9. Streptococci

Question 1

What class of bacteria is streptococci

Answer 1

Gram positive, chains

Question 2

What is haemolysis?

Answer 2

Using the ability of bacteria to breakdown red blood cells as a way of classifying the different micro organisms

Question 3

What colour does alpha haemolysis create? Give an example of a bacteria that carries out alpha haemolysis

Answer 3

Dark green

Viridans streptococci eg spretococcus pneumoniae

Question 4

What is beta haemolysis? Give an example of a bacteria that displays beta haemolysis

Answer 4

Complete haemolysis - produces a lightened (yellow) transparent area
Streptococcus pyogenes

Question 5

What is gamma haemolysis? Give an example of a bacteria that displays game haemolysis

Answer 5

No haemolysis occurs, so still looks the same.

Enterococcus faecalis

Question 6

What are the two different classification schemes for streptococci bacteria?

Answer 6

Lancefield, based on cell wall antigens, is letters

Sherman, eg pyogenic, viridans etc

Question 7

What main class of bacteria causes abscesses?

Answer 7

Pyogenic

Question 8

Give 2 virulence factors of streptococcus pyogenes

Answer 8

Hyaluronic acid capsule - inhabiting phagocytosis by neutrophils and macrophages, and making it a poor immunogenicity due to similarity to human connective tissue hyaluronate
M protein - resistance to phagocytosis by inhibiting activation of alternative complement pathway on bacterial cell surface
Adhesions - aiding colonisation/infection

Question 9

What is the bacterial cause of streptococcal pharyngitis?

Answer 9

Streptococcus pyogenes

Question 10

How is streptococcal pharyngitis spread?

Answer 10

Droplet spread, associated with overcrowding

Question 11

What do untreated patients with streptococcal pharyngitis develop?

Answer 11

M protein specific antibody (aid in opsonisation and destruction of the microorganism my macrophages and neutrophils)

Question 12

Name 4 complications of streptococcal pharyngitis

Answer 12

Scarlet fever
Suppurative complications eg meningitis (brain abscess)
Acute rheumatic fever
Acute post-streptococcal glomerulonephritis

Question 13

What is scarlet fever? What causes it?

Answer 13

Infection with streptococcal pyogenic exotoxin strain of S.pyogenes.
Local or haematogenous spread.
High fever, sepsis, arthritis, jaundice

Question 14

What is acute rheumatic fever? Give 2 possible causes of it

Answer 14

Inflammation of the heart, joints, central nervous system. Occurs ONLY after pharyngitis, not from other streptococcal infections
There are rheumatogenic M types
Auto-immune, binding of M protein to collagen

Question 15

What is acute post-streptococcal glomerulonephritis? What causes it?

Answer 15

Acute inflammation of the renal glomerulus
M type specific
Antigen-antibody complexes deposited in the glomerulus

Question 16

What is impetigo? What secondary condition is it the most common cause of?

Answer 16

Common in children 2-5yrs
Skin colonisation and then intradermal inoculation
Most common cause of glomeruonephritis

Question 17

What is erysipelas?

Answer 17

Dermis infection with lymphatic involvement, affecting the face and lower limbs
Facial lesions preceded by pharyngitis
Lower limb infection usually secondary to trauma, skin disease or local fungal infection leading to streptococcus pyogenes invasion of the skin

Question 18

What is cellulitis? What are two important risk factors for developing cellulitis?

Answer 18

Skin and subcutaneous tissue infection

Impaired lymphatic drainage and illicit injecting drug use

Question 19

What is necrotising fasciitis? What is it associated with?

Answer 19

Infection of deeper subcutaneous tissues and fascia, with rapid, extensive necrosis, usually secondary to skin break
Severe pain even before gross clinical changes
High fever, very rapid onset, high mortality

Question 20

What is streptococcal toxic shock syndrome?

Answer 20

Deep tissue infection with strep pyogenes, bacteraemia, vascular collapse, organ failure (thought to be caused by formation of M-protein fibrinogen complex)

Question 21

Give 3 infections that streptococcus pneumoniae can cause

Answer 21

Community-acquired pneumonia
Adult bacterial meningitis
Sinusitis

Question 22

Is streptococcus pneumoniae gram positive or negative?

Answer 22

Gram-positive

Question 23

What two properties does the capsule of streptococcus pneumoniae possess?

Answer 23

Antiphagocytic

Antigenic

Question 24

Does pharyngitis caused by streptococcus pyogenes cause white exudate to form on the throat and tonsils?

Answer 24

Yes, EBV does not

Question 25

What is another cause of pharyngitis?

Answer 25

EBV causing infectious mononucleosis (glandular fever)

Question 26

What cell is first infected by EBV, and which is infected after this? What happens to the second type of cell?

Answer 26

Oropharyngeal epithelium

B lymphocytes - latency and immortalisation

Question 27

What type of viral infection does EBV belong to?

Answer 27

Latent infection

Question 28

What group of viruses does EBV belong to?

Answer 28

Human herpes virus