Chapter 5 of Microbiology
Chapter 5 of Microbiology 2300
Popular in Microbiology 2300
Popular in Microbiology
This 8 page Class Notes was uploaded by Lauren Dennis on Thursday September 22, 2016. The Class Notes belongs to 2300 at Georgia State University taught by Dr. Fuhua Lu in Fall 2016. Since its upload, it has received 13 views. For similar materials see Microbiology 2300 in Microbiology at Georgia State University.
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Date Created: 09/22/16
Chapter 5: Control of Microbial Growth Sterilization: removal of all organism o Filtration, heat chemicals, and irradiation Disinfection: eliminates most pathogrns o Disinfects: inanimate objects and surfaces o Antiseptics: used on living tissues Pasteurization: brief heat treatment to reduce organisms that cause food spoilage o Louis Pastuer o Wine, Beer, and Milk Decontamination: treatment to reduce pathogens to safe levels Sanitization: substantially reduces microbial population to meet health standards Preservation: process used to delay spoilage of perishable items o Approaches: Daily: Washing or scrubbing with soap o Soap: agent that aids removal Hospitals: Prevent nosocomial infections o Most common o Easily preventative o Sterilize instruments Laboratories: Aseptic technique and sterile media for growth Contaminated materials: disposal bins Food production: Heat, gamma-radiation approved to treat foods Chemicals prevent spoilage o Toxicity is a disadvantage Water Treatment: Chlorine to disinfect water o Can react with naturally occurring DBP o Some are resistant o Selection: Types: Resistant: endospores, protozoan cycts and ocyts, mycobacterium, Pseudomonas species, and naked viruses Extent of contamination: Commercial effectiveness is determined by decimal radiation time o [D] value o time to kill 90% of bacterium Environment Risk: Critical item:s contact with skin o Needles and scapels Semi critical: instruments contact with mucous membrane but no prentration o Endodpores Non-critical: unbroken skin only o Little risk of transmission o Stethoscope o Heat: Physical Method of Treatment Boiling (100C) Destroys most microorganisms and viruses Does not destroy endospores Pasteurization Not sterilization but reduces Increase shelf life of food HTST Method o Heat: 72C and held for 15 seconds UHT o Heat for 140C; held for several seconds; and then cooled Pressurized steam o Autoclave used to sterilize with steam Heat water; steam; increase pressure o Achieves sterilization at 121C/ 15psi/ for 15 minutes Fights against endospores Flash autoclave: 135C in 3 minutes Prions: 132C for 1 to 4.5 hours Commercial canning process o Destroys Clostridium botulinum endospores Dry heat: o Not as effective Longer times and higher temperatures 200C for 1.4 hours vs. 121C for 15 minutes Incineration method Oxidizes cells to ashes Destroys medical waste and animal carcasses Flaming laboratory inoculation loop incinerates bacteria o Sterile loop Heat sensitive materials require other methods: Filtration Irradiation High-pressure o Other Methods Filtration: Membrane: removes microbes from fluids in air Liquid o Heat sensitive fluids o Membrane filters allow liquids to flow o Depth filters trap microbes: electron charge Radiation: Shorter wavelengths and higher frequency = more energy Ionizing radiation o Gamma radiation and X-rays and Electron accelerators Cause damages to DNA and potentially altering the plasma membrane o Used to sterilize medical equipment and surgical supplies and medications UV Radiation: Non-ionizing radiation o Damages DNA and thyme dimers Breakdown/alter the DNA o Destroys microbes in air, surfaces o Limitations: Poor penetration power Thin films of coverings o Chemicals: Formulations generally contain more than one antimicrobial agent FDA- antiseptics EDA – disinfectants Germicidal agents grouped with potentially Sterliants: destroys all High-level disinfectants: destroy viruses and vegative cells o Not endospores Intermediate disinfectants: vegative cells, fungi, most viruses o Not endospores Low-Level disinfectants: fungi, vegative bacteria, enveloped bacteria o Not mycobacterial, naked viruses, or endospores o Selection of appropriate material Toxicity: benefits against risk of use Activity in the presence of organic material Germicides inactive in presence of organic material Compatibility with material being treated Liquids do not mix with electrical equipment Residue: Toxic