Control of Microorganisms Physical & Chemical Agents Goal: removing pathogens from surfaces ••Surgical and other hospital equipment ••Laboratory equipment ••Food and food prep surfaces ••Any surface with known contamination by a pathogen ••Skin and skin wounds Control of MicroorganismsPhysical & Chemical Agents ••Caveat ––Getting rid of microbes just to be “more clean” or to have a perfectly disinfected environment is detrimental. It can lead to: ••A build-up of resistance by the microbe to the agent being used. ••limiting your immune system from building an immunity to specific microbes. ••Obsessive cleaning behavior! ••http://www.tufts.edu/med/apua/Pubs/Articles/EID6_01.pdf Terminology ••Sterilization: removal/killing of all forms of microorganism from an object ••Disinfection: reduction in the number of microorganisms with the goal of killing or inhibiting pathogens Terminology ••Sanitation: reduction in microbial numbers considered safe by public health agencies. Usually applied to the food industry. ••Antisepsis: the killing or inhibiting of microorganisms on living tissue General Resistance !¬Bacterial Endospores ¬Fungal spores, protozoan cysts, some viruses and some bacterial vegetative cells ¬Most bacterial vegetative cells and fungi ¬Most protozoa Factors Influencing Control ••Population Type (composition) ––What kind of microbe is present ••Population Size ––How many microbes present ••Concentration/Intensity of Agent ••Duration of exposure ••Temperature ••Local environment ––pH, organic matter Control Agents ••Physical Agents ––Heat ––Ionizing and non ionizing radiation ••Mechanical Removal ––Abrasion/Scrubbing ––Filtration ••Chemical Agents (many) ––Quaternary Ammonium compounds ––Ethylene oxide ––Halogens ––Phenolics ––Alcohols Control AgentsHeat ••The application of heat (high temperatures) is a very efficient way to kill most microbes. ••What temperature do you need? ––Most microbes survive at temperatures below 40° C (104 ° F) ––Temperatures of 40-60° C inhibit the growth of many microbes and may even destroy some types. →®Temperatures >60° C (140 ° F) are generally required to efficiently destroy microorganisms Moist Heat Autoclaving ••Moist heat above 100º C ••Pressurized steam ••Needed for efficient killing of bacterial endospores Autoclave Uses ••Sterilizing: ––Surgical/ medical instruments ––Growth media & reagents ––Biohazardous waste Pasteurization ••Heat treatment of food products to reduce microbial levels ••Problem: food quality altered by heat ••Generally use 60-75º C for <30 minutes Measuring Effectiveness of Heat ••Thermal Death Time (TDT) ––Shortest time needed to kill all microorganisms at a specific temperature. Mechanical Processes Hand Washing ••Pathogens – not as tightly attached as “normal” commensal bacteria. ••Mechanical removal ––Water and scrubbing only – Yes it does remove microbes ! ––Water and soap – better ––Water and antibacterial soaps/products – probably same as water and soap – although may have some residual effect (keeps microbes off hands after scrub) Chemical Agents Quaternary Ammonium Compounds ••One of the most common disinfectants used ••A cationic detergent ••Uses ––Food surfaces, hospital surfaces, general cleaning & disinfection, skin antisepsis Quaternary Ammonium Compounds ••Advantages ––Stable, low toxicity and irritation ––Good action in presence of organics ––Good spectrum ••Disadvantages ––inactivated by hard water ––Limited action on Mycobacterium and Pseudomonas Evaluating Effectiveness ••Phenol Coefficient ––Compares activity of phenol to other agents ––Coefficient ••< 1.0 not as effective as phenol ••=1.0 same ••>1.0 better than phenolEnd ••Go to: Microbial
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