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Questions and Answers
What is the main reason UV radiation is lethal to most microorganisms?
What is the main reason UV radiation is lethal to most microorganisms?
What type of microorganisms can be removed from liquids using filtration?
What type of microorganisms can be removed from liquids using filtration?
What is the purpose of using high concentrations of salt or sugar in food preservation?
What is the purpose of using high concentrations of salt or sugar in food preservation?
Which of the following correctly describes a germicide applied to inanimate objects?
Which of the following correctly describes a germicide applied to inanimate objects?
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How is the effectiveness of a germicide typically compared?
How is the effectiveness of a germicide typically compared?
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What does the zone of inhibition indicate in the disk diffusion method?
What does the zone of inhibition indicate in the disk diffusion method?
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Which term refers to chemicals that inhibit microbial growth?
Which term refers to chemicals that inhibit microbial growth?
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Which method is commonly used to dry products like proteins after they are frozen?
Which method is commonly used to dry products like proteins after they are frozen?
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What characteristics are associated with Penicillin as an antibiotic?
What characteristics are associated with Penicillin as an antibiotic?
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Which sterilization method uses high temperature and pressure for its process?
Which sterilization method uses high temperature and pressure for its process?
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What is the primary usage of filter sterilization?
What is the primary usage of filter sterilization?
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Which antibiotic class is known to block protein synthesis?
Which antibiotic class is known to block protein synthesis?
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Why are alcohol and bleach unsuitable for sterilizing growth media?
Why are alcohol and bleach unsuitable for sterilizing growth media?
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What type of organism is actively targeted by antihelminthics?
What type of organism is actively targeted by antihelminthics?
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Which statement best describes the characteristics of sulphonamides?
Which statement best describes the characteristics of sulphonamides?
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What is a significant requirement for culturing viruses in the laboratory?
What is a significant requirement for culturing viruses in the laboratory?
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What is the primary mechanism by which phenols and phenolics kill microbes?
What is the primary mechanism by which phenols and phenolics kill microbes?
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Which of the following statements is true regarding the use of alcohols as germicides?
Which of the following statements is true regarding the use of alcohols as germicides?
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Which class of germicides is characterized by their ability to inactivate proteins through reaction with sulphydryl groups?
Which class of germicides is characterized by their ability to inactivate proteins through reaction with sulphydryl groups?
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What is the role of surfactants in infection control?
What is the role of surfactants in infection control?
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In the disk diffusion method, what does a larger zone of inhibition indicate?
In the disk diffusion method, what does a larger zone of inhibition indicate?
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What is an example of an alkylating agent used as a germicide?
What is an example of an alkylating agent used as a germicide?
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Which of the following germicides is primarily used as an antiseptic for wound cleaning?
Which of the following germicides is primarily used as an antiseptic for wound cleaning?
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What primary function do halogens serve in germicidal applications?
What primary function do halogens serve in germicidal applications?
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What distinguishes a defined medium from a complex medium?
What distinguishes a defined medium from a complex medium?
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Which method is NOT used to isolate a single microorganism into a pure culture?
Which method is NOT used to isolate a single microorganism into a pure culture?
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What type of medium allows growth of specific microorganisms while inhibiting others?
What type of medium allows growth of specific microorganisms while inhibiting others?
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Which of the following statements about differential media is true?
Which of the following statements about differential media is true?
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Which of the following factors does NOT influence the growth of microorganisms in culture?
Which of the following factors does NOT influence the growth of microorganisms in culture?
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What is the process of fixing microorganisms on a microscope slide primarily intended for?
What is the process of fixing microorganisms on a microscope slide primarily intended for?
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What is a characteristic feature of a broth as a type of complex medium?
What is a characteristic feature of a broth as a type of complex medium?
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In the pour plate method, what happens to the diluted sample before it is poured into the petri dish?
In the pour plate method, what happens to the diluted sample before it is poured into the petri dish?
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What is the primary goal of sterilization?
What is the primary goal of sterilization?
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Which treatment is described as microbiostatic?
Which treatment is described as microbiostatic?
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What differentiates disinfection from sterilization?
What differentiates disinfection from sterilization?
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Which of the following is an example of a microbiocidal treatment?
Which of the following is an example of a microbiocidal treatment?
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What is the correct autoclave condition for effective sterilization?
What is the correct autoclave condition for effective sterilization?
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Which of the following statements about cold treatment is true?
Which of the following statements about cold treatment is true?
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What is the temperature range used in dry heat sterilization?
What is the temperature range used in dry heat sterilization?
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What is the role of antiseptics?
What is the role of antiseptics?
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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
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Heat: Effective for heat-insensitive materials.
- Dry heat (flames, ovens).
- Moist heat (boiling, autoclaving).
- Autoclaving effectively destroys endospores.
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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.
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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.
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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.
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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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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.
