AmB 361 2025_Phoenix

Introduction to Culture Media

Definition

  • Mixtures of materials designed to support the metabolic processes of microorganisms in vitro.

  • Chemoheterotrophs are the primary microorganisms of interest in clinical laboratories.

Essential Nutrients for Growth

Carbon

  • Critical for synthesizing organic compounds.

  • Sourced from carbohydrates and protein breakdown products.

Nitrogen

  • Essential for protein and nucleic acid synthesis.

  • Can be derived from proteins; some prokaryotes fix atmospheric nitrogen.

Minerals

  • Vital minerals include sulfur, phosphorus, iron, calcium, magnesium, iodine, manganese, and copper.

  • Specific roles:

    • Sulfur: Amino acids

    • Phosphorus: Nucleic acids and phospholipids

    • Iron/Copper: Prosthetic groups in enzymes

  • Electrolytes like NaCl maintain cellular functions.

Water

  • Essential for metabolism and hydrolysis reactions.

  • Affects tonicity of media.

Buffers

  • Maintain pH stability in culture media.

Types of Culture Media

Medium Classification

  • Defined/Synthetic Media: All ingredients known.

  • Undefined/Complex Media: Contains unknown ingredients.

Based on Composition and Use

  1. General Purpose Media: Growth of most bacteria.

  2. Minimal Media: Provides minimal nutrients for specific organisms.

  3. Selective Media: Growth of selected microorganisms only.

  4. Differential Media: Distinguishes microorganisms based on biochemical characteristics.

  5. Transport Media: For specimens that can’t be cultured immediately.

  6. Enriched Media: Contains supplements for specific microorganisms.

Consistency of Culture Media

  • Liquid Medium (Broth): No solidifying agent.

  • Semi-Solid Medium: Contains small agar amounts for motility studies.

  • Solid Medium (Agar): Larger agar amounts used for isolating bacteria.

Microbiological Culture Techniques

Microbial Culture

  • Method of multiplying microorganisms in controlled conditions.

Techniques for Culture

  1. Streak Plate Culture: Isolates bacteria from mixed cultures.

  2. Pour Plate Culture: Serial dilutes samples in agar.

  3. Spread Plate Technique: Spreads diluted culture on agar surface.

Maintenance of Bacterial Culture

Techniques

  1. Periodic Transfer: Regular transfers to fresh medium.

  2. Mineral Oil: Extends culture life.

  3. Formaldehyde: Preserves agar cultures.

  4. Lyophilization: Freeze-drying for long-term preservation.

  5. Liquid Nitrogen: Storing at very low temperatures.

  6. Soredelli's Method: Specific method for preservation.

Measurement of Microbial Growth

Techniques

  • Cell Mass Measurement: Dry weight, cell volume, turbidimetric methods.

  • Cell Number Measurement: Counting chambers, electronic counting, plate counting.

Strain Improvement

Key Aspects

  • Enhancing microbial strains for better metabolic capabilities.

Methods of Strain Improvement

  • Regulating enzyme activity, enhancing permeability, genetic manipulation.

Screening Methods

  • Selection for specific characteristics and metabolic pathway reconstruction.

Techniques for Strain Improvement

  1. Mutation: Spontaneous or induced changes.

  2. Recombination: Creating hybrids from different strains.

  3. Recombinant DNA Technology: Isolating genes.

  4. Transduction: DNA transfer via bacteriophages.

  5. Transformation: Uptake of foreign DNA.

  6. Conjugation: Plasmid transfer between cells.

  7. Protoplast Fusion: Joining cells lacking walls.

  8. Metabolic Engineering: Designing pathways to boost production.