Session 6 Lecture 1

Question 1

What shape is streptococci?

Answer 1

Gram positive cocci

Question 2

What are the different ways you can classify streptococci based on haemolysis?

Answer 2

• alpha haemolysis
• beta haemolysis
• non-haemolytic gamma

Question 3

What is the action of alpha haemolysis on a blood agar?

Answer 3

Partial breakdown

Question 4

What is the action of beta haemolysis streptococci on a blood agar?

Answer 4

Complete break down of the red blood cells

Question 5

What is the action of non-haemolytic gamma streptococci on a blood agar?

Answer 5

No red blood cells are destroyed

Question 6

Give an example of beta haemolytic streptococci?

Answer 6

Streptococci pyogenes

Question 7

Give an example of an alpha haemolytic streptococci?

Answer 7

Streptococcus pneumoniae

Question 8

Give an example of a non-haemolytic gamma streptococci?

Answer 8

Enterococcus faecalis

Question 9

What is another name for alpha haemolytic streptococci?

Answer 9

Viridans’ streptococci

Question 10

Define pyogenic

Answer 10

Pus producing

Question 11

Classify streptococcus pyogenes?

Answer 11

Lancefield group A beta haemolytic streptococcus

Question 12

How can you divide the streptococcus pyogenes virulence factors into groups?

Answer 12

Somatic virulence factors and exotoxic virulence factors

Question 13

What are somatic virulence factors?

Answer 13

Stuck to the cell (integral part of the organism)

Question 14

What are exotoxic virulence factors?

Answer 14

Released from the cell

Question 15

Name some streptococcus pyogenes virulence factors?

Answer 15

Hylauronic acid capsule, M protein, Adhesin, Streptolysins, DNAases

Question 16

How does hylauronic acid perform as a virulence factor?

Answer 16

Inhibits phagocytosis and poor immunogen because of its similarity to human connective tissue

Question 17

How does M protein act as a virulence factor?

Answer 17

Resistance to phagocytosis by inhibiting activation of alternative complement pathway on bacterial cell surface.

Question 18

How does adhesin work as a virulence factor?

Answer 18

Adhesion is the first step in colonisation/infection

Question 19

What causes streptococcal pharyngitis?

Answer 19

Streptococcus pyogenes

Question 20

Between which ages is streptococcal pharyngitis most common?

Answer 20

5-15 years

Question 21

How is streptococcal pharyngitis spread?

Answer 21

Droplet spread therefore association with overcrowding

Question 22

What are the clinical features of streptococcal pharyngitis?

Answer 22

Abrupt onset sore throat, malaise, fever, headache , lymphoid hyperplasia, tonsilopharangeal exudates

Question 23

What would a a throat swab of someone with strep pharyngitis show?

Answer 23

Group A strep

Question 24

What are the complications of streptococcal pharyngitis?

Answer 24

Scarlet fever, suppurative complications, acute rheumatic fever

Question 25

How does scarlet fever arise from streptococcal pharyngitis?

Answer 25

Due to infection with streptococcal pyrogens exotoxin strain of s.pyogenes

Question 26

What are some clinical features of scarlet fever?

Answer 26

High fever, sepsis, arthritis and jaundice

Question 27

How might suppurative complications arise from streptococcal pharyngitis?

Answer 27

Pus breaks off from tonsil and travels to the sternum

Question 28

Give examples of suppurative complications?

Answer 28

Peritonsillar cellulitis/abscess, retropharyngeal abscess, mastoiditis, sinusitis, otitis media and meningitis

Question 29

What is acute rheumatic fever?

Answer 29

Inflammation of heart, joints and CNS.

Question 30

Give examples of streptococcus pyogenes skin infections?

Answer 30

Impetigo and erysipelas

Question 31

Who is affected by impetigo?

Answer 31

Childhood infection 2-5 years

Question 32

How does impetigo present?

Answer 32

Initial skin colonisation, followed by intradermal innoculation

Question 33

Impetigo is the most common cause of...

Answer 33

Glomeruonephritis

Question 34

What is erysipelas?

Answer 34

Dermis infection with lymphatic involvement

Question 35

What areas of the body does erysipelas affect?

Answer 35

Face and lower limbs

Question 36

What other skin infections can be caused by streptococcus pyogenes?

Answer 36

Cellulitis and necrotising fasciitis

Question 37

What is cellulitis?

Answer 37

Skin and subcutaneous tissue infection

Question 38

What is necrotising fasciitis?

Answer 38

Infection of deeper subcutaneous tissues and fascia | Rapid, extensive necrosis

Question 39

What causes streptococcal toxic shock syndrome?

Answer 39

Deep tissue infection with strep pyogenes and bacteraemia and vascular collapse and organ failure

Question 40

What is the prognosis of someone with streptococcal toxic shock syndrome?

Answer 40

From health to death in hours