Disinfection and Sterilization Concepts
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Questions and Answers

What is the main reason UV radiation is lethal to most microorganisms?

  • It alters their metabolic pathways.
  • It damages their DNA. (correct)
  • It induces rapid cell division.
  • It produces heat that destroys cell membranes.

What type of microorganisms can be removed from liquids using filtration?

  • All microorganisms
  • Cellular organisms excluding viruses (correct)
  • Viruses only
  • Only bacterial spores

What is the purpose of using high concentrations of salt or sugar in food preservation?

  • To improve nutritional value.
  • To facilitate enzymatic reactions.
  • To decrease water availability to microbes. (correct)
  • To enhance flavor and color.

Which of the following correctly describes a germicide applied to inanimate objects?

<p>Disinfectant (C)</p> Signup and view all the answers

How is the effectiveness of a germicide typically compared?

<p>By comparing its phenol coefficient. (C)</p> Signup and view all the answers

What does the zone of inhibition indicate in the disk diffusion method?

<p>Effectiveness of the germicide. (C)</p> Signup and view all the answers

Which term refers to chemicals that inhibit microbial growth?

<p>Germistats (D)</p> Signup and view all the answers

Which method is commonly used to dry products like proteins after they are frozen?

<p>Vacuum drying (A)</p> Signup and view all the answers

What characteristics are associated with Penicillin as an antibiotic?

<p>Bactericidal, broad-spectrum, minimal side effects (A)</p> Signup and view all the answers

Which sterilization method uses high temperature and pressure for its process?

<p>Moist heat (A)</p> Signup and view all the answers

What is the primary usage of filter sterilization?

<p>To remove microbial cells from heat-sensitive liquids (A)</p> Signup and view all the answers

Which antibiotic class is known to block protein synthesis?

<p>Tetracyclines (C)</p> Signup and view all the answers

Why are alcohol and bleach unsuitable for sterilizing growth media?

<p>They are toxic to microbial growth (B)</p> Signup and view all the answers

What type of organism is actively targeted by antihelminthics?

<p>Helminths (B)</p> Signup and view all the answers

Which statement best describes the characteristics of sulphonamides?

<p>Bacteriostatic, interfere with folic acid synthesis, broad-spectrum (C)</p> Signup and view all the answers

What is a significant requirement for culturing viruses in the laboratory?

<p>Living host cells (C)</p> Signup and view all the answers

What is the primary mechanism by which phenols and phenolics kill microbes?

<p>Denaturing vital cellular proteins (B)</p> Signup and view all the answers

Which of the following statements is true regarding the use of alcohols as germicides?

<p>They disrupt lipids in the cell membrane. (B)</p> Signup and view all the answers

Which class of germicides is characterized by their ability to inactivate proteins through reaction with sulphydryl groups?

<p>Heavy metals (A)</p> Signup and view all the answers

What is the role of surfactants in infection control?

<p>They emulsify oily materials to aid in washing away microbes. (C)</p> Signup and view all the answers

In the disk diffusion method, what does a larger zone of inhibition indicate?

<p>The bacterium is sensitive to the germicide. (B)</p> Signup and view all the answers

What is an example of an alkylating agent used as a germicide?

<p>Glutaraldehyde (B)</p> Signup and view all the answers

Which of the following germicides is primarily used as an antiseptic for wound cleaning?

<p>Hydrogen peroxide (A)</p> Signup and view all the answers

What primary function do halogens serve in germicidal applications?

<p>Oxidizing cellular components (C)</p> Signup and view all the answers

What distinguishes a defined medium from a complex medium?

<p>Defined mediums have a known composition, while complex mediums do not. (D)</p> Signup and view all the answers

Which method is NOT used to isolate a single microorganism into a pure culture?

<p>Inoculation loop method (B)</p> Signup and view all the answers

What type of medium allows growth of specific microorganisms while inhibiting others?

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

Which of the following statements about differential media is true?

<p>Differential media is used to isolate microorganisms by colony appearance. (D)</p> Signup and view all the answers

Which of the following factors does NOT influence the growth of microorganisms in culture?

