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Physical and Chemical Control of Microbes

Physical and Chemical Control of Microbes. Relative resistance of microbes. Highest resistance Bacterial endospores prions Moderate resistance Mycobacterium tuberculosis Protozoan cysts Non-enveloped viruses Least resistance most vegetative cells Fungal spores enveloped viruses

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Physical and Chemical Control of Microbes

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  1. Physical and Chemical Control of Microbes

  2. Relative resistance of microbes • Highest resistance • Bacterial endospores • prions • Moderate resistance • Mycobacterium tuberculosis • Protozoan cysts • Non-enveloped viruses • Least resistance • most vegetative cells • Fungal spores • enveloped viruses • Protozoan trophozoites

  3. Terms • Sterilization– A process that destroys all microbes, including endospores. • Disinfection– A process to destroy most microbes, not endospores. • Antisepsis – Disinfectants applied directly to exposed body surfaces • -cide: the agent will kill the organism • (e.g.,bacteriocide, viricide, fungicide). • - static: the agent will inhibit the growth of the organism • (e.g., bacteriostatic, fungistatic).

  4. Factors that influence action of antimicrobial agents: • Number of microbes • Nature of microbes in the population • Concentration or dosage of agent • Mode of action of the agent

  5. Methods of Control • Chemical • Halogens • Alcohols • Aldehydes • Ethylene Oxide • Physical • Heat • Radiation • Filtration

  6. 1.Heat • denaturation of proteins • Moist Hat • Dry heat

  7. Moist heat • Autoclave 15 psi / 121oC /15-20min • sterilization • Protein coagulation = 15 psi http://www.frankshospitalworkshop.com/equipment/autoclaves_equipment.html

  8. Intermittent sterilization • Tyndallization , by john tyndal • unpressurized steam at 100oC 15-20 min for 3 days • a process that kills spore-forming microorganisms, involves exposing the material to elevated temperatures (killing the vegetative cells) • then incubation at 37C (to allow spores to germinate to form new vegetative cells) • and then exposure to elevated temperatures again (to kill the newly germinated vegetative cells) • used to sterilize heat-sensitive materials or to kill particularly resistant endospores.

  9. Pasteurization • Invented by Louis Pasture 72°C for 15 seconds 135°C for 2-3 s 63°C for 30 minutes

  10. Dry heat Dry heatusing higher temperatures than moist heat. • bacteria incinerator – ~800 oC combusts & dehydrates cells • dry ovens – 160 °C for 2 hours - coagulate proteins

  11. Methods of Control • Chemical • Halogens • Alcohols • Aldehydes • Ethylene Oxide • Physical • Heat • Radiation • Filtration

  12. 2.Radiation • Ionizing radiation – deep penetrating power, breaks DNA, • gamma rays, X-rays • used to sterilize medical supplies & food products • Nonionizing radiation – little penetrating power to sterilize air, water & solid surfaces • UV light creates thymine dimer, which interfere with replication

  13. Gamma rays X rays UV light

  14. 3.Filtration • physical removal of microbes by passing a gas or liquid through filter • used to sterilize heat sensitive liquids & air in hospital isolation units & industrial clean rooms

  15. Chemical control • Halogens • Alcohols • Aldehydes • Ethylene Oxide (Gas)

  16. 1. Halogens • Chlorine – Cl2, hypochlorites (chlorine bleach), • Disinfectant water supply • Iodine - I2, iodophors (betadine) • Iodopovidone (Povidone-iodine)is an antiseptic used for skin disinfection before and after surgery. • Denature proteins

  17. 2.Alcohols • Ethyl, isopropyl in solutions of 70% • Act as surfactants dissolving membrane lipids and coagulating proteins of vegetative bacterial cells and fungi • Not sporicidal

  18. 3. Aldehydes • Glutaraldehyde & formaldehyde ( formalin) kill by alkylating protein , DNA and RNA. • glutaraldehyde in 2% solution (Cidex) used as sterilant for heat sensitive instruments • formaldehyde - disinfectant, preservative , toxicity limits use

  19. 4.Ethylene Oxide • colorless gas that is flammable and explosive. • sporicidal • The main disadvantages associated with ETO are the lengthy cycle time (~14h) , the cost, and its potential hazards to patients and staff but it can sterilize heat- or moisture-sensitive medical equipment . (CDC)

  20. Others • Hydrogen Peroxide (H2O2) 3% • Phenolics : Phenol , Lysol , tricolsan • Chlorhexidine

  21. Cold temperatures • slows the growth of microbes • refrigeration 0-15oC & freezing <0oC • used to preserve food, media and cultures

  22. Desiccation or drying • gradual removal of water from cells, leads to metabolic inhibition • Lyophilization “freeze-drying” a process in which water is removed from a product after it is frozen

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