WEEK 8

1. WEEK 8 Identification of Staphylococci and Streptococci

2. Exercise 1: Catalase Test • Used to differentiate between Staphylococci and Streptococci • Test for Catalase – an enzyme that breaks down hydrogen peroxide • If bubble form, it is a positive for catalase • Staphylococci is catalase positive whereas streptococci is negative

3. Exercise 2: Coagulase • Allows us to differentiate between different forms of Staphylococci • Coagulase is an enzyme produced by Staphylococci Aureus and not the other forms of Staphylococci • Forms plasma clots around itself for protection

4. Exercise 3: Mannitol Salt Agar (MSA) • Allows us to differentiate between different forms of Staphylococci • Selective for Staphylococci • Differential for pathogenic form Staph. Aureus • Looking for fermentation of mannitol (yellow)

5. Exercise 4: Novobiocin Sensitivity Test • Used to differentiate between different forms of Staphylococci bacteria • Novobiocin is an antibiotic • S. saprophyticus is resistant to novobiocin, while S. aureus and S. epidermidis are susceptible

6. Exercise 5: Hemolysis • Used to determine the species of Streptococci • Enzyme called Hemolysin • Beta-hemolytic streptococci completely hydrolyze red blood cells • Alpha-hemolytic streptococci partially hydrolyze red blood cells • gamma-hemolytic (or Non-hemolytic) are not hemolytic at all and do not affect the red blood cells

7. Exercise 6: Bacitracin Sensitivity • Used to determine the species of Streptococci • Bacitracin is an antibiotic

8. Exercise 7: Bile Esculin Test • Used to determine the species of Streptococci • Plate contains bile, which inhibits the growth of organisms except Group D streptococci and enterococci • Group D streptococci and enterococci can hydrolyze esculin into glucose and esculetin. • The glucose is used for energy metabolism and the esculetin reacts with iron salts in the media to form a black precipitate which verifies presence of a Group D strep or enterococci