WEEK 8

Identification of Staphylococci and Streptococci

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

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

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)

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

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

Exercise 6: Bacitracin Sensitivity

• Used to determine the species of Streptococci

• Bacitracin is an antibiotic

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