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Infection 2023 > Streptococci > Flashcards

Streptococci Flashcards

1
Q

Streptococci gram stain

A

Gram +ve cocci

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2
Q

How are streptococci classified?

A

By haemolysis

Serologically (Lancefield - for beta haemolytic)
Pyogenic (Sherman pus or not)
16S ribosomal RNA sequencing

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3
Q

Types of streptococci haemolysis

A

alpha haemolysis: partial haemolysis, viridans streptococci (green stain)

beta haemolysis: complete haemolysis, gain iron, grow abundantly

non haemolytic (gamma) haemolysis

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4
Q

alpha, beta haemolytic and non haemolytic examples

A

alpha: streptococcus pneumoniae
beta: streptococcus pyogenes

Non haemolytic: Enterococcus faecalis

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5
Q

Sherman classification

A

Pyogenic or not
All beta haemolysis strep are pyogenic
All alpha haemolysis are viridans

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6
Q

Streptococcus pyogenes classification

A

Lancefield Group A

Beta haemolytic streptococcus

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7
Q

Streptococcus causing abscesses

A

Streptococcus anginosus spp

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8
Q

Mouth commensal streptococcus

A

Streptococcus mutans
Streptococcus salivarius

(can cause endocarditis)

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9
Q

Virulence factors for streptococcus pyogenes

A 
Hyaluronic capsule 
M protein
Adhesins (lipoteichoic acid, M protein, fibronectin binding proteins)
Streptolysins O and S
DNAses ABCD
Hyaluronidase 
Streptokinase 
Streptococcal pyrogenic exotoxins
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10
Q

Hyaluronic acid capsule function

A

Inhibits phagocytosis by neutrophils and macrophages

similar to human connective tissue hyaluronate

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11
Q

M protein function

A

Resistance to phagocytosis by inhibiting activation of complement pathway

Different serotypes from emm gene

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12
Q

Adhesins function

A

First step in colonisation/infection

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13
Q

Streptolysins O and S function

A

Lysis of erythrocytes, neutrophils and platelets

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14
Q

DNAases ABCD

A

Degrade DNA

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15
Q

Hyaluronidase function

A

Degrade hyaluronic acid in connective tissue

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16
Q

Streptokinase function

A

Dissolution of blood clots - converts plasminogen to plasmin (inactive to active)

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17
Q

Streptococcal pyrogenic exotoxins function

A

Cleaves IgG bound to group A strep

Superantigenic Spe family (can cause clonal T cell proliferation - toxic shock)

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18
Q

M proteins appearance microscope

A

Fuzzy peach appearance of microbe

‘fur’ = M proteins

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19
Q

Streptococcal pharyngitis cause

A

Streptococcus pyogenes

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20
Q

How does streptococcal pharyngitis spread?

A

Droplet spread

Associated with overcrowding (poor living conditions and schools)

21
Q

When is streptococcal pharyngitis likely to occur?

A

5-15 years old

22
Q

What do untreated streptococcal pharyngitis patients develop?

A

M protein specific antibody

23
Q

Clinical features streptococcal pharyngitis

A

Abrupt onset sore throat
Malaise, fever, headache
Lymphoid hyperplasia

TONSILLOPHARYNGEAL EXUDATE
Throat swab = group A strep

24
Q

Complications of streptococcal pharyngitis and cause (main)

A

Scarlet fever - if infected with streptococcal pyrogenic exotoxin strain

25
Q

Spread of scarlett fever through body

A

Local or haematogenous

26
Q

Complications/signs associated with scarlett fever

A

High fever
Sepsis
Arthritis (joint swelling)
Jaundice

27
Q

Complications associated with pus and streptococcal pharyngitis (suppurative)

A

Peritonsillar cellulitis/abscess
Retropharyngeal abscess

Mastoiditis, Sinusitis, Otitis media

Meningitis, Brain abscess

28
Q

How does streptococcal pharyngitis spread from origin?

A

Through lateral pharyngeal space - could go to mediastinum or back up to head

29
Q

Acute complications of streptococcal pharyngitis

A

Acute rheumatic fever

Acute post-streptococcal glomerulonephritis

30
Q

What is acute rheumatic fever?

A

Inflammation of heart, joints and CNS (could cause endocarditis, pericarditis or epicarditis)

From Rheumatogenic M types following pharyngitis

31
Q

Mechanisms of acute rheumatic fever?

A

Autoimmune response to M proteins
Serum sickness
Binding of M protein to collagen
ASO (antistreptolysin O titier) or ASS induced tissue injury

32
Q

What is acute post-streptoccocal glomerulonephritis

A

Acute inflammation of renal glomerulus
M type specific

Antigen-antibody complex in glomerulus - blood sticks here

33
Q

When does RF occur after streptococcal pharyngitis

A

Delayed onset.

Patient seems to be getting better and then gets worse

34
Q

Streptococcus pyogenes skin infection

A

Impetigo

Erysipelas

35
Q

Impetigo

A 
Childhood infection (2-5 years old)
Skin colonisation and then intradermal inoculation

No acute rheumatic fever but COMMON cause of glomerulonephritis

36
Q

Erysipelas

A

Dermis infection with lymphatic involvement
Face/lower limbs

Facial lesions = usually following pharyngitis
Leg lesions = usually from skin invasion via trauma, skin disease or local fungal infection

37
Q

Impetigo vs erysipelas appearance

A

Impetigo: Crusty around mouth in particular

Erysipelas: Redness with pronounced margins

38
Q

Streptococcus pyogenes skin infections

A

Cellulitis

Necrotising fasciitis

39
Q

Cellulitis + risk factors

A

Skin and subcutaneous tissue infection

RISK FACTORS:
Impaired lymphatic drainage
Injecting drug use

40
Q

Necrotising fasciitis

A 
Infection deeper of subcutaneous tissue causing rapid and extensive necrosis 
Severe pain (even before gross clinical changes)
41
Q

Risk factor necrotising fasciitis

A

Secondary to skin break

42
Q

Necrotising fasciitis problems

A

High fever
Severe/sudden onset
High mortality rate

43
Q

Testing for necrotising fasciitis

A

Sweep test
See if can sweep finger under subcutaneous tissue
If you can, shows necrosis is present and +ve for NF

44
Q

Streptococcal toxic shock syndrome cause (steps)

A 
Deep tissue infection with streptococcus pyogenes
\+
Bacteraemia
\+
Vascular collapse 
\+
Organ failure
45
Q

What occurs in streptococcal toxic shock syndrome?

A

Group A strep enters deeper tissues and blood

Streptococcal pyrogenic exotoxins stimulate T cells by binding to MHC class 2 on APC cells and V beta region of T cells

Induces monocyte cytokines and lymphokines

M protein fibrinogen complex formation

46
Q

Cytokines and lymphokines released during strep A infection

A

Cytokines - TNF-alpha, IL1B, IL6

Lymphokines - TNF beta, IL2, IFN-gamma

47
Q

What does M protein fibrinogen complex cause

A

Bind to integrins on neutrophils
Activates them and they adhere to endothelium and degranulate

Release hydrolytic enzymes and respiratory burst

48
Q

What does respiratory burst to endothelium?

A

hypercoagulable state –> disseminated intravascular coagulation

tissue damage –> vascular leakage –> hypotension
Lack of organ perfusion = organ failure

Infection 2023 (29 decks)

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