Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

ESA 2 - Infection > 6. Streptococci > Flashcards

6. Streptococci Flashcards

1
Q

Describe the gram stain appearance of streptococci.

A

gram positive (purple) cocci in chains

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Which type of agar plates can be used to classify streptococcal species?

A

blood agar - classify based of haemolytic ability

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What protein must a bacterium produce to perform haemolysis?

A

haemolysin

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What are the 3 types of streptococci based on haemolytic ability?

A
  1. alpha haemolysis (incomplete erythrocyte lysis)
    • causes wet green appearance of agar
    • displayed by S. pneumoniae and viridians Streptococci (group of oral bacteria)
  2. beta haemolysis (complete erythrocyte lysis)
    • causes white area around colonies
    • displayed by e.g. S. pyogenes
  3. gamma haemolysis (non-haemolytic)
    • e.g. Enterococcus faecalis
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Name 2 systems by which beta-haemolytic streptococcal species can be further classified.

A
  1. Lancefield serological classification: based on cell wall antigen (reaction with antibodies, groups A-F affect humans)
  2. Sherman group: pyogenic, viridans, enterococcal or lactic
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is the haemolytic, Lancefield and Sherman classification of S. pyogenes?

A
  • beta-haemolytic
  • Lancefield antigen A
  • pyogenic
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is the haemolytic, Lancefield and Sherman classification of S. pneumoniae?

A
  • alpha-haemolytic
  • no Lancefield antigen
  • viridans (but can be pyogenic)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

How is S. pyogenes transmitted?

A
  1. inhalation of droplets

2. skin-to-skin

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What is the main disease caused by inhalation of droplets containing S. pyogenes?

A

Streptococcal pharyngitis

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What are the clinical features of Streptococcal pharyngitis?

A
  1. abrupt onset sore throat
  2. fever
  3. malaise and headache
  4. lymphoid hyperplasia
  5. tonsillopharyngeal exudates
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Name 4 possible complications of Streptococcal pharyngitis.

A
  1. acute rheumatic fever
  2. acute post-streptococcal glomerulonephritis
  3. scarlet fever
  4. suppurative complications
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is acute rheumatic fever?

A

Inflammation of heart, joints and CNS caused by rheumatogenic M-type streptococcal strains.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Suggest possible explanations for the occurrence of rheumatic fever.

A

i) autoimmune (Ab cross-react with own antigen)
ii) serum sickness (reaction to Ab-Ag complex)
iii) binding of M protein to collagen (around heart/joints), streptolysin ASO or ASS induced injury

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What is acute post-streptococcal glomerulonephritis?

A

acute inflammation of renal glomerulus due to Ag-Ab complexes in glomerulus

caused by M-type specific strains (different to those in ARF)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is scarlet fever and what are the symptoms?

A

Local or haematogenous spread of streptococcal pyrogenic exotoxin strain.

Symptoms:

  • rash
  • high fever
  • sepsis
  • arthritis
  • jaundice
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Name possible suppurative complications of pharyngitis and explain their occurence.

A
  • peritonsillar cellulitis/abscess, retropharyngeal abscess, mastoiditis, sinusitis, otitis media, meningitis/brain abscess
  • due to spread of pus from tonsil into lateral pharyngeal space and then to system
17
Q

Name 4 possible S. pyogenes skin infections.

A
  1. impetigo
  2. erysipelas
  3. cellulitis
  4. necrotising fasciitis
18
Q

What is impetigo?

A

Childhood infection (2-5yrs) involving initial S. pyogenes skin colonisation followed by intradermal inoculation.

Most common cause of glomerular nephritis.

19
Q

What is erysipelas and what is it often preceded by?

A

S. pyogenes dermis infection with lymphatic involvement affecting face and lower limbs.

  • facial lesions often preceded by pharyngitis
  • lower limb infection usually secondary to skin invasion via trauma, skin disease or local fungal infection
20
Q

What is necrotising fasciitis?

A
  • infection of deeper subcutaneous tissues and fascia, usually secondary to skin break
  • rapid, extensive necrosis – severe pain, even before gross clinical changes, high fever, fulminant course, high mortality (20-70%)
21
Q

What is streptococcal toxic shock syndrome?

A
  • deep tissue infection with S. pyogenes + bacteraemia + vascular collapse + organ failure – from health to death in hrs
  • involves entry of group A Strep. into deeper tissues and bloodstream
22
Q

How do S. pyogenes virulence factors cause streptococcal toxic shock syndrome?

A
  • streptococcal pyrogenic exotoxins (superantigenic) overstimulate T cells through binding to MHC II APCs and V-β region of TCR (lower than normal), inducing monocyte cytokines (TNFα, IL-1 and IL-6) and lymphokines (TNFβ, IL-2, IFNγ)
  • M protein-fibrinogen complexes bind to neutrophils promoting degranulation, respiratory burst and endothelial damage
23
Q

How does S. pyogenes escape killing by the immune system?

A
  1. hyaluronic acid capsule - inhibits phagocytosis by macrophages and neutrophils. Poor immunogen due to similarity to human connective tissue hyaluronate.
  2. M protein (on surface) - inhibits activation of complement alternative pathway
  3. Streptolysins O and S - lysis of erythrocytes, neutrophils and platelets
24
Q

Which product produced by S. pyogenes and other beta-haemolytic streptococci can be used as a medication?

A

streptokinase - dissolution of clots through conversion of plasminogen to plasmin

ESA 2 - Infection (25 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions