Microbial Control and Sterilization Techniques
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Questions and Answers

What is the primary action of ethylene oxide (ETO) on microbial cells?

  • Alkylating protein functional groups (correct)
  • Altering carbohydrate structures
  • Inhibiting cell wall synthesis
  • Dissolving cell membranes

    • Which method is used to prevent the explosive tendency of ethylene oxide gas?

  • Cooling to low temperatures
  • Mixing with inert gases like CO2 (correct)
  • Using metal containers
  • Diluting with water

    • For which of the following items is ethylene oxide NOT typically used for sterilization?

  • Petri dishes
  • Plastic syringes
  • Heart-lung machines
  • Glass surgical instruments (correct)

    • What quantity of KMnO4 is recommended for generating formaldehyde gas in a 1000 cubic feet volume room?

    <p>150 gm</p> Signup and view all the answers

    What type of precautions are standard in infection control protocols?

    <p>Universal precautions applicable to all patients</p> Signup and view all the answers

    What is the primary action of UV radiation in sterilization?

    <p>Denaturation of bacterial proteins</p> Signup and view all the answers

    Which chemical method is recognized for its lower toxicity compared to formaldehyde?

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

    What type of radiation is employed for the sterilization of disposable items such as syringes and swabs?

    <p>Gamma radiation</p> Signup and view all the answers

    What is the main bactericidal action of phenols during sterilization?

    <p>Cell membrane damage</p> Signup and view all the answers

    What is a key limitation of using alcohols as skin antiseptics?

    <p>Ineffective against bacterial spores</p> Signup and view all the answers

    Which disinfectant is commonly used in the form of iodophores for preoperative skin degerming?

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

    Which of the following is NOT a characteristic of hypochlorites as disinfectants?

    <p>Completely safe for all materials</p> Signup and view all the answers

    In cold sterilization, which type of radiation method is primarily utilized?

    <p>Ionizing radiation</p> Signup and view all the answers

    Which of the following statements about chlorine as a disinfectant is false?

    <p>Has significant virucidal action</p> Signup and view all the answers

    What is the primary use for formaldehyde gas in sterilization procedures?

    <p>Fumigation of heat-sensitive equipment</p> Signup and view all the answers

    What is the primary advantage of using saturated steam over dry heat for sterilization?

    <p>Saturated steam has a better penetrative power than dry heat.</p> Signup and view all the answers

    At what pressure and temperature does an autoclave typically operate to ensure effective sterilization?

    <p>1210C at 15 psi</p> Signup and view all the answers

    Which type of filtration is specifically designed to sterilize heat-labile materials?

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

    Which type of filter is manufactured in various grades of porosity for purification purposes?

    <p>Earthenware filters</p> Signup and view all the answers

    What pore sizes are the most commonly used for membrane filters in various applications?

    <p>0.22 µm and 0.45 µm</p> Signup and view all the answers

    What is the function of HEPA filters in microbiology laboratories?

    <p>They remove particles 0.3 µm or larger from the air.</p> Signup and view all the answers

    What material is commonly used in the construction of membrane filters?

    <p>Polymeric materials</p> Signup and view all the answers

    Which type of filter is utilized by pressing the piston of a syringe to force fluid through?

    <p>Syringe filters</p> Signup and view all the answers

    What is the primary purpose of using filtration for sterilization?

    <p>To sterilize solutions that could be damaged by heat</p> Signup and view all the answers

    Which of the following is true about the principle of autoclaving?

    <p>Increased pressure raises the temperature at which water boils.</p> Signup and view all the answers

    What is sterilization primarily intended to achieve?

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

    What distinguishes disinfection from sterilization?

    <p>Disinfection reduces the number of harmful organisms.</p> Signup and view all the answers

    Which method uses a high temperature below boiling point for microbial control?

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

    What is the primary action of moist heat sterilization?

    <p>Coagulation and denaturation of proteins</p> Signup and view all the answers

    How long should materials be held in a hot air oven at 160°C for effective sterilization?

    <p>2 hours</p> Signup and view all the answers

    What is the correct temperature and duration for the holder method of pasteurization?

    <p>63°C for 30 minutes</p> Signup and view all the answers

    Which of the following is NOT a physical method of microbial control?

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

    What is the process known as Tyndallization?

    <p>Exposure to steam at 100°C over three days</p> Signup and view all the answers

    Which method is primarily used for sterilizing materials that can withstand high temperatures but are affected by steam?

    <p>Hot air oven sterilization</p> Signup and view all the answers

    What type of heat sterilization kills organisms through protein denaturation and oxidative damage?

    <p>Dry heat</p> Signup and view all the answers

    Which of the following is a characteristic of disinfectants?

    <p>They are used to inhibit microbial growth on inanimate surfaces.</p> Signup and view all the answers

    What is the purpose of sanitization in microbial control?