<p>Ambient light levels (C)</p> Signup and view all the answers

What is the process of fixing microorganisms on a microscope slide primarily intended for?

<p>To allow staining to effectively visualize the organisms. (C)</p> Signup and view all the answers

What is a characteristic feature of a broth as a type of complex medium?

<p>It is a liquid medium that does not contain agar. (C)</p> Signup and view all the answers

In the pour plate method, what happens to the diluted sample before it is poured into the petri dish?

<p>It is mixed with agar and then poured. (C)</p> Signup and view all the answers

What is the primary goal of sterilization?

<p>To destroy all microbial life (A)</p> Signup and view all the answers

Which treatment is described as microbiostatic?

<p>Refrigeration of food items (D)</p> Signup and view all the answers

What differentiates disinfection from sterilization?

<p>Disinfection reduces pathogens to a safe level (B)</p> Signup and view all the answers

Which of the following is an example of a microbiocidal treatment?

<p>Boiling water for an extended period (D)</p> Signup and view all the answers

What is the correct autoclave condition for effective sterilization?

<p>121°C for 15 minutes at 15 lbs pressure (A)</p> Signup and view all the answers

Which of the following statements about cold treatment is true?

<p>Cold is a microbiostatic method. (C)</p> Signup and view all the answers

What is the temperature range used in dry heat sterilization?

<p>160°C – 180°C for 1 hour (A)</p> Signup and view all the answers

What is the role of antiseptics?

<p>To kill microorganisms on living tissue (C)</p> Signup and view all the answers

Flashcards

Sterilization

A process that eliminates all forms of microbial life, including highly resistant bacterial endospores, viruses, and prions.

Disinfection

A treatment designed to reduce the number of potentially harmful microorganisms to a level considered safe for public health, often practiced on inanimate objects.

Antiseptics

A type of disinfection that involves the use of chemical agents that are safe for application to living tissues, targeting microbial populations on the skin or wounds.

Microbiocidal Treatments

Treatments that eliminate all types of microorganisms, effectively killing them entirely.

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Microbiostatic Treatments

Treatments that inhibit or pause the growth and reproduction of microorganisms without directly killing them. When the treatment is removed, the microorganisms can resume their growth.

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Heat Sterilization

A type of physical sterilization method that uses high temperatures to destroy microorganisms. It can be applied through dry or moist heat methods.

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Autoclaving

A type of heat sterilization method that utilizes high-pressure, saturated steam to eliminate all forms of microbial life, notably including resistant endospores.

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Cold Treatment

A physical method of microbial control that uses low temperatures to inhibit microbial growth. This method is commonly used to extend the shelf life of perishable foods.

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UV radiation

UV radiation (10-400 nm) is lethal to most microorganisms as it damages their DNA.

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Filtration

A process of removing microorganisms from liquids by passing them through a filter with pores smaller than the microbes.

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Drying

Removing water from a substance, often used in food preservation. It can be done by evaporation or freeze-drying.

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Osmotic strength

High concentrations of salt or sugar solutions are used to preserve foods by reducing water available to microbes.

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Chemotherapeutic agents

Chemicals used to treat diseases, including antibiotics.

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Germicides

Chemicals that kill microorganisms.

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Germistats

Chemicals that inhibit (slow down) the growth of microorganisms.

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Phenol coefficient

A test to compare the effectiveness of a disinfectant to phenol, a traditional disinfectant.

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Disk Diffusion Method

A method used to assess the effectiveness of antimicrobial agents by measuring the size of the zone around a disk on an agar plate where bacterial growth is inhibited. This zone reflects the sensitivity of the bacterium to the specific agent.

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Antimicrobial Chemotherapy

Chemicals that kill or inhibit the growth of microorganisms, used to control bacterial growth in a host, i.e. to treat infection.

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Alcohols (Germicides)

Agents that work by destroying the lipid membrane of bacteria, leading to cell death. They are commonly used for skin disinfection.

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Phenols & Phenolics (Germicides)

Substances that kill by disrupting the proteins crucial for bacterial function, often by breaking down their structure.

