Gram Positive Media
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What are the two types of agar we use for gram positive media?
- blood agar
- mannitol salt agar
What is a blood agar? What blood is commonly used and why?
- enriched media
- supports growth of most bacterial pathogens
- sheep blood commonly used due to the hemolytic action by some bacteria on the RBCs
What is hemolysin?
- a substance (enzyme) produced by some bacterial cells
- digests RBCs
What are the 4 types of hemolysis in a blood agar?
What is alpha hemolysis? What does it look like?
- partial hemolysis
- narrow band of greenish or slimy discoloration around the bacterial colonies
What is beta hemolysis? What does it look like?
- complete hemolysis
- creates a clear zone around the bacterial colony
What is gamma hemolysis? What does it look like?
- produces no chance in the appearance of the media
- no hemolysis around colonies
What is delta hemolysis? What does it look like?
- double-zone hemolysis
- zone of hemolysis surrounded by a narrow zone of hemolysis around a bacterial colony
What is mannitol salt agar used for?
- selective media for Staphylococci
- high salt concentrations inhibits most other bacteria
What gives the mannitol salt agar the red appearance?
In the presence of acid, the phenol red turns _____. This indicates which type of bacteria?
- Staphylococcus aureus
What happens to the mannitol salt agar if there is Staphylococcus epidermidis?
does not ferment mannitol and media will stay red
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