Microbial Control Methods: Sterilization and Disinfection
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Questions and Answers

What is the primary material used in the construction of Seitz filters?

  • Glass particles
  • Ceramic
  • Diatomaceous earth
  • Asbestos (correct)
  • Which type of radiation has a high penetrative power and does not result in an appreciable increase in temperature?

  • Ionising radiation (correct)
  • UV radiation
  • Non-ionising radiation
  • Gamma radiation
  • What is the primary purpose of membrane filters in water purification?

  • To analyse water quality
  • To remove suspended particles
  • To remove bacteria and viruses (correct)
  • To remove heavy metals
  • What is the characteristic of sintered glass filters that makes them easy to clean?

    <p>Smooth surface</p> Signup and view all the answers

    What is the main limitation of using ultrasonic and sonic vibration for sterilisation?

    <p>Variable sensitivity of microorganisms</p> Signup and view all the answers

    What is the primary advantage of using candle filters for water purification?

    <p>Wide range of applications</p> Signup and view all the answers

    Which type of filter is commonly used for sterilisation and sterility testing?

    <p>Membrane filter</p> Signup and view all the answers

    What is the primary characteristic of non-ionising radiation?

    <p>Longer wavelength</p> Signup and view all the answers

    What is the main disadvantage of using asbestos filters?

    <p>Carcinogenic</p> Signup and view all the answers

    What is the primary application of ionising radiation in sterilisation?

    <p>Sterilisation of syringes and catheters</p> Signup and view all the answers

    Study Notes

    Methods of Sterilisation

    • Microbial control methods include physical agents, chemical agents, and mechanical removal methods.

    Physical Agents

    • Radiation: kills microorganisms by ionizing or non-ionizing radiation
      • Ionizing radiation: X-rays, gamma rays, and cosmic rays; high penetrative power; no appreciable increase in temperature; used for sterilizing plastics, syringes, catheters, grease fabrics, and metal foils
      • Non-ionizing radiation: electromagnetic rays with longer wavelength; absorbed as heat; used for rapid mass sterilization of prepacked syringes and catheters; e.g. UV rays
    • Heat: kills microorganisms by oxidation effects
      • Dry heat: uses oven; operated between 50°C to 250/300°C; holding period of 160°C for 1 hour is desirable; uses: sterilizing forceps, scissors, scalpels, swabs, and pharmaceutical products like liquid paraffin, dusting powder, fats, and grease
      • Flaming: inoculation loop or wire, the tip of forceps, and spatulas are held in a Bunsen flame till they are red hot
      • Incineration: destroys materials such as contaminated cloth, animal carcasses, and pathological materials
    • Moist heat: kills microorganisms by coagulating their proteins
      • Pasteurization: process of killing pathogens in milk; does not sterilize; milk is heated at 63°C for 30 minutes (Holder method) or at 72°C for 15-20 seconds (Flash process)
      • Boiling: kills vegetative forms of bacterial pathogens; hepatitis virus can survive up to 30 minutes of boiling; endospores can survive up to 20 hours or more of boiling
      • Steam at atmospheric pressure: uses steam sterilizer (Koch/Arnold steamer); consists of a tin cabinet with a conical lid; has a perforated tray above; for routine sterilization, exposure of 90 minutes is used; for media containing sugar and gelatin, exposure of 100°C for 20 minutes for 3 successive days is used; termed as Tyndallisation or Intermittent Sterilization
      • Steam under pressure: uses autoclave; works on the principle of steam under pressure; invented by Charles Chamberland in 1879; consists of a vertical or horizontal cylinder; has an opening for keeping materials to be sterilized; has a pressure gauge and safety valve; sterilization is carried out under pressure at 121°C for 15 minutes

    Chemical Agents

    • Act by protein coagulation, disruption of the cell membrane, removal of sulphydryl groups, and substrate competition
    • Alcohols: frequent use; no action on spores; concentration recommended 60-90% in water; uses: disinfection of clinical thermometer, disinfection of the skin – venipuncture
    • Aldehydes: frequent use; formaldehyde and glutaraldehyde; formaldehyde is bactericidal, sporicidal, and has a lethal effect on viruses; aqueous solutions are used in treatment of wounds
    • Gases: ethylene oxide is a colorless, highly penetrating gas with a sweet ethereal smell; effective against all types of microorganisms including viruses and spores; uses: sterilizing heart-lung machines, respirators, sutures, dental equipment, books, and clothing; also used to sterilize glass, metal, and paper surfaces, plastics, oil, some foods, and tobacco
    • Formaldehyde gas: widely employed for fumigation of operation theaters and other rooms
    • Beta propiolactone: used in fumigation; for sterilization, 0.2% BPL is used; has a rapid biocidal activity; very effective against viruses
    • Surface active agents and metallic salts: substances that reduce the surface tension; cations are widely used in the form of quaternary ammonium compounds; markedly bactericidal, active against Gram-positive organisms; no action on spores, tubercle bacilli, and viruses
    • Metallic salts: the salts of silver, copper, and mercury are used as disinfectants; act by coagulating proteins; marked bacteriostatic, weak bactericidal, and limited fungicidal activity

    Mechanical Removal Methods

    • Filtration: helps to remove bacteria from heat-labile liquids such as sera and solutions of sugar and antibiotics
    • Filters used: candle filters, asbestos filters, sintered glass filters, and membrane filters
    • Candle filters: widely used for purification of water; two types: unglazed ceramic filter (Chamberland filter) and diatomaceous earth filters (Berkefeld filter)
    • Asbestos filters: disposable single-use discs; high adsorbing tendency; carcinogenic; e.g. Seitz filter
    • Sintered glass filters: prepared by heat fusing powdered glass particles of graded size; cleaned easily; brittle; expensive
    • Membrane filters: made of cellulose esters or other polymers; uses: water purification and analysis, sterilization and sterility testing, and preparation of solutions for parenteral use

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    Description

    Test your knowledge on the various methods of microbial control, including physical and chemical agents, mechanical removal, and radiation. Learn about the different types of sterilization and disinfection methods, such as heat, radiation, and filtration. This quiz covers the principles and applications of microbial control in various fields.

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