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Identification of Staphylococci and Streptococci: Tests and Differentiation Methods

This exercise focuses on various tests and methods used to differentiate between Staphylococci and Streptococci bacteria. Topics covered include the catalase test, coagulase, Mannitol Salt Agar (MSA), Novobiocin sensitivity, hemolysis, Bacitracin sensitivity, and Bile Esculin test.

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Identification of Staphylococci and Streptococci: Tests and Differentiation Methods

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  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

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