    <p>Mechanical removal of microbes</p> Signup and view all the answers

    In the flash method of pasteurization, what is the heating temperature and duration?

    <p>72°C for 15-20 seconds</p> Signup and view all the answers

    What is the main limitation of drying as a method of microbial control?

    <p>Its effectiveness varies significantly.</p> Signup and view all the answers

    Study Notes

    Microbial Control

    • Microbial control aims to stop reproduction or kill bacteria.
    • Sterilization eliminates all microorganisms, including spores, from an object or surface.
    • Disinfection destroys pathogens but not necessarily spores, reducing microorganisms to a non-harmful level.
    • Antiseptics are chemical disinfectants safe for living tissues, preventing infection by inhibiting microbial growth.
    • Sanitization is a cleaning technique that physically removes microbes.

    Physical Methods

    • Sunlight has bactericidal effects due to UV and heat rays. Natural sterilization of water in tanks, rivers, and lakes occurs due to sunlight.
    • Drying inhibits bacterial growth as moisture is essential for their survival. However, this method is unreliable and primarily of theoretical importance.
    • Heat is the most reliable sterilization method.
      • Dry heat kills organisms through protein denaturation, oxidative damage, and toxic effects of elevated electrolytes.
      • Moist heat kills microorganisms by coagulating and denaturing their enzymes and structural proteins.

    Dry Heat Methods

    • Red heat involves heating materials in a Bunsen burner flame until they become red hot. Used for inoculating wires, forceps tips, spatula surfaces, and needles.
    • Flaming involves passing materials through a Bunsen burner flame without letting them become red hot. Used for glass slides, scalpels, and culture tube/bottle mouths.
    • Incineration burns materials to ashes using an incinerator. Used for soiled dressings, animal carcasses, bedding, and pathological material.
    • Hot air oven is the most widely used dry heat sterilization method, used for heat-resistant materials like glassware, forceps, scissors, and scalpels, as well as oils, jellies, and powders.
      • Holding temperatures and times:
        • 160°C for 2 hours
        • 170°C for 1 hour
        • 180°C for 30 minutes
        • Oils, glycerol, and dusting powder should be sterilized at 150°C for 1 hour.

    Moist Heat Methods

    • Moist heat is divided into three forms:
      • Temperature below 100°C: Pasteurization and water bath
      • Temperature of 100°C: Boiling, steam, and Tyndallisation
      • Temperature above 100°C: Autoclave
    • Pasteurization involves heating a fluid below boiling point to kill pathogenic vegetative microorganisms.
      • Holder method: 63°C for 30 minutes, rapid cooling to 13°C or lower.
      • Flash method: 72°C for 15-20 seconds, rapid cooling to 13°C or lower.
      • Ultra High Temperature (UHT): 140-150°C for 1-3 seconds followed by rapid cooling to 13°C or lower.
    • Boiling at 100°C for 10-30 minutes kills vegetative cells. Spores require prolonged boiling times.
      • Used for disinfecting medical and surgical equipment in emergencies or field conditions when sterility is not essential.
    • Tyndallisation (intermittent sterilization) involves exposing materials to steam at 100°C for 20 minutes on three consecutive days.
      • Kills vegetative forms, allowing spores to germinate between heatings. Subsequent heatings kill the newly formed vegetative forms.
      • Used for sterilizing egg, serum, or sugar-containing media.
    • Autoclave uses steam under pressure to sterilize materials at a temperature above 100°C.
      • Holding period/working temperature: 121°C for 15 minutes (15 psi pressure).
      • Autoclave used for sterilizing culture media, rubber material, gowns, dressings, gloves, instruments, water-containing materials, permeable materials, wettable materials, and disposal of microbial cultures.

    Filtration

    • Used to sterilize solutions that may be damaged by high temperatures or chemical agents.
    • Used for sterilizing heat-labile materials like sera, sugar solutions, antibiotics, and vitamin solutions.
    • Types of filters:
      • Earthenware filters (Candle filters)
      • Asbestos disc (Seitz) filters
      • Sintered glass filters
      • Membrane filters
      • Syringe filters
      • Air filters

    Earthenware Filters

    • Manufactured in different porosity grades.
    • Widely used for purifying water for industrial and drinking purposes.
    • Types:
      • Unglazed ceramic filters (e.g., Chamberland and Doulton filters)
      • Compressed diatomaceous earth filters (e.g., Berkefeld and Mandler filters)

    Asbestos Filters

    • Made of an asbestos (magnesium trisilicate) disc.
    • Available in different porosity grades.

    Sintered Glass Filters

    • Prepared by fusing finely powdered glass particles.
    • Available in different pore sizes.
    • Pore size is controlled by the particle size of the glass powder.

    Membrane Filters

    • Made of polymeric materials like cellulose nitrate, cellulose diacetate, polycarbonate, and polyester.
    • 0.22 µm and 0.45 µm filters commonly used.
    • Used for water analysis, bacterial counts in water, sterility testing, and solution preparation.

