Definitions. BIOL 3702: Chapter 8. Control of Microbes in the Environment. Mechanical Removal Methods. Pattern of Microbial Death

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1 Definitions Control of Microbes in the Environment u Sterilization - destruction or removal of all viable organisms from an object or environment (agent = sterilant) u Disinfection - killing, inhibition, or removal of pathogenic microorganisms (mainly pertains to inanimate objects) (agent = disinfectant) u Sanitization - reducing microbial populations to a safe level in accord with public health standards (agent = sanitizer) Slide No. 1 Slide No. 2 Definitions (cont.) Definitions (cont.) u Antisepsis - prevention of microbial infection on living tissue (agent = antiseptic) u Chemotherapy - prevention of microbial infection within living tissue Figure 8.2 u -cide - a suffix indicating that the agent will kill the kind of organism in question (e.g., viricide) u -static - a suffix indicating that the agent will prevent the growth of the type of organism in question (e.g., bacteriostatic) Slide No. 3 Slide No. 4 Pattern of Microbial Death u Microorganisms are not killed instantly when exposed to a lethal agent u Population death decreases by a constant fraction at constant intervals (exponential killing) u A microorganism is considered dead when it is unable to grow in conditions that would normally support its growth Slide No. 5 Mechanical Removal Methods u Filtration - sterilizes heat-sensitive liquids and gases by removing microorganisms rather than destroying them v Depth filters - thick fibrous or granular filters that remove microbes by physical screening, entrapment, or adsorption v Membrane filters - thin filters with defined pore sizes that remove microorganisms v High-efficiency particulate air (HEPA) filters - used in biological safety cabinets to sterilize air Slide No. 6 Dr. Cooper 1

2 AY Filter unit and filtration apparatus Figur e 8.4a Slide No. 7 Figur e 8.5 Slide No. 9 Slide No. 8 Figur e 8.6 Slide No. 10 Slide No. 12 Physical Methods o f Control u Heat v Moist heat Boiling water is effective against vegetative cells and eukaryotic spores, but not bacterial spores Autoclaving (steam under pressure) is effective against vegetative cells and most bacterial endospores Quality control - includes strips with Geobacillus stearothermophilus Dr. Cooper Slide No. 11 2

3 AY The Autoclave Figur e 8.7 Slide No. 13 v Pasteurization A process involving brief exposure to temperatures below the boiling point of water Reduces the total microbial population NOT STERILIZATION Often used for heat- sensitive materials v Tyndallization A process involving multiple brief exposures to temperatures below the boiling point of water Used for materials that cannot withstand the high temperatures of autoclaving Slide No. 14 v Dry heat c an be used t o s terilize moisture- sensitive materials s uch as powders, oils, and similar items Less efficient than moist heat Usually requires higher temperatures (160 to 170 C) and longer exposure times (2 to 3 hrs) v Incineration often used t o s terilize re- usable items, e.g., microbiological loops Figur e 8.8 Slide No. 15 Slide No. 16 u Radiation v Ultraviolet (UV) radiation is effective, but its use is limited t o s urface s terilization because UV radiation does not penetrate glass, dirt f ilms, water, and other s ubstances v Ionizing radiation (X rays, gamma rays, etc.) is effective and penetrates t he material Figur e 8.10 Dr. Cooper Slide No. 17 Slide No. 18 3

4 Chemical Agents in Control u Disinfectant must be effective against wide variety of infectious agents at low concentrations v Must be effective in the presence of organic matter;; should be stable in storage v Overuse of antiseptics such as triclosan has selected for triclosan resistant bacteria and possibly antibiotic resistant u Phenolics v Laboratory and hospital disinfectants v Act by denaturing proteins and cell membranes u Alcohol v Widely used disinfectants and antiseptics v Will not kill endospores v Act by denaturing proteins and possibly by dissolving membrane lipids Slide No. 19 Slide No. 20 u Halogens v Widely used antiseptics and disinfectant v Examples Ø Iodine: oxidizes cell constituents and iodinates cell proteins Ø Chlorine: oxidizes cell constituents u Heavy metals v Effective but usually toxic v Act by combining with proteins and inactivating them u Aldehydes v Reactive molecules that can be used as chemical sterilants, but may irritate the skin v Act by combining with proteins and inactivating them Figure 8.11 Slide No. 21 Slide No. 22 u Quaternary ammonium compounds v Cationic detergents of low toxicity v Uses: Ø Disinfectants for food utensils and small instruments Ø Skin antiseptic v Act by disrupting biological membranes and possibly by denaturing proteins u Sterilizing gases (e.g., ethylene oxide) v Used to sterilize heat-sensitive materials v Act by combining with proteins and inactivating them u Vapor-phase hydrogen peroxide has been used to decontaminate biological safety cabinets Slide No. 23 Slide No. 24 Dr. Cooper 4

5 Conditions Affecting Antimicrobial Activity u Population size - larger populations take longer to kill than smaller populations u Population composition - microorganisms differ markedly in their sensitivity to various agents u Concentration or intensity of the antimicrobial agent - higher concentrations or intensities are generally more efficient, but the relationship is not linear Conditions Affecting Antimicrobial Activity (cont.) u Duration of exposure - longer the exposure, the greater the number of organisms killed u Temperature - higher temperatures will often (but not always) increase the effectiveness of killing u Local environment - environmental factors, such as ph, viscosity, and concentration of organic matter, can profoundly influence the effectiveness of a antimicrobial agent Slide No. 25 Slide No. 26 Biological Control of Microbes u Emerging field showing great promise u Natural control mechanisms v Predation by Bdellovibrio v Viral-mediated lysis using pathogen specific bacteriophage lysins v Toxin-mediated killing using bacteriocins Annual Review of Microbiology 63: , 2009 Slide No. 27 Dr. Cooper 5