BIOL 3702 Lecture OutlinePage 1 of 3Copyright © 2005 by Chester R. Cooper, Jr.Chapter 7 – Control of Microorganisms by Physical and Chemical AgentsDefinitions Sterilization - destruction or removal of all viable organisms from an object or environment Disinfection - killing, inhibition, or removal of pathogenic microorganisms (mainly pertains toinanimate objects) Antisepsis - prevention of microbial infection in living tissue Sanitization - reducing microbial populations to a safe level in accord with public healthstandards -cide - a suffix indicating that the agent will kill the kind of organism in question (e.g.,viricide) -static - a suffix indicating that the agent will prevent the growth of the type of organism inquestion (e.g., bacteriostatic)Pattern of Microbial Death Microorganisms are not killed instantly when exposed to a lethal agent Population death decreases by a constant fraction at constant intervals (exponential killing) A microorganism is considered dead when it is unable to grow in conditions that wouldnormally support its growthConditions Influencing Antimicrobial Activity Population size - larger populations take longer to kill than smaller populations Population composition - microorganisms differ markedly in their sensitivity to variousagents Concentration or intensity of the antimicrobial agent - higher concentrations or intensities aregenerally more efficient, but the relationship is not linear Duration of exposure - the longer the exposure, the greater the number of organisms killed Temperature - higher temperatures will often (but not always) increase the effectiveness ofkilling Local environment - environmental factors, such as pH, viscosity, and concentration oforganic matter, can profoundly influence the effectiveness of a particular antimicrobial agentPhysical Methods of Control Heat Moist heat Boiling water is effective against vegetative cells and eucaryotic spores Autoclaving (steam under pressure) is effective against vegetative cells and mostbacterial endosporesBIOL 3702 Lecture Outline Chapter 7Page 2 of 3Copyright © 2005 by Chester R. Cooper, Jr. Pasteurization A process involving brief exposure to temperatures below the boiling point of water Reduces the total microbial population Often used for heat-sensitive materials Dry heat can be used to sterilize moisture-sensitive materials such as powders, oils, andsimilar items Less efficient than moist heat Usually requires higher temperatures (160 to 170°C) and longer exposure times (2 to3 hrs) Low temperatures Freezing at -20°C doesn’t necessarily destroy microbes - inhibits growth by slowingmetabolism and removing available liquid water (actually can be used for long-termstorage of microbes) Refrigeration slows microbial growth by lowering rates of metabolism except for specialtypes of microbes (e.g., psycrophiles) Filtration - sterilizes heat-sensitive liquids and gases by removing microorganisms ratherthan destroying them Depth filters - thick fibrous or granular filters that remove microbes by physical screening,entrapment, or adsorption Membrane filters - thin filters with defined pore sizes that remove microorganisms,primarily by physical screening High-efficiency particulate air (HEPA) filters - used in laminar flow biological safetycabinets to sterilize air Radiation Ultraviolet (UV) radiation is effective, but its use is limited to surface sterilization becauseUV radiation does not penetrate glass, dirt films, water, and other substances Ionizing radiation (X rays, gamma rays, etc.) is effective and penetrates the materialChemical Agents in Control Phenolics Laboratory and hospital disinfectants Act by denaturing proteins Alcohol Widely used disinfectants and antiseptics Will not kill endospores Act by denaturing proteins and possibly by dissolving membrane lipidsBIOL 3702 Lecture Outline Chapter 7Page 3 of 3Copyright © 2005 by Chester R. Cooper, Jr. Halogens Widely used antiseptics and disinfectant Examples Iodine: oxidizes cell constituents and iodinates cell proteins Chlorine: oxidizes cell constituents Heavy metals Effective but usually toxic Act by combining with proteins and inactivating them Aldehydes Reactive molecules that can be used as chemical sterilants, but may irritate the skin Act by combining with proteins and inactivating them Quaternary ammonium compounds Cationic detergents of low toxicity Uses: Disinfectants for food utensils and small instruments Skin antiseptic Act by disrupting biological membranes and possibly by denaturing proteins Sterilizing gases (e.g., ethylene oxide) Used to sterilize heat-sensitive materials Act by combining with proteins and inactivating them Vapor-phase hydrogen peroxide has been used to decontaminate biological safety