Microbiology - Chapter 8 Control of Microbes in the Environment
Microbiology - Chapter 8 Control of Microbes in the Environment BSC 302
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This 3 page Class Notes was uploaded by Sydney Coll on Friday October 14, 2016. The Class Notes belongs to BSC 302 at Marshall University taught by Dr. Mosher in Fall 2016. Since its upload, it has received 4 views. For similar materials see Microbiology in Biology at Marshall University.
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Date Created: 10/14/16
Chapter 8 – Control of Microbes in Environment Common Microbial Control Methods Disinfection: killing, inhibition, or removal of disease causing organisms o Usually used on inanimate objects Sterilization: destruction or removal of all viable organisms Antisepsis: prevention of infection of living tissue by microorganisms o Kill or inhibit growth of microorganisms when applied to tissue o Reduce number of pathogens on human skin o Sanitation: reduction of microbial population to levels deemed safe Chemotherapy: using chemicals to kill or inhibit growth of microorganisms within host cell o Agents that kill microorganisms or inhibit growth: Cidal agents kill Static agents inhibit growth Pattern of Microbial Death Microbes are not killed instantly Population death occurs exponentially Measure of agent’s killing efficiency o Decimal reduction time – time to kill 90% - z value o Once they recover, they may regain ability to reproduce and cause infection Filtration Reduces microbial population or sterilizes solutions of heat-sensitive materials by removing microorganisms Also used to reduce microbial populations in air Filtering liquids: o Membrane filters – porous membranes with defined pore sizes that remove microorganisms by physical screening Filtering air: o Cotton plugs on culture vessels o HEPA filters – used in laminar flow Physical Control Methods Heat Moist heat: o Destroys viruses, fungi, and bacteria o Boiling will not destroy spores and does not sterilize o Degraded nucleic acids, denatures proteins, and disrupts membranes Steam sterilization: o Above 100° C o Uses autoclave o Effective against all types of microbes Pasteurization: o Controlled heating at temperatures well below boiling o Process doesn’t sterilize but does kill pathogens and slows spoilage by reducing load of organisms present Dry heat sterilization: o Less effective than moist heat sterilization o Requires higher temperatures and longer exposure times Items subjected to 160-170° C for 2-3 hours o Oxidizes cell constituents and denatures proteins Dry heat incineration: o Used to sterilize inoculating loops Radiation o UV radiation: Wavelength 260 – most DNA absorbed Causes thymine dimers preventing replication and transcription UV limited to surface sterilization because it doesn’t penetrate glass, dirt films, water, and other substances o Ionizing radiation: Gamma radiation penetrates deep into objects Destroys endospores – doesn’t always work with viruses Used for sterilization, pasteurization of antibiotics, hormones, sutures, food Chemical Control Agents Disinfection – must be effective against wide variety of infectious, inanimate objects at low concentrations Antisepsis – overuse of antiseptics – antibiotic resistance Sterilization Whichever chemical is used, it must be effective in presence of organic matter’ Phenolics Denature proteins and disrupt cell membranes Lysol Active in presence of organic matter and remain active for long periods of time Alcohols Denature proteins and dissolve membrane lipids Ethanol and isopropanol Heavy Metals Effective but toxic Inactivate proteins and precipitate proteins Aldehydes Formaldehyde Highly reactive – combine with and inactivate nucleic acids and proteins Effectiveness of Agent Activity Population size – larger populations take longer to kill Population composition – microbes differ in sensitivity to antimicrobial agents Concentration or intensity of antimicrobial agents o Higher concentrations kill more rapidly Duration of exposure o Longer exposure = more organisms killed Temperature Local environment o pH, viscosity, etc. o organisms in biofilms are less susceptible to antimicrobial agents Efficiency Evaluations Dilution test: o Determine rate at which bacteria are destroyed by chemicals
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