Microbial Sterilization Methods Quiz
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Questions and Answers

What is the main mechanism by which dry heat sterilization kills microorganisms?

  • Oxidation (correct)
  • Desiccation
  • Denaturation of proteins
  • Freezing

    • Which sterilization method uses Cobalt-60 radioisotope?

  • Ionizing radiation (correct)
  • Filtration
  • Nonionizing radiation
  • Hot-air sterilization

    • What is the pore size range typically used for membrane filters to remove bacteria?

  • 1.0 – 5.0 µm
  • 0.01 – 0.1 µm
  • 0.2 – 0.4 µm (correct)
  • 0.5 – 1.0 µm

    • Which method is used as 'cold pasteurization' for food?

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

    What is one effect of nonionizing radiation, such as UV light, on actively dividing cells?

    <p>Formation of thymine dimers</p> Signup and view all the answers

    What is the main disadvantage of using microwaves for sterilization?

    <p>Heats solid food unevenly</p> Signup and view all the answers

    Which sterilization technique uses temperature of 170˚C for effective treatment?

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

    What effect does osmotic pressure have on microorganisms?

    <p>Induces plasmolysis</p> Signup and view all the answers

    What is the primary objective of sterilization?

    <p>To kill all microbial life</p> Signup and view all the answers

    Which of the following methods is commonly used for commercial sterilization?

    <p>High heat treatment</p> Signup and view all the answers

    What best describes pasteurization?

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

    What is the primary difference between a disinfectant and an antiseptic?

    <p>Disinfectants are used on surfaces, while antiseptics are used on living tissues.</p> Signup and view all the answers

    The microbial death curve illustrates which of the following?

    <p>The constant rate of microbial death over time</p> Signup and view all the answers

    Which sterilization method is specifically effective for plastic labware?

    <p>Radiation sterilization</p> Signup and view all the answers

    What is a key disadvantage of using dry heat sterilization compared to moist heat methods?

    <p>All of the above.</p> Signup and view all the answers

    What is the primary action of a biocide?

    <p>To kill all bacterial cells</p> Signup and view all the answers

    What is the thermal death point (TDP)?

    <p>The lowest temperature at which all cells in a culture are killed in 10 minutes.</p> Signup and view all the answers

    Which of the following statements about autoclaving is correct?

    <p>Steam must contact the material directly to be effective.</p> Signup and view all the answers

    What is the primary purpose of pasteurization?

    <p>To significantly reduce spoilage and pathogenic organisms.</p> Signup and view all the answers

    Which method effectively eliminates prions during sterilization?

    <p>132°C for 4.5 hours.</p> Signup and view all the answers

    What does the Decimal Reduction Time (DRT) indicate?

    <p>Time required to kill 90% of a population at a specific temperature.</p> Signup and view all the answers

    Which pasteurization method achieves sterilization?

    <p>Ultra High Temperature (UHT) at 140°C for less than 1 second.</p> Signup and view all the answers

    Which of the following is NOT an action of microbial control agents?

    <p>Alteration of lipid mobility.</p> Signup and view all the answers

    How does the presence of organic matter affect heat treatments?

    <p>It may interfere with heat treatments and chemical controls.</p> Signup and view all the answers

    What is the lowest temperature at which all cells in a culture are killed in 10 minutes?

    <p>Thermal death point</p> Signup and view all the answers

    Pasteurization is a process that sterilizes a substance.

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

    What is the name of the process used to kill bacteria with high pressure in liquids?

    <p>High pressure processing or pascalization</p> Signup and view all the answers

    Give two examples of bisphenols used as disinfectants.

    <p>Hexachlorophene and triclosan</p> Signup and view all the answers

    Alcohols are effective against all types of microorganisms, including spores.

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

    What is the term for the action of heavy metals against microorganisms?

    <p>Oligodynamic action</p> Signup and view all the answers

    The use-dilution test is used to determine the effectiveness of antiseptics.

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

    Plasma sterilization is most suitable for sterilizing porous materials.

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

    What are the main types of microbial control agents?

    <p>Physical and chemical</p> Signup and view all the answers

    Identify two factors that are essential for effective disinfection.

    <p>Concentration and time</p> Signup and view all the answers

    Match the antimicrobial agent to its associated effect.

    <p>Aldehydes = Disrupt cell membranes Halogens = Oxidation Heavy metals = Oligodynamic action Alcohols = Denature proteins Surface-active agents = Denaturation and disruption of cell membranes Plasma = Free radicals Hydrogen peroxide = Inactivate proteins and DNA UV light = Thymine dimers</p> Signup and view all the answers

    Which group of microbes thrives at temperatures above 80°C?

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

    What impact does a hypertonic environment have on microbial cells?

    <p>Causes plasmolysis</p> Signup and view all the answers

    What are halophiles specifically adapted to thrive in?

