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 woundsControl of Microorganisms: Physical & 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.pdfTerminologySterilization: removal/killing of ALL forms of microorganism from an objectDisinfection: reduction in the number of microorganisms with the goal of killing or inhibiting pathogensSanitation: 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, ex skin/oral cavityGeneral Resistance *Picture* Table 11.1Bacterial EndosporesFungal spores, protozoan cysts, some viruses and some bacterial vegetative cellsMost bacterial vegetative cells and fungi Most protozoaFactors Influencing Control• Population Type (composition) - What kind of microbe is present• Population Size- How many microbes present• Concentration/Intensity of Agent - 70% alcohols have the best killing effect• Duration of exposure - How long are you exposing to chemical agents• Temperature - environment• Local environmentpH, organic matter - bleach, hallogensControl Agents - NEED TO KNOW FOR EXAM• Physical Agents- Heat- Ionizing and non ionizing radiation• Mechanical Removal- Abrasion/Scrubbing- Filtration• Chemical Agents (many)- Quaternary Ammonium compounds- Ethylene oxide- Halogens- Phenolics- AlcoholsControl Agents *Picture* Figure 11.1Heat• The application of heat (high temperatures) is a very efficient way to kill most microbes - denatures protein, breakdowns membrane• 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 ° C) are generally required to efficiently destroy microorganismsMoist Heat *Picture*Autoclaving *Picture*- uses moist heat to get temps above 100º CPressurized steam• Needed for efficient killing of bacterial endosporesAutoclave Uses• Sterilizing:- Surgical/ medical instruments- Growth media & reagents- Biohazardous wastePasteurization (disinfection/sanitation)• Heat treatment of food products to reduce microbial levels• Problem: food quality altered by heat ex heating milk• Generally use 60-75º C for <30 minutes• Ultra Pasteurization: uses on food/other products, slightly higher temps and shorter timesMeasuring Effectiveness of Heat• Thermal Death Time (TDT)- Shortest time needed to kill ALL microorganisms at a specific temperature.Decimal Reduction Time (D Value) *Picture*- Time required to kill 90% of microorganisms at a specific temperature (a tenfold reduction or one log value)Mechanical ProcessesHand 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 (killing effect which continues to kill microbes after scrub)Chemical AgentsQuaternary Ammonium Compounds Quats• One of the most common disinfectants used• A cationic detergent• Uses- Food surfaces, hospital surfaces, general cleaning & disinfection, skin antisepsisQuaternary Ammonium Compounds• Advantages- Stable, low toxicity and irritation- Good action in presence of organics (breakup/damage material)- Good spectrum (how well these chemicals work)• Disadvantages- inactivated by hard water- Limited action on Mycobacterium and PseudomonasEvaluating 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 phenolEndGo to: Microbial
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