Lecture 7: Part 2: Infection Control

Part 2: Infection control Lecture 7 Memorize this table!!! Antiseptic, aseptic technique, bactericidal, bacteriostatic, disinfectant, fungicide, pasteurization, sanitization, sterilization, viricide Heating at 72C for 15 sec Ventilation Physical means of · isolation rooms with "air locks" 1. Heat 2. Filtration 3. Cold 4. High pressure 5. Desiccation (drying) 6. Osmotic pressure 7. Radiation · ultra-clean air (HEPA filters) ↳ positive pressure: air from the corridor cannot get into room -high to low pressure ↳ negative pressure: air from room cannot get into corridor -used as quarantine for infectious people Sterilization a. heat: hot air (160-180*C) for 1-2 hours ↳ autoclaving (moist heat): 121*C), 15 PSI, 15 min -will kill C. botulinum spores (industry std) -spore test for effectiveness b. irradiation c. filtration d. chemicals Controlling Microbial Growth: Most important consideration that determines the efficiency of sterilization is whether or not the object to be sterilized is free of organic matter (ie. blood, fecal material, tissue) ↳ the organic material may harden and scab, underneath the scab bacteria will survive Spore test (on autoclave) · uses Bacillus stearothermophilus spores · based on testing the ability of the autoclaving procedure to totally inactivate bacterial spores · ampule (test tubes) containing nutrient media and spores of a non-pathogenic bacteria are autoclaved WITH the object being steralized. The ampule is then incubated to test for growth · growth (lack of sterilization) is indicated by a change in the PH of the ampule growth media as a colour change as the spore has germinated and the growing or vegetative bacteria is using nutrients in the medium and producing acid or alkali compounds · negative test: purple (sterile) · positive test: yellow (not sterile) -PH of the medium changed because bacteria are still growing Chemical means of Controlling Growth: 1. hand soap: surface active agents 2. phenols: good disinfectants, remain active in presence of organic material 3. bisphenol: antiseptic 4. biguanides: antiseptic 5. quaternary ammonium compounds 6. alcohols: isopropyl/ethanol 7. heavy metals: silver, mercury 8. halogens: chlorine, iodine (can sterilize if used well) 9. aldehydes: sterilize (eg. glutaraldehyde) 10. ethylene oxide: gas that sterilizes 11. peroxygens: strong oxidizer, sterilizes Only some sterilize Halogens · Iodine ↳ available as tincture (solution in alcohol) or as an iodaphor (combination of iodine and organic molecules which release iodine slowly) · Chlorine ↳ strong oxidizing agent · Halogens can sterilize IF appropriate amount of active chemical is used and prolonged time of exposure Alcohols · kill bacteria and fung; but not endospores or non-enveloped viruses · mechanism is protein denaturation and disruption of lipid membranes · not good for treating wounds, as they cause a coagulation of proteins, creating an environment where bacteria can grow inside the scab · optimal concentration of ethanol is 70% (denaturation needs water to work) · isopropanol-rubbing alcohol is better than ethanol: does not evaporate as fast Relative Resistance of Microorganisms to Chemical Agents Least susceptible (hard to inactivate) Prions Endospores Mycobacteria Cysts of vegetative protozoa Vegetative protozoa Gram negative bacteria Fungi Naked viruses Most susceptible (easy to inactivate) Gram positive bacteria Enveloped viruses