Streptococcus

Question 1

streptococi characteristics

Answer 1

(especially pyogenes)

• Gram positive

Question 2

how do you classify streptocci

Answer 2

haemolysis

Question 3

explain haemolysis

Answer 3

Use agar with blood (horse or sheep)- with RBC.

• Iron is a requirement for many bacteria, therefore haemolysis to get iron

Question 4

partial haemolysis

Answer 4

alpha haemolysis

e.g. viridans (green) streptococcus

(live in the mouth)

Question 5

complete haemolysis

Answer 5

beta haemolysis

• streptocccus pyogenes

Question 6

no haemolysis

Answer 6

gamma non-hamolysis

e.g. enterococcus faecalis

Question 7

streptococcus classification schemes

Answer 7

Question 8

streptococcus pyogenes virulence factors

Answer 8

• hyaluornic acid capsule
• M protein
• Adhesins
• Streptolysins O and S
• DNAases A, B, C and D
• Hyaluronidase
• streptokinase
• streptooccal pyrogenic exotoxins

Question 9

Hyaluronic acid capsule

Answer 9

• Inhibits phagocytosis by neutrophils and macrophages
• Poor immunogen because of similarity to human connective tissue hyaluronate

Question 10

M protein

Answer 10

• • Resistance to phagocytosis by inhibiting activation of alternative complement pathway on bacterial cell surface
    
    • >150 antigenically different serotypes as a consequence of nucleotide variants of the M gene

Question 11

Adhesins (Lipoteichoic acid, M protein, fibronectin binding proteins)

Answer 11

Adherence is first step in colonisation/ infection

Question 12

Streptolysins O and S

Answer 12

Lysis of erythrocytes, neutrophils, platelets

Question 13

DNAases A, B, C and D

Answer 13

Degradation of DNA

Question 15

Hyaluronidase

Answer 15

Degradation of hyaluronic acid in connective tissue

Question 16

Streptokinase

Answer 16

Dissolution of clots through conversion of plasminogen to plasmin

Question 17

Streptococcal pyrogenic exotoxins

Answer 17

Cleaves Ig G bound to group A steep

Question 18

Streptococcus pyogenes M protein

Answer 18

If you stain bacteria correctly you can see fuzzy layerà M proteins

Question 19

Streptococcal pharyngitis (tonsillitis)

Answer 19

• Causative organism: streptococcus pyogenes
• Most common at 5-15 years
• Droplet spread
• Association with overcrowding
• Untreated patients develop M protein specific antibodies

Question 20

clinical features of streptococcal pharyngitis

Answer 20

• Abrupt onset of sore threat
• Malaise, fever, headache
• Lymphoid hyperplasia
• Tonsillopharyngeal exudates
• Throat swab –> Group A strep

Question 21

Complications of streptococcal pharyngitis

Answer 21

scarlet fever

suppurative complications

acute rheumatic fever

acute post-streptococcal glomerulonephritis

Question 22

Scarlet fever

Answer 22

• Due to infection with streptococcal pyrogenic exotoxin strain of S. Pyogenes
• Local or haematogenous spread
• High fever, sepsis, arthritis, jaundice
• 1800s epidemic with 20% mortality

Question 23

Suppurative complications

Answer 23

• Peritonsillar cellulitis/abscess (contiguous)
• Retropharyngeal abscess
• Mastoiditis, sinusitis, otitis media
• Meningitis, brain abscess (haematogenous spread)

Question 25

**Acute rheumatic fever**

Answer 25

* Inflammation of the heart, joints, CNS * Follow on from pharyngitis * No bacteria anymore (no point using antibiotics) * Rheumatogenic M types * Mechanisms (possible) * Auto-immune * Serum sickness * Binding of M protein to collagen * ASO, ASS induced tissue injury

Question 26

**Acute post-streptococcal glomerulonephritis**

Answer 26

* Acute inflammation of renal glomerulus * M type specific but not same as ARF M types * Antigen-antibody complexes in glomerulus

Question 27

**Streptococcus pyogenes skin infections**

Answer 27

impetigo erysipelas cellulitis necrotising fasciitis

Question 28

impetigo

Answer 28

* Childhood infection (2-5 years) * Initial skin colonisation followed by intradermal inoculation * No ARF but impetigo is most common cause of glomerulonephritis * Flucloxacillin

Question 30

**Erysipelas**

Answer 30

* Dermis infection with lymphatic involvement * Face, lower limbs * Facial lesions frequently preceded by pharyngitis * Lower limb infection usually secondary to invasion of skin via trauma, skin disease or local fungal infection

Question 31

**Cellulitis**

Answer 31

* Skin and subcutaneous tissue infection * Impaired lymphatic drainage and illicit injecting drug use important risk factor

Question 32

**Necrotising fasciitis (may require surgery)**

Answer 32

* Infection of deeper subcutaneous tissue and fascia * Rapid, extensive necrosis * Usually secondary to skin break * Severe pain, even before gross clinical changes * High fever, fulminant course, high mortality (20-70%)

Question 33

normal skin vs necrotising fascitis

Answer 33

Question 34

**Streptococcal toxic shock syndrome** *

Answer 34

* Deep tissue infection with strep pyogenes * And * Bacteraemia * And * Vascular collapse * And * Organ failure

Question 35

Deep tissue infection with strep pyogenes- from health to death in hours

Answer 35

1. Entry of group A strep into deeper tissue sand bloodstream 2. Streptococcal pyrogenic exotoxins stimulate T cells through binding to MHC class II APC and V-B region of T cell receptor inducing: 1. Monocyte cytokines (TNF-alpha, IL-1B, IL-6) and lymphokines (TNF-B, IL-2, IFN-Y) 2. M-protein fibrinogen complex formation