Overview
This lecture covers different types of growth media used in microbiology labs, including their definitions, purposes, and examples.
Types of Growth Media
- Complex media contains a mixture of ingredients where the exact composition is unknown (e.g., nutrient broth, tryptic soy broth).
- Chemically defined media has a precisely known composition, used when exact nutrient content is required.
Enriched and Enrichment Media
- Enriched media provide specific nutrients needed by fastidious (nutrient-demanding) organisms that cannot grow on standard media.
- Chocolate agar is an example of enriched media, containing treated blood to support organisms like Haemophilus influenzae.
Selective Media
- Selective media inhibit unwanted microorganisms and allow the growth of desired ones.
- Example: Agar plates containing ampicillin select for genetically modified E. coli resistant to the antibiotic.
- McConkey's Agar contains bile salts and crystal violet to inhibit gram-positive bacteria and allow gram-negative gut bacteria to grow.
Differential Media
- Differential media allow visual differentiation of microbial species based on biochemical characteristics.
- McConkey's Agar includes a pH indicator to distinguish lactose fermenters (e.g., E. coli turns the plate pink) from non-fermenters (e.g., Serratia marcescens remains uncolored).
- Blood agar shows hemolysis (clear zones) caused by bacteria that lyse red blood cells.
Key Terms & Definitions
- Complex Media — Growth medium with unknown exact composition.
- Chemically Defined Media — Growth medium with precisely known chemical composition.
- Enriched Media — Medium supplemented with specific nutrients to support fastidious organisms.
- Fastidious — Organisms that require specific nutrients to grow.
- Selective Media — Media that suppresses unwanted microbes and encourages desired ones.
- Differential Media — Media allowing visual identification of microbial traits.
- Chocolate Agar — Enriched medium with treated blood supporting specific bacteria.
- McConkey's Agar — Selective and differential medium for gram-negative bacteria.
- Blood Agar — Enriched, selective, and differential medium used for hemolysis detection.
Action Items / Next Steps
- Review key definitions of each type of growth media.
- Be able to give examples of selective, differential, enriched, and complex media.
- Prepare for questions on how different media types are used in lab settings.