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Halogens & Hydrogen Peroxide (Germicides)

Oxidizing agents that kill microbes by disrupting cellular processes. Chlorine is used for disinfection, while Iodine acts as an antiseptic.

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Heavy Metals (Germicides)

Chemicals that bind to proteins in bacterial cells, disabling them and leading to cell death. Examples include Mercurochrome and silver nitrate.

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Surfactants (Germicides)

Compounds like soaps that have both water-loving and oil-loving parts. They emulsify oily substances making them easier to wash away, helping to control the spread of infections.

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Alkylating Agents (Germicides)

Chemicals that attach to proteins, altering their structure and preventing them from functioning, effectively disabling bacterial cells. Examples include glutaraldehyde and formaldehyde.

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Defined medium

A growth medium prepared from pure chemicals with a known composition.

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Complex medium

A growth medium made from extracts of natural materials like beef or yeast, with an unknown exact composition.

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Broth

A liquid complex medium.

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Selective media

A growth medium that favors the growth of specific microorganisms.

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Differential media

A growth medium that allows for the identification of microorganisms based on their colony appearance.

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Isolation of a microorganism

A method of isolating a single microorganism by separating it from other cells and providing nutrients for its survival.

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Streak plate

A technique for spreading microorganisms on a solid medium to isolate individual colonies.

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Pour plate

A technique for isolating microorganisms by diluting a sample and pouring it onto a solid medium before allowing growth.

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Antibiotics

Antimicrobial drugs that target and kill bacteria. They work by interfering with essential bacterial processes like cell wall synthesis, protein synthesis, or DNA replication.

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Broad-spectrum antibiotics

Antimicrobial drugs that are effective against a wide range of bacteria, including both Gram-positive and Gram-negative bacteria.

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Narrow-spectrum antibiotics

Antimicrobial drugs that are only effective against specific types of bacteria, often categorized as Gram-positive or Gram-negative.

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Penicillins

A class of antibiotics that interfere with the synthesis of bacterial cell walls, leading to bacterial cell death. They are effective against a wide range of bacteria, particularly Gram-positive bacteria.

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Sulphonamides

A class of antibiotics that block the synthesis of folic acid, an essential nutrient for bacterial growth. They are effective against a wide range of bacteria, particularly Gram-negative bacteria.

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Filtration sterilization

A type of sterilization that involves the use of filters with very small pores to physically remove microorganisms from liquids or gases. This method is suitable for heat-sensitive materials.

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Study Notes

Disinfection and Sterilization

  • Microorganisms cause illness and food spoilage.
  • Effective microbial control requires understanding how treatments affect microbial populations.
  • Treatments may kill cells or slow growth without killing them.

Important Terms

  • Sterilization: Destroys all microbial life.
  • Disinfection (Sanitizing): Reduces pathogen numbers to a level where they pose no disease risk.
  • Antiseptics: Kill microorganisms on living tissue.
  • Microbiocidal treatments: Kill all microorganisms.
  • Microbiostatic treatments: Inhibit microbial growth. Refrigeration serves as an example.

Physical Treatments

  • Heat: Effective for heat-insensitive materials.
    • Dry heat (flames, ovens).
    • Moist heat (boiling, autoclaving).
    • Autoclaving effectively destroys endospores.
  • Dry Heat Methods
    • Hot air oven (160°C–180°C for 1 hour)
    • Flaming (direct exposure)
    • Red heat (holding inoculating loops, etc.)
    • Incineration (destruction by burning)
    • Infra-red radiation (using infra-red rays directed from an electrically heated element onto the objects)
  • Hot air sterilizer: A device used for dry heat sterilization.
  • Moist Heat Methods
    • Boiling ( < 100°C)
    • Steam (~100°C)
    • Steam under pressure (autoclave, >100°C)
  • Autoclave: Uses saturated steam under pressure (121°C for 15 minutes at 15 lbs pressure). Destroys microorganisms, including spores. Used for sterilizing surgical supplies and bacteriological culture media.
  • Cold: Microbiostatic. Low temperatures slow microbial growth. Refrigeration is an example preserving food.
  • Radiation:
    • UV radiation (10nm to 400nm) damages DNA, killing most microorganisms.
    • Germicidal lamps use UV to kill microorganisms on surfaces.
  • Filtration: Removes microorganisms (except viruses) from liquids. Effective for heat-sensitive substances like vitamins and antibiotics.
  • Drying: Removes water. Evaporation is common in food industry. Freeze-drying (freezing, then vacuum drying) preserves proteins and blood products.
  • Osmotic strength: High salt or sugar solutions decrease the amount of water available to microbes, causing plasmolysis. Used to preserve foods.

