Membrane Filter Technique Overview

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Questions and Answers

What is the primary purpose of an enrichment culture?

  • To isolate specific microorganisms using broad-spectrum antibiotics
  • To promote the growth of all types of microorganisms equally
  • To isolate microorganisms that grow slowly and are present in small numbers (correct)
  • To enhance the growth of microorganisms in the presence of toxins

Which isolation technique is most appropriate when the desired microorganism is in higher abundance than others?

  • Serial dilution (correct)
  • Single-cell isolation
  • Microscopic examination
  • Enrichment culture

What is the main characteristic of the single-cell isolation technique?

  • It requires the application of chemical agents to immobilize cells
  • It involves the use of heat to kill unwanted microorganisms
  • It randomly samples multiple cells from a culture medium
  • It physically picks a single cell using a micropipette or microprobe (correct)

Which statement about enrichment culture is incorrect?

<p>It aims to enhance the growth of dominant microorganisms (B)</p> Signup and view all the answers

Which of the following factors does NOT typically influence enrichment cultures?

<p>Visibility of the colonies under a microscope (D)</p> Signup and view all the answers

What is the primary purpose of the membrane filter technique?

<p>To retain microorganisms. (C)</p> Signup and view all the answers

Which step is NOT part of preparing pure cultures?

<p>Preparation of stock solutions. (B)</p> Signup and view all the answers

What is the main objective of culture preservation?

<p>To retain viability and purity of stock cultures. (D)</p> Signup and view all the answers

Which preservation method involves limiting the availability of oxygen?

<p>Overlaying cultures with mineral oil. (A)</p> Signup and view all the answers

What is an advantage of overlaying cultures with mineral oil?

<p>It helps in the removal of growth to inoculate fresh medium. (A)</p> Signup and view all the answers

What consideration is important when making periodic transfers to fresh media?

<p>Time interval of transfers. (D)</p> Signup and view all the answers

Which of the following statements about preparing stock cultures is accurate?

<p>Verification of purity involves using physiological and biochemical tests. (C)</p> Signup and view all the answers

Which method is NOT associated with maintaining culture purity during preservation?

<p>Regularly displacing cultures with contaminants. (B)</p> Signup and view all the answers

Which type of culture media is primarily used for supporting a wide variety of microorganisms?

<p>General Purpose Media (D)</p> Signup and view all the answers

What ingredient in Potato Dextrose Agar primarily helps in the enumeration of molds?

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

Which of the following is an example of differential culture media?

<p>Eosin Methylene Blue Agar (A)</p> Signup and view all the answers

What is a characteristic function of selective media?

<p>Inhibits the growth of certain organisms (C)</p> Signup and view all the answers

Which of the following microorganisms is NOT typically associated with Potato Dextrose Agar?

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

What purpose does using special reagents like pH indicators serve in differential media?

<p>To distinguish one type of bacteria from another (D)</p> Signup and view all the answers

Which of the following is considered a general purpose culture media?

<p>Nutrient Agar (A)</p> Signup and view all the answers

Which extract is derived from animal origin and is commonly used in culture media preparations?

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

What is a pure culture?

<p>A culture containing a single species of microorganism (C)</p> Signup and view all the answers

Which of the following describes the purpose of culture media?

<p>To provide nutritional and physical requirements for microorganisms (D)</p> Signup and view all the answers

How are culture media classified according to physical state?

<p>Solid, Semi-solid, and Liquid (B)</p> Signup and view all the answers

What defines a synthetic culture medium?

<p>Contains all components that are chemically defined (A)</p> Signup and view all the answers

What is the main use of culture media in microbiology?

<p>For growth and maintenance of microbial cultures (D)</p> Signup and view all the answers

What is the purpose of adding a solidifying agent to culture media?

<p>To provide a solid surface for growth of microorganisms (A)</p> Signup and view all the answers

What is an example of a culture preservation technique?

<p>Cryopreservation of microbial strains (C)</p> Signup and view all the answers

What characterizes complex culture media?

<p>Nutrient sources are natural and not fully defined (D)</p> Signup and view all the answers

Which isolation technique is primarily used for separating microorganisms based on their growth rate?

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

Why are culture collections important in microbiology?

<p>They provide a source of organisms for study and identification (A)</p> Signup and view all the answers

What is the drying temperature required for samples grown on sterile paper disks?

<p>45°C (A)</p> Signup and view all the answers

What is the primary limitation when drying samples on sterile disks?

<p>Not suitable for spore- and cyst-forming organisms (A)</p> Signup and view all the answers

Which organization is known for maintaining authentic pure cultures of microorganisms?

<p>American Type Culture Collection (ATCC) (B)</p> Signup and view all the answers

In which location is the National Collection of Type Cultures (NCTC) based?

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

What is the primary function of culture collections like the ATCC?

<p>To preserve and maintain authentic cultures (B)</p> Signup and view all the answers

Which of the following is a characteristic typical of spore- and cyst-formers?

<p>They can withstand extreme environmental conditions. (B)</p> Signup and view all the answers

Which of the following is NOT an example of a culture collection?

<p>National Institute of Health Cultures (C)</p> Signup and view all the answers

What is the recommended practice after drying the disks containing microbial samples?

<p>Store them aseptically (B)</p> Signup and view all the answers

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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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