Streptococci

Question 1

Give some examples of exotoxins (4)

Answer 1

Cytolytic
AB toxins
Superantigens
Enzymes

Question 2

What type of bacteria are streptococci?

Answer 2

Gram positive cocci

Question 3

How do streptococci group together?

Answer 3

Lines of balls

Question 4

How can streptococci be classified?

Answer 4

By haemolysis ability

Breaking down red blood cells

Question 5

What are the 3 classifications of streptococci according to haemolysis ability?

Answer 5

Alpha haemolysis- partial breakdown

Beta haemolysis - complete breakdown

Non-haemolytic gamma- no breakdown

Question 6

What are alpha haemolysis strep also called and give an example of a strept in this classification

Answer 6

‘Viridans’ streptococci (viridans meaning green because you will see a green colour on a culture)

Example: streptococcus pneumoniae

Question 7

Give an example of a beta haemolysis streptococci?

Answer 7

• Streptococcus pyogenes (pus forming potential)
• Streptococcus agalactiae
• Streptococcus dysgalactiae

More likely to show white on a culture as red blood cells are completely broken down

Question 8

Give an example of a non-haemolytic gamma streptococci

Answer 8

Enterococcus faecalis

Would show no change in colour

Question 9

Why is Streptococci agalactiae so important in neonates?

Answer 9

Because it causes meningitis and sepsis and is found naturally in the vagina

Question 10

What classification is given to streptococcus pyogenes?

Answer 10

Lancefield group A beta-haemolytic streptococcus

Question 11

What virulence factors does streptococcus pyogenes have? (8)

Answer 11

• hyaluronic acid capsule (inhibit phagocytosis)
• M protein (inhibits phagocytosis and helps with adhesion)
• Adhesins (adhesion)
• streptolysins O and S (lysis of neutrophils, erythrocytes and platelets)
• Dnases A, B, C and D (break down DNA)
• hyaluronidase (break down hyaluronic acid: connective tissue)
• streptokinase (break down clots and connective tissue)
• streptococcal pyrogens exotoxins (break down antibodies)

Question 12

How are streptococci grouped according to the Lancefield antigen?

Answer 12

A-F

Looks at ability of the cell wall to react with certain antibodies,
If it is a group A strep, that means it reacts with a group A antibody

*if you have an unknown beta haemolytic streptococcus then react it with antibodies and you can identify it according to which one it reacts with

Question 13

What is streptococcal toxic shock syndrome?

Answer 13

Deep tissue infection with strep pyogenes 
\+ 
Bacteraemia
\+
Vascular collapse (BP drops)
\+
Organ failure
= 

From health to death in hours

Question 14

What causes streptococcal toxic shock syndrome?

Answer 14

Entry of group A strep into deeper tissues and bloodstream

Question 15

How does group A strep cause vascular collapse and organ failure in streptococcal toxic shock syndrome?

Answer 15

It has virulence factors: streptococcal pyrogenic exotoxins (superantigens)

Which activate excessively the immune cells (ie T cells) and cause an inappropriately large immune response. This causes the drop in BP and organ failure.

M proteins also bind to fibrinogen and cause neutrophils to be activates= respiratory burst etc which causes endothelial damage