Chemical Treatments

  • Chemotherapeutic agents: Chemicals used to treat diseases, including antibiotics.
  • Germicides: Chemicals that kill microorganisms.
  • Disinfectants: Germicides used on inanimate objects.
  • Antiseptics: Germicides applied to living tissues.
  • Germistats: Chemicals that inhibit microbial growth.
  • Testing germicides: Comparing effectiveness to phenol (a traditional germicide) via phenol coefficient, disc diffusion method.

Classes of Germicides

  • Phenols and Phenolics: Denature cellular proteins, often act on lipid cytoplasmic membranes. Example: Lysol.
  • Alcohols: Disrupt lipids and denature proteins. Examples: Ethanol, isopropanol. Note: ineffective against endospores.
  • Halogens and Hydrogen Peroxide: Oxidising agents. Examples: Iodine (antiseptic), chlorine (disinfectant, in bleach/pools), hydrogen peroxide (antiseptic for wounds).
  • Heavy Metals: React with sulphydryl groups of proteins, inactivating and killing the cell. Examples: Mercurochrome, silver nitrate.
  • Surfactants: Compounds with hydrophobic and hydrophilic parts that emulsify oily materials. Examples: soaps.
  • Alkylating Agents: Attach short carbon chains to proteins, inactivating them. Examples: Glutaraldehyde, formaldehyde.

Antimicrobial Chemotherapy

  • Chemicals for microbial growth control in a host (treat infection). Subclasses: antibiotics (against bacteria), antivirals (viruses), antifungals (fungi), antihelminthics (helminths), antiprotozoals (protozoa).

Some Main Classes of Antibiotics

  • Penicillin: Bactericidal, broad-spectrum, effective on Gram-positive bacteria, minimal side effects.
  • Cephalosporins: Similar in structure to penicillins.
  • Sulphonamides: Interferes with folic acid synthesis, broad-spectrum, bacteriostatic, effective against Gram-negative bacteria.
  • Tetracyclines: Broad-spectrum, blocks protein synthesis.
  • Quinolones: Blocks DNA replication, broad-spectrum.

Aseptic Techniques

  • Pure cultures (one type of organism) needed for experiments.
  • Provides appropriate conditions for growth and multiplication in the laboratory.

Media for Growth

  • Growth Medium: A medium suitable for culturing a particular organism depends on nutritional requirements.
  • Types of Growth Media:
    • Defined Media: Prepared from pure chemicals, with known composition.
    • Complex Media: Made from natural extracts (e.g., beef, yeast, blood) with unknown composition. Liquid media are called broth. Solid media use agar.
    • Selective Media: Favours the growth of specific microorganisms.
    • Differential Media: Isolates microorganisms based on colony appearance. Example: Blood agar plate for Streptococcus spp.

Isolation of Microorganisms

  • Separates a single cell, gives it nutrients for survival, from other cells in population.
  • Methods:
    • Streak plate: Distributes microorganisms across media.
    • Pour plate: Diluted sample mixed with melted agar and poured into Petri dish.
    • Spread plate: Diluted sample spread evenly on media using a sterile rod.
  • Examination methods: Microscopic examination and staining techniques
    • Stains are most effective after organisms are killed and attached to the slide.

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Disinfection & Sterilization PDF

Description

Explore the essential concepts of disinfection and sterilization in preventing illness and food spoilage. This quiz covers key terms and physical treatments, including sterilization methods like heat and microbiocidal treatments. Test your knowledge on how these processes affect microbial populations.

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