    Syringe Filters

    • Syringes with membrane filters of different pore sizes (0.22 and 0.45 µm) are available.
    • Fluid is forced through the membrane by pressing the syringe piston.

    Air Filters

    • Air can be sterilized using high-efficiency particulate air (HEPA) filters.
    • Used in laminar air flow systems in microbiology laboratories.
    • HEPA filters remove particles of 0.3 µm or larger.

    Radiation

    • Two types of radiation used for sterilization:
      • Non-ionizing radiation
      • Ionizing radiation

    Non-ionizing Radiation

    • Includes infrared and ultraviolet (UV) radiations.
    • Acts by denaturing bacterial protein and interfering with DNA replication (produces thymine dimers).
    • UV radiation used for disinfecting bacteriological laboratories, inoculation hoods, laminar flow systems, and operation theaters.

    Ionizing Radiation

    • Includes X-rays, Υ (gamma) rays, and cosmic rays.
    • Highly penetrative and lethal to all cells.
    • Damages DNA through various mechanisms.
    • Gamma radiations are used for sterilizing disposable items like plastic syringes, swabs, culture plates, cannulas, and catheters.
    • This is known as "cold sterilization" as there's no significant temperature increase.
    • Commercial plants use gamma radiation emitted from radioactive elements like Cobalt 60.
    • Advantages include speed, high penetrating power (sterilizing materials through outer packages and wrappings).

    Chemical Methods

    • Aldehydes

      • Formaldehyde: Lethal to bacteria, spores, viruses, and fungi due to its action on the aminogroup in protein molecules. Used in both liquid and vapor states. 10% aqueous solution is commonly used.
      • Glutaraldehyde: More active and less toxic than formaldehyde. Used as a 2% solution. Available commercially as 'cidex'. Used for sterilizing endoscopes, bronchoscopes, plastic endotracheal tubes, face masks, and rubber anesthetic tubes.

    • Alcohols

      • Ethanol and isopropanol are commonly used as skin antiseptics.
      • Denature bacterial proteins, rapidly killing them.
      • Not sporicidal or virucidal.
      • 60-70% alcohol is most effective.

    • Phenols

      • Lethal effect is due to cell membrane damage.
      • Phenol (1%) has bactericidal action.
      • Phenol derivatives like cresol, chlorhexidine, and hexachlorophene are used as antiseptics.
      • Cresols (Methylphenols): Lysol, a solution of cresols in soap, is used for sterilizing infected glassware and cleaning floors.
      • Chlorhexidine: Savlon (chlorhexidine and cetrimide) is widely used in wounds and pre-operative skin disinfection. Dettol (chlorhexilenol 4.8% + isopropyl alcohol + pine oil) has a good fungicidal activity. No action against spores and little activity against viruses.

    • Halogens

      • Chlorine and iodine are commonly used disinfectants.
      • Chlorine: Used in the form of bleaching powder and sodium hypochlorite. Used in water supplies, swimming pools, and food and dairy industries. Has bactericidal, fungicidal, virucidal, and sporicidal action. Bleaching powder and hypochlorite solutions are widely used.
      • Iodine: Used as a skin disinfectant in aqueous and alcoholic solutions, as tincture of iodine (2% iodine in a water-ethanol solution of potassium iodide). Bactericidal with moderate sporicidal action, also active against viruses. Compounds of iodine with surface active agents are known as iodophores (e.g., Betadine for wounds and Wescodyne for skin).

    • Vapor Phase Disinfectants

      • Used for sterilizing walls, ceilings, and heat-sensitive equipment.
      • Formaldehyde gas: Used for fumigation of heat-sensitive equipment (anesthetic machines and baby incubators), operation theatres, wards, and laboratories. Generated by adding 150 gm of KMnO4 to 280 ml of formalin for 1000 cubic feet of room volume. Sterilization is achieved by condensation of gas on exposed surfaces.
      • Ethylene oxide (ETO): Highly lethal to all microbes, including spores. Action is due to alkylation of amino, carboxyl, hydroxyl, and sulphydryl groups in protein molecules. It also reacts with DNA and RNA. Highly flammable and explosive at concentrations above 3%. Mixed with inert gases like CO2 to eliminate explosive tendency.
      • Uses: Sterilizing plastic and rubber articles, respirators, heart-lung machines, sutures, dental equipment, and clothing. Sterilization of disposable plastic syringes and Petri dishes. ETO has high penetrating power, sterilizing prepackaged materials.

    Scope of Infection Control

    • Standard precautions: Aiming at preventing the spread of infection.
    • Transmission-based precautions: Further measures to prevent infection transmission.

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    Explore the various methods of microbial control, including sterilization, disinfection, and antiseptics. This quiz covers both chemical and physical methods used to inhibit microbial growth, emphasizing the efficacy of heat and sunlight. Test your knowledge about how these techniques maintain safety in various environments.

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