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THE TERMINOLOGY OF MICROBIAL CONTROL • Sterilization-removing ALL microbial life; heat • Sterilant- a sterilizing agent • Commercial sterilization- killing C. botulinum endospores in food; used so food is not destroyed • Disinfection- removing pathogens not including endospore • Antisepsis- removing pathogens from living tissue • Degerming- mechanical removal of microbes from a limited area; using an alcohol swab • Sanitization- lowering microbial counts on eating utensils to a public health safety number THE TERMINOLOGY OF MICROBIAL CONTROL • Biocide/germicide- killing microbes • Fungicide- kills fungi • Virucide- inactivates viruses • Bacteriostasis- inhibiting, not killing, microbes • Sepsis- microbial contamination • Asepsis-the absence of significant microbial contamination • Aseptic surgery techniques prevent microbial contamination of wounds RATE OF MICROBIAL DEATH • Microbes die at a constant rate. • Each minute of treatment kills 90% of REMAINING microbes. EFFECTIVENESS OF TREATMENT • Depends on: • • • • Number of microbes Environment (organic matter, temperature, biofilms) Time of exposure Microbial characteristics ACTIONS OF MICROBIAL CONTROL AGENTS 1. Alteration of membrane permeability- damages lipids or proteins. 2. Damage to proteins- enzyme damage due denaturation 3. Damage to nucleic acids- cell can no longer replicate or carry on normal metabolic functions QUESTION: • Would a chemical microbial control agent that affects plasma membranes affect humans? 7-3 PHYSICAL METHODS OF MICROBIAL CONTROL HEAT • Thermal death point (TDP): lowest temperature at which all cells in a culture are killed in 10 min • Thermal death time (TDT): time during which ALL cells in a culture are killed • Decimal Reduction Time (DRT): Minutes to kill 90% of a population at a given temperature Figure 7.10 A comparison of the effectiveness of various antiseptics. MOIST HEAT STERILIZATION • Moist heat denatures proteins by breaking H bonds • Types: 1. Boiling- can kill most bacterial pathogens and viruses in 10 minutes; endospores up to 20 hours 2. Autoclave: steam under pressure; 15psi, 121C, 15 minutes; can kill endospores • Used for media, instruments, dressings, IV equipment, syringes, ets. • Time and temperature can change due to size • Steam must contact item’s surface Figure 7.2 An autoclave. Exhaust valve (removes steam after sterilization) Steam to chamber Safety valve Pressure gauge Operating valve (controls steam from jacket to chamber) Steam Door Steam chamber Air Perforated shelf Steam jacket To waste line Sediment screen Thermometer Automatic ejector valve Pressure regulator (thermostatically controlled; for steam supply closes on contact with pure steam when air is Steam supply exhausted) Figure 7.3 Examples of sterilization indicators. PASTEURIZATION • Reduces spoilage organisms and pathogens in some food and liquids without damaging taste of product • Equivalent treatments • • • • 63°C for 30 min High-temperature short-time: 72°C for 15 sec Ultra-high-temperature: 140°C for <1 sec Thermoduric(heat resistant) organisms survive DRY HEAT STERILIZATION • Kills by oxidation • • • • Dry heat Flaming Incineration Hot-air sterilization Equivalent Treatments Hot-Air Autoclave 170˚C, 2 hr 121˚C, 15 min FILTRATION • HEPA- removes microbes >0.3 µm • Membrane filtration- removes microbes >0.22 µm PHYSICAL METHODS OF MICROBIAL CONTROL • Low temperature inhibits microbial growth (bacteriostatic) • Refrigeration • Deep-freezing • Lyophilization • High pressure denatures proteins • Desiccation prevents metabolism • Osmotic pressure causes plasmolysis RADIATION • Ionizing radiation (X rays, gamma