Lab 7: Selective and Differential Media

Enriched Media

• Enriched media is designed to support the growth of a wide variety of organisms by providing all necessary nutrients.
• Examples include Tryptic Soy Agar (TSA) and Blood Agar.

Blood Agar Plates (BAP)

• Blood Agar is both a differential and enriched medium used for growing bacteria.

Hemolytic Reactions

• Observing hemolytic reactions on sheep blood agar aids in the preliminary identification of bacteria, particularly streptococci.
• Types of hemolysis include alpha (α), beta (β), and gamma (γ).

Purpose of Blood Agar

• Blood agar is utilized to determine the types of hemolysis exhibited by bacterial colonies.

Interpretation of Hemolysis

• Beta-hemolysis results in complete lysis of red blood cells, characterized by a transparent zone around colonies.
• Alpha-hemolysis shows partial clearing and a green or brownish ring.
• Gamma-hemolysis exhibits no hemolytic activity with no discoloration.

Alpha-Hemolysis

• Streptococcus pneumoniae and several oral streptococci display alpha-hemolysis, presenting with a greenish discoloration around colonies.

Beta-Hemolysis Organisms

• Organisms classified as beta-hemolytic include Streptococcus pyogenes, Streptococcus agalactiae, and Staphylococcus aureus.
• Beta-hemolytic bacteria cause complete lysis of red blood cells, leaving a clear zone on the agar.

Identifying Beta-Hemolysis

• Streptococcus pyogenes is a notable example of a beta-hemolytic organism.

Gamma-Hemolysis

• Gamma hemolysis refers to the lack of hemolytic activity, where no discoloration is produced on the agar (e.g., E. coli).

Growth of Neisseria gonorrhoeae

• Neisseria gonorrhoeae does not grow on sheep blood agar due to its fastidious nature.

This quiz focuses on the concepts of selective and differential media, particularly Blood Agar. Flashcards cover definitions, examples, and characteristics of enriched media used in microbiological studies. Test your knowledge on the types and uses of various media in laboratory settings.