bacteria, fungi, protozoa, and some virusesFactors Affecting the Efficacy of Antimicrobial Methods•Environmental Conditions–Temperature and pH affect death rates and the efficacy of antimicrobial methods–Warm disinfectants generally work better than cool ones–Acidic conditions enhance the antimicrobial effect of heat–Organic materials such as fat, feces, vomit, blood, and the intercellular secretions in biofilms interfere with penetration of heat, chemicals, and some forms of radiations, and in some cases these materials inactivate chemical disinfectantsPhysical Methods of Microbial Control•Heat-Related Methods–Moist Heat–Boiling–Autoclaving–Pasteurization–Ultrahigh-Temperature Sterilization–Dry Heat•Refrigeration and Freezing•Desiccation and Lyophilization•Filtration•Osmotic Pressure•Radiation–Ionizing Radiation–Nonionizing RadiationHeat-Related Methods•Effects of high temperatures–Denaturation of proteins–Interference with integrity of cytoplasmic membrane and cell walls–Disruption of structure and function of nucleic acids•Thermal death point – lowest temperature that kills all cells in broth in 10 minutes•Thermal death time – time to sterilize volume of liquid at set temperature•Decimal reduction time (D) – time required to destroy 90% of the microbes in a sampleMoist Heat•Used to disinfect, sanitize, sterilize, and pasteurize•Kills by denaturing proteins and destroying cytoplasmic membranes•More effective than dry heat; water better conductor of heat than air•Methods of microbial control using moist heat–Boiling–Autoclaving–Pasteurization–Ultrahigh-temperature sterilizationMoist Heat•Boiling–Kills vegetative cells of bacteria and fungi, protozoan trophozoites, and most viruses within 10 minutes at sea level–Temperature cannot exceed 100ºC at sea level; steam carries some heat away–Boiling time is critical–Water boils at lower temperatures at higher elevations; requires longer boiling time–Endospores, protozoan cysts, and some viruses can survive boiling–Effective for sanitizing restaurant tableware or disinfecting baby bottlesMoist Heat•Autoclaving–Pressure applied to boiling water prevents steam from escaping–Boiling temperature increases as pressure increases–Autoclave conditions – 121ºC, 15 psi, 15