rays, electron beams) • • • • Damages DNA Can go through barriers Used by the food industry on meats, vegetables, and spices Also used on dental and medical supplies • Nonionizing radiation (UV) • Damages DNA • Has to be in direct contact • Microwaves kill by heat; not especially antimicrobial PRINCIPLES OF EFFECTIVE DISINFECTION • Concentration of disinfectant • Time • Substance the disinfectant is being used against: • Organic matter • pH EVALUATING A DISINFECTANT Use-Dilution Test Disk Diffusion Method • Metal rings dipped in test bacteria are dried • Dried cultures are placed in disinfectant for 10 min at 20°C • Rings are transferred to culture media to determine whether bacteria survived treatment • Filter paper is soaked with a chemical • Placed on an agar plate with an organism on it • Look for zones of inhibition Figure 7.6 Evaluation of disinfectants by the disk-diffusion method. Zone of inhibition Chlorine O-phenylphenol Hexachlorophene Quat Staphylococcus aureus (gram-positive) Chlorine O-phenylphenol Hexachlorophene Quat Escherichia coli (gram-negative) Chlorine O-phenylphenol Hexachlorophene Quat Pseudomonas aeruginosa (gram-negative) • If you wanted to disinfect a surface contaminated by vomit and a surface contaminated by a sneeze, why would your choice of disinfectant make a difference? 7-7 PHENOL AND PHENOLICS • Disrupt plasma membranes • Lysol • Bacteria BISPHENOLS • Hexachlorophene • Disrupt plasma membranes • Used in hospital soaps • Staphyloccocci and Streptococci • Triclosan • Disrupt plasma membranes • Found in soaps, toothpaste, cutting boards, plastic kitchenware • Bacteria and yeast BIGUANIDES • Chlorhexidine • Disrupts plasma membranes • Surgical hand scrubs and preoperative scrubs • Bacteria HALOGENS • Iodine • Alters protein synthesis and cell membranes • Bacteria, endospores, fungi, viruses • Chlorine • • • • Prevents enzyme system from functioning Bleach Disinfects drinking water, swimming pools, and sewage Bacteria and viruses ALCOHOLS • Ethanol, isopropanol • Denature proteins, dissolve lipids • Require water • Bacteria and fungi HEAVY METALS • Silver, Mercury, and Copper • Denatures proteins • Silver nitrate- may be used to prevent gonorrheal ophthalmia neonatorum • Silver sulfadiazine- used as a topical cream on burns • Copper sulfate- is an algicide SURFACE-ACTIVE AGENTS, OR SURFACTANTS Soap- mechanical removal of Degerming microbes Acid-anionic detergentsdairy utensils and equipment; bacteria Sanitizing Quaternary ammonium compounds (cationic detergents)fungicidal, amebicidal, virucidal Bactericidal, denature proteins, disrupt plasma membrane CHEMICAL FOOD PRESERVATIVES • Organic acids • Inhibit metabolism • Sorbic acid, benzoic acid, and calcium propionate • Control molds and bacteria in foods and cosmetics • Nitrite • Prevents endospore germination • Put in ham, bacon, hot dogs, sausage • Antibiotics • Nisin and natamycin prevent spoilage of cheese ALDEHYDES • Inactivate proteins by cross-linking • Bactericidal, tuberculocidal, virucidal, sporicidal • Used on hospital instruments, endoscopes, and respiratory therapy equipment • Glutaraldehyde, formaldehyde GASEOUS STERILANTS • Denature proteins • Sporicidal • Use: heat-sensitive material • Ethylene oxide PLASMA • Free radicals destroy microbes • Used for tubular instruments used for arthroscopic and laparoscopic surgeries SUPERCRITICAL FLUIDS • CO2 with gaseous and liquid properties • Use: medical implants(bones, tendons, ligaments) PEROXYGENS • Hydrogen Peroxide • Use: contaminated surfaces Figure 7.11 Decreasing order of resistance of microorganisms to chemical biocides. Table 7.7 The Effectiveness of Chemical Antimicrobials against Endospores and Mycobacteria