    <p>High salt concentrations</p> Signup and view all the answers

    Which of the following elements is most abundant in the dry weight of microbial cells?

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

    What term is used to describe the time taken for the population of bacteria to double?

    <p>Generation time</p> Signup and view all the answers

    Which media type provides all the chemical requirements for microbial growth in known quantities?

    <p>Chemically defined media</p> Signup and view all the answers

    Which method is commonly used to isolate pure cultures of bacteria?

    <p>Streak plating</p> Signup and view all the answers

    How do aerobes typically protect themselves from toxic forms of oxygen?

    <p>Generating superoxide dismutase</p> Signup and view all the answers

    What phase of bacterial growth is characterized by the maximum rate of cell division?

    <p>Exponential phase</p> Signup and view all the answers

    Which method is commonly used for counting viable bacterial cells?

    <p>Plate count</p> Signup and view all the answers

    What does turbidity indicate when measuring microbial growth?

    <p>Cell number</p> Signup and view all the answers

    What is a disadvantage of using direct microscopic counts for microbial growth measurement?

    <p>It cannot distinguish between living and dead cells.</p> Signup and view all the answers

    Which of the following is NOT a direct method of measuring microbial growth?

    <p>Turbidity measurements</p> Signup and view all the answers

    What does the lag phase in bacterial growth represent?

    <p>Adaptation to the new environment</p> Signup and view all the answers

    Which measurement method allows for estimating microbial populations based on metabolic activity?

    <p>Indirect measurement</p> Signup and view all the answers

    What is the primary purpose of differential media in microbiology?

    <p>To change in a recognizable manner for the identification of specific microbes</p> Signup and view all the answers

    Which of the following techniques is essential for obtaining pure cultures?

    <p>Streak-plate method</p> Signup and view all the answers

    Which phase of bacterial growth is characterized by the balance between cell division and cell death?

    <p>Stationary phase</p> Signup and view all the answers

    Which method allows for the selective growth of phenol-degrading bacteria from a mixed culture?

    <p>Enrichment culture</p> Signup and view all the answers

    What is the generation time of E. coli under optimal growth conditions?

    <p>20 minutes</p> Signup and view all the answers

    How can bacterial cultures be preserved for several years?

    <p>By lyophilization or deep-freezing</p> Signup and view all the answers

    What does a colony represent in microbiological terms?

    <p>A population arising from a single cell or spore</p> Signup and view all the answers

    What temperature range is typical for deep-freezing bacterial cultures?

    <p>-50° to -95°C</p> Signup and view all the answers

    Which of the following statements about binary fission is correct?

    <p>It results in exponential growth of bacteria</p> Signup and view all the answers

    What role do trace elements play in microbial growth?

    <p>They serve as cofactors for enzymatic reactions.</p> Signup and view all the answers

    Which type of medium is specifically known for having all its chemical components defined?

    <p>Chemically defined media</p> Signup and view all the answers

    What is a characteristic feature of biofilms?

    <p>They are sheltered from harmful factors.</p> Signup and view all the answers

    What chemical is used in anaerobic culture methods to remove oxygen?

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

    What defines a capnophile?

    <p>A microorganism that requires high levels of carbon dioxide.</p> Signup and view all the answers

    What temperature range allows agar to solidify?

    <p>40-60°C</p> Signup and view all the answers

    Which of the following best describes how biofilms form?

    <p>By attachment of planktonic bacteria to surfaces.</p> Signup and view all the answers

    What form of oxygen can harm microorganisms by causing oxidative damage?

    <p>Superoxide free radicals</p> Signup and view all the answers

    What type of culture medium selectively suppresses the growth of undesired microorganisms?

    <p>Selective medium</p> Signup and view all the answers

    What is the initial step in the formation of biofilms?

    <p>Environmental attachment</p> Signup and view all the answers

    Study Notes

    Chapter 7: Control of Microbial Growth

    • Definitions:

      • Sterilization: Removal of all microbial life.
      • Disinfection: Reduction in the number of pathogenic microorganisms; destroys harmful microorganisms but not all.
      • Antisepsis: Removal of pathogens from living tissue.
      • Sanitization: Reduction in microbial numbers to a safe level (e.g., eating utensils).
      • Biocide/Germicide: Agents that kill microorganisms.
      • Bacteriostasis: Inhibition of microbial growth.
      • Asepsis: Absence of significant contamination.
      • Sepsis: Microbial contamination.
      • Nosocomial: Infections acquired in hospitals.
      • Commercial sterilization: Method of sterilization used for food products. The goal is killing C. botulinum endospores.
      • Bacteriostatic: Inhibits bacterial reproduction.
      • Bactericidal: Kills bacteria.
      • Fungicide/Sporicide/Germicide/Biocide: Agents that kill fungi/bacterial spores/microbes/living things.

