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Questions and Answers
What is the primary purpose of an enrichment culture?
Which isolation technique is most appropriate when the desired microorganism is in higher abundance than others?
What is the main characteristic of the single-cell isolation technique?
Which statement about enrichment culture is incorrect?
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Which of the following factors does NOT typically influence enrichment cultures?
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What is the primary purpose of the membrane filter technique?
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Which step is NOT part of preparing pure cultures?
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What is the main objective of culture preservation?
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Which preservation method involves limiting the availability of oxygen?
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What is an advantage of overlaying cultures with mineral oil?
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What consideration is important when making periodic transfers to fresh media?
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Which of the following statements about preparing stock cultures is accurate?
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Which method is NOT associated with maintaining culture purity during preservation?
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Which type of culture media is primarily used for supporting a wide variety of microorganisms?
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What ingredient in Potato Dextrose Agar primarily helps in the enumeration of molds?
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Which of the following is an example of differential culture media?
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What is a characteristic function of selective media?
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Which of the following microorganisms is NOT typically associated with Potato Dextrose Agar?
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What purpose does using special reagents like pH indicators serve in differential media?
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Which of the following is considered a general purpose culture media?
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Which extract is derived from animal origin and is commonly used in culture media preparations?
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What is a pure culture?
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Which of the following describes the purpose of culture media?
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How are culture media classified according to physical state?
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What defines a synthetic culture medium?
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What is the main use of culture media in microbiology?
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What is the purpose of adding a solidifying agent to culture media?
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What is an example of a culture preservation technique?
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What characterizes complex culture media?
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Which isolation technique is primarily used for separating microorganisms based on their growth rate?
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Why are culture collections important in microbiology?
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What is the drying temperature required for samples grown on sterile paper disks?
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What is the primary limitation when drying samples on sterile disks?
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Which organization is known for maintaining authentic pure cultures of microorganisms?
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In which location is the National Collection of Type Cultures (NCTC) based?
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What is the primary function of culture collections like the ATCC?
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Which of the following is a characteristic typical of spore- and cyst-formers?
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Which of the following is NOT an example of a culture collection?
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What is the recommended practice after drying the disks containing microbial samples?
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Study Notes
Membrane Filter Technique
- Utilizes a sterile membrane filter designed to retain microorganisms in samples with low populations.
Preparation of Pure Cultures
- Steps for preparing pure cultures include isolation, transfer of desired colonies, purity verification (microscopic examination, re-streaking on agar, physiological and biochemical tests), and making stock cultures.
Culture Preservation
- Aim is to retain the viability of stock cultures over time while ensuring purity.
Culture Preservation Methods
- Periodic Transfer to Fresh Media: Involves transferring cultures regularly to maintain growth; essential considerations include time intervals, suitable medium, and storage temperature.
- Overlaying Cultures with Mineral Oil: Reduces oxygen availability, thereby lowering metabolic rates; simple to use, allows for growth removal under oil for fresh medium inoculation while preserving the initial culture.
Expected Learning Outcomes
- Knowledge of culture media types and their applications.
- Ability to compare different isolation techniques and their principles.
- Understanding basic culture preservation techniques.
- Awareness of the importance of culture collections and examples.
Definitions
- Pure Culture (Axenic Culture): Consists of a single microorganism species, originating from a single cell.
- Cultivation: The increase in the microorganism population through the provision of necessary nutritional and physical requirements.
- Nutrients: Extracellular substances essential for building protoplasm and energy generation.
- Culture Medium: Nutrient materials provided for the growth and cultivation of microorganisms in laboratory settings.
Uses of Culture Medium
- Facilitates growth and maintenance of microbial cultures.
- Promotes the production of specific compounds.
- Investigates microbial actions on medium components.
Types of Culture Media
-
By Physical State:
- Liquid (Broth): No solidifying agent.
- Semi-Solid: Contains 0.1 - 0.5% solidifying agent like agar or gelatin.
- Solid: Contains 1.5 - 2.0% solidifying agent.
-
By Chemical Composition:
- Synthetic: Chemically defined components.
- Complex: Contains undefined components, e.g., potato infusion, beef extract, yeast extract.
-
By Function or Purpose:
- General Purpose: Supports most species (e.g., Nutrient Agar, Potato Dextrose Agar).
- Differential Media: Distinguishes between bacteria using special reagents (e.g., Eosin Methylene Blue Agar).
- Enrichment Culture: Used for isolating specific microorganisms through nutrient and physical conditions.
Isolation Techniques
- Enrichment Culture: Selects microorganisms present in low numbers through appropriate nutrient conditions.
- Serial Dilution: Reduces concentration to isolate desired microorganisms when they are present at higher levels.
- Single-Cell Isolation Technique: Involves physically transferring a single microorganism to agar using a micropipette.
- Drying: Cultures grown on nutrient-saturated paper disks, dried, and stored aseptically, effective for spore and cyst-forming organisms.
Culture Collections
- Organizations maintain authentic pure cultures of microorganisms and supply type strains globally.
- Notable examples include:
- American Type Culture Collection (ATCC): Located in Maryland.
- National Collection of Type Cultures (NCTC): Based in London.
- Philippine National Collection of Microorganisms: Additional regional example.
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Description
Explore the Membrane Filter Technique designed for isolating microorganisms from low population samples. This quiz covers essential steps for preparing pure cultures, including isolation and verification of purity. Test your understanding of this vital microbiological method.
