Session 6 - Streptococci

Question 1

what gram stain do streptococci give

Answer 1

gram positive and found in strings

Question 2

what is haemolysis

Answer 2

destruction of RBCs

Question 3

what 3 haemolysis classifications are there of streptococci

Answer 3

• alpha/viridans
• beta
• non haemolytic/gamma

Question 4

what are alpha/ viridans haemolysis streptococci

Answer 4

streptococci which cause a partial break down of RBC to give a green, wet appearance of the blood

Question 5

give an example of an alpha haemolysis streptococcus

Answer 5

streptococcus pneumoniae

Question 6

what are beta haemolysis streptococci

Answer 6

streptococci which give a complete breakdown of RBCs giving a yellow appearance

Question 7

give an example of a beta haemolysis streptococcus

Answer 7

streptococcus pyogenes

Question 8

what are non haemolytic streptococci

Answer 8

streptococci which don’t break down RBCs

Question 9

what 2 classifications are there for streptococci

Answer 9

• Lancefield antigen (due to different antigens)

- Sherman group

Question 10

what type of streptococcus has the Lancefield antigen A

Answer 10

S pyogenes

Question 11

what type of streptococcus has the Lancefield antigen B

Answer 11

S agalactiae

Question 12

name 6 virulence factors of Steptococcus pyogenes

Answer 12

• hyaluronic acid capsule
• M proteins
• adhesins
• Dnases
• hyaluronidase
• streptokinase

Question 13

what does the hyaluronic capsule do

Answer 13

inhibits phagocytosis

as hyaluronic acid is already found in CT its not seen as foreign

Question 14

what do M proteins do

Answer 14

resist phagocytosis by inhibiting the complement pathway

Question 15

what do adhesins do

Answer 15

prevent adhesion

Question 16

what do Dnases do

Answer 16

degrade DNa

Question 17

what do hyaluronidase do

Answer 17

degrades hyaluronic acid in CT

Question 18

what causes streptococcus pharyngitis

Answer 18

streptococcus pyogenes

Question 19

what are the clinical features of streptococcus pharyngitis

Answer 19

• fever
• headache
• exudate of pus on tonsils
• enlarged tonsils

Question 20

how is streptococcus pharyngitis spread

Answer 20

by droplets

Question 21

what are complications of streptococcus pharyngitis

Answer 21

• scarlet fever
• peritonsillar abscess
• meningitis
• rheumatic fever
• post-streptococcal glomerulonephritis

Question 22

what is scarlet fever and why is it a complication of streptococcus pharyngitis

Answer 22

• infection characterised by a pink rash and high fever

- caused by exotoxin of streptococcus pyogenes

Question 23

what is rheumatic fever and why is it a complication of streptococcus pharyngitis

Answer 23

• inflammation of the heart, joints and CNS

- the bacteria cause an auto immune response as the specific M proteins from a specific S pyogene binds to collagen

Question 24

what is post-streptococcal glomerulonephritis

Answer 24

acute inflammation of the renal glomerulus caused by S pyogenes with the specific M protein

Question 25

what S pyogenes skin infections are there

Answer 25

impetigo (just affects dermis - raised edges)
erysipelas (affects dermis and lymphatics - raised edges) 
cellulitis (skin and subcutaneous tissue affect but no raised) 
necrotising fasciitis (infection of deep skin and muscles very rapidly)

Question 26

what is streptococcal toxic shock syndrome

Answer 26

where there is entry of group A strep into deeper tissues and the bloodstream causing vascular collapse (due to the superantigen exotoxins causing proliferation of t cells giving a huge immune response) resulting in organ failure