    • Microbial Death Curve: The graph shows the constant rate of microbial death when exposed to heat or chemicals. Plotting this logarithmically shows microbial death constant as a straight line.

      • One log decrease = 90% population killed.

    • Factors Affecting Microbial Control Effectiveness:

      • Microbial population size.
      • Microbial characteristics (species, life cycle: endospores are more resistant).
      • Environmental conditions (temperature, organic matter, degree of contact).

    • Actions of Microbial Control Agents:

      • Alteration of membrane permeability.
      • Damage to proteins.
      • Damage to nucleic acids.

    • Physical Methods of Microbial Control:

      • Heat:
        • Moist Heat Sterilization (autoclaving):
          • Steam under pressure.
          • Most reliable sterilization method.
          • Steam must directly contact materials.
          • Normal autoclave conditions: 121.5°C for 15 minutes.
          • Prion destruction: 132°C for 4.5 hours.
          • Disadvantages: Limitations of the autoclave (e.g., can't use heat-sensitive items, care required).
        • Pasteurization:
          • Classic holding method: 63°C for 30 minutes.
          • Flash pasteurization (HTST): 72°C for 15 seconds.
          • Ultra High Temperature (UHT): 140°C for <1 second.
      • Dry Heat Sterilization: Incineration of carcasses, flaming of loops, hot air sterilization.
      • Filtration: HEPA filters for air. Membrane filters for fluids.
      • Low Temperature: Slows enzymatic reactions. Freezing forms ice crystals damaging microbial cells. Refrigeration and lyophilization.
      • High Pressure: Denatures bacterial proteins and preserves flavor.
      • Desiccation: Prevents metabolism.
      • Osmotic Pressure: Causes plasmolysis.
      • Ionizing Radiation:
        • X-rays, gamma rays, electron beams.
        • Dislodge electrons from atoms, producing free radicals.
        • Frequently used Cobalt-60 radioisotope and used to sterilize heat-sensitive materials (drugs, vitamins, herbs, suture materials).
      • Nonionizing Radiation (UV light):
        • Most effective wavelength ~260 nm.
        • Causes thymine dimers.
        • Actively dividing organisms are more sensitive.
        • Useful to limit contamination at a close range (e.g., germicidal lamps).
      • Nonionizing Radiation (Microwave):
        • Wavelength of 1 mm-1m.
        • Water quickly absorbs energy --> heats unevenly in solids.

    • Chemical Methods of Microbial Control:

      • Use-dilution test:
        • Metal rings dipped in bacteria are dried
        • Dried cultures are placed in disinfectant for 10 mins at 20°C.
        • Rings transferred to culture media to see if surviving bacteria.
      • Disk-diffusion method:
        • Disk soaked in chemical placed on inoculated agar plate.
        • In an inoculated agar plate, a zone of inhibition indicates the effectiveness of the chemical's action.
      • Phenol/Carbolic acid: Historic importance.
      • Phenolics(Cresols, Lysol): Disinfectants.
      • Bisphenols (Hexachlorophene, Triclosan): Disrupt plasma membranes.
      • Halogens (Chlorine, Iodine): Disinfectants/Antiseptics. Chlorine is a strong oxidizing agent used in bleaching and disinfecting (broad spectrum), while iodine is a more reactive agent used in wound antiseptics.
      • Alcohols (Ethyl, Isopropyl): Denature proteins, dissolve lipids; ineffective against spores/viruses/fungi. Easy deactivated by organic debris.
      • Heavy Metals (Mercury, Copper, Silver, Zinc): Oligodynamic action. Toxic to microorganisms; bind to sulfhydryl groups.
      • Surface-active agents (Soaps, Detergents): Mechanical removal and wetting. Cationic detergents (quats) are highly bactericidal.
      • Aldehydes (Formaldehyde, Glutaraldehyde): Alkylating agents. Used as sterilants for delicate materials.
      • Hydrogen Peroxide: An oxidizing agent, good for inanimate objects. Inactivated by catalase and not good for open wounds.
      • Chemical Food Preservatives (Sulfur Dioxide, Organic Acids): Inhibit metabolism of bacteria.

    • Plasma: Luminous gas with free radicals destroying microbes, used on instruments/hands.

    • Microbial Characteristics and Resistance:

      • Prions are the most resistant.
      • Endospores of bacteria are highly resistant.
      • Mycobacteria, cysts of protozoa are quite resistant.
      • Gram-negative bacteria are fairly resistant.
      • Fungi (spores) and viruses (without envelopes) are often resistant. Gram-positive bacteria. Viruses with lipid envelopes are the least resistant.

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    Description

    Test your knowledge on various sterilization techniques and their mechanisms. This quiz covers dry heat sterilization, radiation methods, and the effects of different sterilization processes on microorganisms. Ideal for students studying microbiology or related fields.

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