and corrosive Cost and availability Storage and stability Concentrated stock relieves issues Environmental risk Germicidal agent harmful to environment? o Chemicals as Controls: Phenolics, a.k.a carbolic acid One of the earliest disinfectants Active ingredient in Lysol Destroy plasma membrane, denature proteins Kills most vegetative cells Can kill mycobacterium at high concentrations Not reliable on all groups of viruses Triclosan and hexachlorophene used in soaps and lotions Quaternary ammonium compounds, a.k.a Quats Cationic detergents, nontoxic o Used to disinfect food preparation surfaces Reduces surface tension o Aids in removal of dirt and organic matter o Facilitates mechanical removal of organisms Positive charge attracts Quats to negative charge of cell surface o Reacts with membrane o Not effective on endospores, mycobacteria and naked viruses Alcohols Solutions of 60% - 80% isopropyl or ethyl alcohol kill vegetative bacteria and fungi, not effective against endospores and some naked viruses Coagulation of proteins and essential enzymes, damage to lipid membranes Commonly used as antiseptic and disinfectant Limitations o Evaporates quickly, limiting contact time o May damage material such as rubber and some plastics Aldehydes Destroy organisms by inactivating proteins and DNA 2% glutaraldehyde solution most widely used liquid sterilant o Orthophthalaldehyde studied as alternative Formalin is solution made from formaldehyde o Kills bacteria and inactivate viruses o Also used for specimen preservation Biguanides Most effective member of group is chlorhexidine o Extensively used in antiseptics o Relative low toxicity o Destroys wide range of organisms Ethylene oxide Useful gaseous sterilant o Destroys microbes including endospores and viruses Reacts with proteins Useful in sterilizing heat or moisture sensitive items Limitations o Mutagenic and potentially carcinogeni o Peroxygens: Include hydrogen peroxide and peracetic acid Powerful oxidizing agents, readily biodegradable Less toxic than ethylene oxide and glutaraldehyde Hydrogen peroxide o More effective on inanimate object o Useful as disinfectant Leaves no residue, doesn’t damage most materials o Hot solutions used in food industry o Vapor-phase can be used as sterilant Peracetic acid o More potent then hydrogen peroxide o Effective on organic material Can be used on wide range of material o Chemicals as Controls: Metal compounds Compounds combine with enzymes and proteins High concentrations of many metals toxic to human tissue o Silver still used as disinfectant Creams containing silver sulfadiazine used to prevent secondary infections Also available on bandages for wound care Ozone O 3 Unstable form of oxygen Powerful oxidizing agent Used as alternative to chlorine o As disinfectant for drinking and waste water o Halogens: Common disinfectants Oxidizing proteins and other cell components Chlorine Destroys all types of organisms and viruses Used as disinfectant o Caustic to skin and mucous membranes Chlorine dioxide replacing chlorine in many applications Iodine Kills vegetative cells o Not reliable with endospores skin antiseptic: skin damage, staining, and allergies can be a problem Tincture of iodine: iodine in ethanol Iodophore: iodine complexed with organic carrier Wescodyne and Beadyne o Chemical Perservatives: Numerous chemicals are used as preservatives Formaldehyde, Quats, and phenols Weak organic acids often used as food preservatives Alter cell membrane function; o Interfere with energy transformation Benzoic, ascorbic and propionic acids o Used in bread, cheese and juice Nitrates and nitrites used in processed meats Inhibits germination of endospores and growth of vegetative cells Have been shown to be potent carcinogen o Physical Perservatives: Low temperature storage Low temperatures slow down or stop enzymatic reactions of mesophiles and thermophiles o Some psychrotrophies still able to grow Freezing as means of food preservation o Kills up to 50% of microbes Reducing water availability Decreasing water availability accomplished by salting or drying food o Addition of salt increases environmental solutes Causes cellular plasmolysis o Numerous bacteria can continue to grow in high salt environments Staphylococcus aureus can survive in high salt concentrations o Lyophilization (freeze drying) Widely used to preserve foods like coffee, milk and meats
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