1MicrobiologyWith Diseases by TaxonomySecond EditionPowerPoint®Lecture SlidesCopyright © 2007 Pearson Education, Inc. publishing asBenjamin Cummings9Controlling Microbial Growth in the EnvironmentCopyright © 2007 Pearson Education, Inc. publishing as Benjamin CummingsTerminology of Microbial Control Sterilization Aseptic Disinfection/disinfectants Antisepsis/antiseptic DegermingCopyright © 2007 Pearson Education, Inc. publishing as Benjamin CummingsTerminology of Microbial Control Sanitization Pasteurization Suffix – stasis/-static Suffix – cide/-cidal2Copyright © 2007 Pearson Education, Inc. publishing as Benjamin CummingsMicrobial Death RatesFigure 9.1Copyright © 2007 Pearson Education, Inc. publishing as Benjamin CummingsAction of Antimicrobial Agents Many types of chemical and physical microbial controls Modes of action fall into two basic categories Alteration of cell walls or cytoplasmic membranes Interference with protein and nucleic acid structureCopyright © 2007 Pearson Education, Inc. publishing as Benjamin CummingsAlteration of Cell Walls and Membranes Cell wall maintains integrity of cell When disrupted, cannot prevent cell from bursting due to osmotic effects Cytoplasmic membrane contains cytoplasm and controls passage of chemicals into and out of cell When damaged, cellular contents leak out Viral envelope responsible for attachment of virus to target cell Damage to envelope interrupts viral replication Nonenveloped viruses have greater tolerance of harsh conditions3Copyright © 2007 Pearson Education, Inc. publishing as Benjamin CummingsDamage to Proteins and Nucleic Acids Protein function depends on 3-D shape Extreme heat or certain chemicals denature proteins Chemicals, radiation, and heat can alter or destroy nucleic acids Can produce fatal mutants Can halt protein synthesis through action on RNACopyright © 2007 Pearson Education, Inc. publishing as Benjamin CummingsSelection of Microbial Control Methods Ideally, agents should be: Inexpensive Fast-acting Stable during storage Control all microbial growth while being harmless to humans, animals, and objectsCopyright © 2007 Pearson Education, Inc. publishing as Benjamin CummingsFactors Affecting the Efficacy of Antimicrobial methods Nature of site to be treated Degree of susceptibility of microbes involved Environmental conditions that pertain4Copyright © 2007 Pearson Education, Inc. publishing as Benjamin CummingsSite to Be Treated Harsh chemicals and extreme heat cannot be used on humans, animals, and fragile objects Method and level of microbial control based on site of medical procedureCopyright © 2007 Pearson Education, Inc. publishing as Benjamin CummingsRelative Susceptibility of MicroorganismsFigure 9.2Copyright © 2007 Pearson Education, Inc. publishing as Benjamin CummingsRelative Susceptibility of Microorganisms 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 germicides kill vegetative bacteria, fungi, protozoa, and some viruses5Copyright © 2007 Pearson Education, Inc. publishing as Benjamin CummingsEnvironmental ConditionsFigure 9.3Copyright © 2007 Pearson Education, Inc. publishing as Benjamin CummingsMethods for Evaluating Disinfectants and Antiseptics Phenol coefficient Use-dilution test In-use testCopyright © 2007 Pearson Education, Inc. publishing as Benjamin CummingsPhenol Coefficient Evaluating the efficacy of disinfectants and antiseptics by determining the ratio of agent’s ability to control microbes to that of phenol Greater than 1.0 indicates that agent is more effective than phenol Has been replaced by newer methods6Copyright © 2007 Pearson Education, Inc. publishing as Benjamin CummingsUse-Dilution Test Metal cylinders dipped into broth cultures of bacteria and dried Contaminated cylinder immersed into dilution of disinfectant for 10 minutes Cylinders removed, washed, and placed into tube of medium for 48 h Most effective agent entirely prevents growth at highest dilution New standard procedure being developedCopyright © 2007 Pearson Education, Inc. publishing as Benjamin CummingsIn-Use Test Swabs taken from objects before and after application of disinfectant or antiseptic Swabs inoculated into growth medium and incubated Medium monitored for growth Accurate determination of proper strength and application procedure for each specific situationCopyright © 2007 Pearson Education, Inc. publishing as Benjamin CummingsPhysical Methods of Microbial Control Exposure to extremes of heat Exposure to extremes of cold Desiccation Filtration Osmotic pressure Radiation7Copyright © 2007 Pearson Education, Inc. publishing as Benjamin CummingsHeat-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 temperatureCopyright © 2007 Pearson Education, Inc. publishing as Benjamin CummingsMoist Heat Used to disinfect, sanitize, and sterilize 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 SterilizationCopyright © 2007 Pearson Education, Inc. publishing as Benjamin CummingsBoiling 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 boiling8Copyright © 2007 Pearson Education, Inc. publishing as Benjamin CummingsAutoclaving Pressure applied to boiling water prevents steam from escaping Boiling temperature increases as pressure increases Autoclave conditions – 121ºC, 15 psi, 15 minutesCopyright ©