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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
Spread of scarlett fever through body
Local or haematogenous
26
Complications/signs associated with scarlett fever
High fever Sepsis Arthritis (joint swelling) Jaundice
27
Complications associated with pus and streptococcal pharyngitis (suppurative)
Peritonsillar cellulitis/abscess Retropharyngeal abscess Mastoiditis, Sinusitis, Otitis media Meningitis, Brain abscess
28
How does streptococcal pharyngitis spread from origin?
Through lateral pharyngeal space - could go to mediastinum or back up to head
29
Acute complications of streptococcal pharyngitis
Acute rheumatic fever | Acute post-streptococcal glomerulonephritis
30
What is acute rheumatic fever?
Inflammation of heart, joints and CNS (could cause endocarditis, pericarditis or epicarditis) From Rheumatogenic M types following pharyngitis
31
Mechanisms of acute rheumatic fever?
Autoimmune response to M proteins Serum sickness Binding of M protein to collagen ASO (antistreptolysin O titier) or ASS induced tissue injury
32
What is acute post-streptoccocal glomerulonephritis
Acute inflammation of renal glomerulus M type specific Antigen-antibody complex in glomerulus - blood sticks here
33
When does RF occur after streptococcal pharyngitis
Delayed onset. | Patient seems to be getting better and then gets worse
34
Streptococcus pyogenes skin infection
Impetigo | Erysipelas
35
Impetigo
``` Childhood infection (2-5 years old) Skin colonisation and then intradermal inoculation ``` No acute rheumatic fever but COMMON cause of glomerulonephritis
36
Erysipelas
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
Impetigo vs erysipelas appearance
Impetigo: Crusty around mouth in particular Erysipelas: Redness with pronounced margins
38
Streptococcus pyogenes skin infections
Cellulitis | Necrotising fasciitis
39
Cellulitis + risk factors
Skin and subcutaneous tissue infection RISK FACTORS: Impaired lymphatic drainage Injecting drug use
40
Necrotising fasciitis
``` Infection deeper of subcutaneous tissue causing rapid and extensive necrosis Severe pain (even before gross clinical changes) ```
41
Risk factor necrotising fasciitis
Secondary to skin break
42
Necrotising fasciitis problems
High fever Severe/sudden onset High mortality rate
43
Testing for necrotising fasciitis
Sweep test See if can sweep finger under subcutaneous tissue If you can, shows necrosis is present and +ve for NF
44
Streptococcal toxic shock syndrome cause (steps)
``` Deep tissue infection with streptococcus pyogenes + Bacteraemia + Vascular collapse + Organ failure ```
45
What occurs in streptococcal toxic shock syndrome?
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
Cytokines and lymphokines released during strep A infection
Cytokines - TNF-alpha, IL1B, IL6 Lymphokines - TNF beta, IL2, IFN-gamma
47
What does M protein fibrinogen complex cause
Bind to integrins on neutrophils Activates them and they adhere to endothelium and degranulate Release hydrolytic enzymes and respiratory burst
48
What does respiratory burst to endothelium?
hypercoagulable state --> disseminated intravascular coagulation tissue damage --> vascular leakage --> hypotension Lack of organ perfusion = organ failure

Infection 2023 (29 decks)

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