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Ch. 7 - Microbiology

The Control of Microbial Growth

Norovirus. Most common cause of gastroenteritis. Most commonly spread fecal-oral route. No specific treatment. Lots of vomiting, diarrhea and stomach pain. Typically lasts 1-3 days, dehydration is a concern.
Sepsis. Refers to bacterial contamination.
Asepsis. Absence of significant contamination.
Aseptic surgery techniques. Prevent the microbial contamination of wounds.
Sterilization. Removing and destroying all microbial life.
Commercial sterilization. Killing C. botulinum endospores from canned goods.
Disinfection. Destroying harmful microorganisms.
Antisepsis. Destroying harmful microorganisms from living tissue.
Degerming. The mechanical removal of microbes from a limited area.
Sanitation. Lowering microbial counts on eating utensils to safe levels.
Biocide (germicide). Treatments that kill microbes.
Bacteriostasis. Inhibiting, not killing, microbes.
Rate of Microbial Death. Effectiveness of treatment depends on: Number of microbes. Environment (organic matter, temperature, biofilms). Time of exposure. Microbial characteristics.
Actions of Microbial Control Agents. Alteration of membrane permeability. Damage to proteins (enzymes). Damage to nucleic acids.
Heat. Denatures enzymes.
Thermal death point (TDP). Lowest temperature at which all cells in a liquid culture are killed in 10 min.
Thermal death time (TDT). Minimal time for all bacteria in a liquid culture to be killed at a particular temperature.
Decimal reduction time (DRT). Minutes to kill 90% of a population at a given temperature.
Moist heat. Denatures proteins.
Moist Heat Sterilization. Boiling. Free-flowing steam.
Autoclave. Steam under pressure. 121 C at 15 psi for 15 min. Kills all organisms and endospores. Steam must contact the item's surface. One of the BEST ways to sterilize equipment and kill microorganisms. Prions are resistant to normal autoclaving.
Moist Heat Sterilization. Large containers require longer sterilization times. Test strips are used to indicate sterility.
The Effect of Container Size on Autoclave Sterilization Times for Liquid Solutions*. *At higher altitudes, the atmospheric pressure is less. For example, to reach sterilizing temperatures (121°C) in Denver, Colorado, whose altitude is 5280 feet (1600 meters), the pressure shown on the autoclave gauge would need to be higher than 15 psi.
Pressure (psi in Excess of Atmospheric Pressure): 0,5,10,15,20,25,30. Temperature (°C): 100,110,116,121,126,135.
Pasteurization. Reduces spoilage organisms and pathogens.
Pasteurization (Heat). Equivalent treatments 63°C for 30 min. High-temperature short-time (HTST): 72°C for 15 sec. Ultra-high-temperature (UHT): 140°C for 4 sec.
Thermoduric. Organisms survive. May change properties of food. Raw Milk in CA, heated debates.
Dry Heat Sterilization. Kills by oxidation. Flaming Incineration-we perform this in our lab. Hot-air sterilization
Filtration. Passage of substance through a screen-like material. Used for heat-sensitive materials. High-efficiency particulate air (HEPA) filters remove microbes > 0.3 µm. Membrane filters remove microbes > 0.22 µm.
Physical Methods of Microbial Control. Low temperature has a bacteriostatic effect. Refrigeration. Deep-freezing. Lyophilization (freeze drying). High pressure denatures proteins.
Desiccation. Absence of water prevents metabolism.
Osmotic pressure. Uses salts and sugars to create hypertonic environment; causes plasmolysis. Curing of meat has been practiced since ancient times.
Ionizing radiation. (X rays, gamma rays, electron beams). Ionizes water to create reactive hydroxyl radicals. Damages DNA by causing lethal mutations.
Nonionizing radiation (UV, 260 nm). Damages DNA by creating thymine dimers.
Microwaves. Kill by heat; not especially antimicrobial.
Principles of Effective Disinfection. Concentration of disinfectant. Organic matter. pH. Time.
Use-Dilution Tests. Metal cylinders are dipped in test bacteria and dried. Cylinders are placed in disinfectant for 10 min at 20°C. Cylinders are transferred to culture media to determine whether the bacteria survived treatment.
Disk-Diffusion Method. Evaluates efficacy of chemical agents. Filter paper disks are soaked in a chemical and placed on a culture. Look for zone of inhibition around disks.
Phenol and Phenolics. Injure lipids of plasma membranes, causing leakage.
Bisphenols. Contain two phenol groups connected by a bridge. Hexachlorophene and triclosan. Disrupt plasma membranes.
Biguanides. Chlorhexidine. Used in surgical hand scrubs. Disrupt plasma membranes (Sponge and nail stick).
Halogens (Iodine). Tincture: solution in aqueous alcohol. Iodophor: combined with organic molecules. Impairs protein synthesis and alters membranes.
Halogens (Chlorine). Oxidizing agents; shut down cellular enzyme systems. Bleach: hypochlorous acid (HOCl). Chloramine: chlorine + ammonia.
Alcohols. Denature proteins and dissolves lipids. No effect on endospores and non-enveloped viruses. Ethanol and isopropanol. Require water. Why is this?
Heavy Metals and Their Compounds. Denature proteins. Ag (Silver nitrate). Hg (Mercuric chloride). Cu (Copper sulfate). Zn (Zinc chloride).
Oligodynamic action. Very small amounts exert antimicrobial activity.
Chemical Food Preservatives. Organic acids: Inhibit metabolism.
Antibiotics (Chemotherapy). Bacteriocins—proteins produced by one bacterium that inhibits another.
Silver nitrate. Used to prevent ophthalmia neonatorum, in prevention of transmission of gonorrhea.
Mercuric chloride. Prevents mildew in paint.
Copper sulfate. Is an algicide.
Zinc chloride. Found in mouthwash.
Nitrites and nitrates. Prevent endospore germination.
Sorbic acid, benzoic acid, and calcium propionate. Prevent molds in acidic foods.
Sulfur dioxide. Prevents wine spoilage, Sulfites (SO2).
Nisin and natamycin. Prevent spoilage of cheese.
Aldehydes. Inactivate proteins by cross-linking with functional groups.Used for preserving specimens and in medical equipment. Formaldehyde and ortho-phthalaldehyde. Glutaraldehyde is one of the few liquid chemical sterilizing agents.
Chemical Sterilization. Gaseous sterilants cause alkylation—replacing hydrogen atoms of a chemical group with a free radical. Cross-links nucleic acids and proteins. Used for heat-sensitive material. Ethylene oxide.
Plasma. Fourth state of matter, consisting of electrically excited gas. Free radicals destroy microbes. Used for tubular instruments.
Supercritical Fluids. CO2 with gaseous and liquid properties. Used for medical implants.
Peroxygens and Other Forms of Oxygen. Oxidizing agents. Used for contaminated surfaces and food packaging. O3, H2O2, and peracetic acid. Gerber baby water.
Created by: Jpereira72
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