Staphyloccus & Streptococcus

Question 1

How would you differentiate between Streptococci and Staphlocci?

Answer 1

Both are Gram +
and under gram stain, Streptococci line up one after the other like a strip. Staphylococci line up in clusters however.

Staphylococci are catalase + while Streptococci are Catalase -

Question 2

How can you distinguish species of Streptococci from one another?

Answer 2

Streptococci can be distinguished based on their ability to hemolyze red blood cells.

Beta -hemolytiic strep can completly lyse RBCs and there will be a clear zone around them in petri dish

Alpha-hemolytic can partially lyse RBCs and there will be a greenish zone around them in the petri dish

Gamma-hemolytic can’t hemolyze RBC’s at all.

Question 3

What is the other way to distinguish Streptococci?

Answer 3

They can be distinguished based on their Lancefield antigen type

There are five Lancefield antigen types, A, B, C, D, and E

Three of teh five disease causing Streptococci have a Lancefield antigen: A, B. and D

Question 4

What are the characteristics of Group A Beta-Hemolytic Streptococci?

Answer 4

Possess Lancefield antogen A

Are beta hemolytic

Catalase -

These are known as Streptococcus pyogenes

Cause strep throat, scarlet fever, rheumatic fever

Question 5

What are the components of the streptococcal cell wall are antigenic?

Answer 5

C carbohydrate - Lancefield Group A

M protein - This is the major viruelence factor for Group A Beta Hemolytic Streptococci. It inhibits the activation of complement and protects organism from phagocytosis.

Streptolysin O - Destroys red blood cells

Pyrogenic exotoxin - Causes scarlet fever

Question 6

What is the cause of toic shock syndrome?

Answer 6

Streptococcus Beta Hemolytic Group A and Staphylococcus arreus

Question 7

Lancefield Group A Beta Hemolytic Streptococcus

Answer 7

Catalase -

Beta hemolytic

Aerophillic

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