Lecture 2 - Streptococcal Infection Flashcards
Where are strep found
Everywhere
Gut, GI tract, mouth, URT
What is the classification of streptococcal
Streptococci
What is the pathogenic form of streptococcus
Strep pyogenes - Group A streptococcus
Who first described pyogenes infected patients with a ‘flesh eating disease’
Hippocrates
Who in 1874 designated the name strepto coccus
Theodore Billroth
Who in 1884 was the first person to recover and grow strep pyogenes from patients with puerperal sepsis (childbed fever)
Louis Pasteur
In 1884 which pioneer designated name streptococcus pyogenes
Anton rosenbach
Why is it called pyogenes
Pyo meaning inflammatory
Cause inflammation
Is strep pyogenes gram positive or gram negative
Gram positive
What is the size of strep pyogenes
0.5-1um
How do strep pyogenes gain energy E.g. Via oxygen or co2
FACULTATIVE ANAEROBES
What does capnophilic mean
Bacteria that live in high CO2
What temperate range does strep pyogenes fit into
18-40
Optimum 30
Is strep pyogenes positive or negative for catalase production
Catalase NEGATIVE
Where does S.salivarius live
MOUTH
What does S.agalactiae cause
Neonatal meningitis
Name 3 diseases caused by strep pyogenes
Tonsillitis, necrotising fasciitis (gangrene) and scarlet fever
What is a key factor of strep classification
Their haemolytic properties e,g, alpha, beta or gamma
And SURFACE ANTIGENS E.G. CHO antigens, classifies beta haemolytic strep into specific groups of carbohydrate surface antigen A,B,C,G,F
What enzymes are used in beta haemoyosis to break down our RBC
Streptolysin S and O
Who based classification on surface antigens
Rebecca lancefield
What strep species partake in partial haemolysis (alpha)
S. Pneumoniae and viridians strep
What does hydrogen peroxide produced by the alpha haemolytic species do the haemoglobin
Oxidises to green methaemoglobin
Which two species of strep partake in beta haemolysis
strep pyogenes and s,agalactiae
What do type II toxin do
Attack cholesterol in membrane
Which streptolyosin is oxygen labile and which is oxygen stable
Labile - streptolysin O
Stable S - use oxygen
Which species partake in gamma haemolysis
Enterococcus
Rebecca lancefield identified two major surface antigens that could be used in classification of beta haemolytic strep. What are they?
M proteins
Group Antigen
Surface antigen is a carbohydrate antigen incorporated into cell wall by strep. How do we extract it in the laboratory
Mix colony with nitrous acid and this brings the surface antigen away.
Also do a variety of agglutination tests using latex beads with antibodies against all group antigens e.g. Group A or B etc
How many M proteins are there believed to be
Up to 18
What is the group A antigen
NAG - rhamnose. Group A antigen surround cell wall particularly rhamnose
What doesnt the antigen classification tell you and how do you resolve this
Species and genus
Use API - sugars and enzymes. If does ferment sugar get positive reaction. Add up scores and type into database give this info.
What are three things needed to be pathogenic (general)
Colonisation - attachment
Evasion
Damage via toxins and invasins
What do the surface proteins do
Allow colonisation of skin
Apart from streptolysins and streptokinase what other enzyme is produced
Hyularonidase
What are the toxins that lead to inflammation inducing temp
Streptococcal pyrogenic extoxins (SPE)
What does F protein do
Recognise fibronectin on ECM.
Primary attachment to pharynx and skin
Facilitates internalisation to enter epithelial cells
What is gas f protein process
Group A strep bound to f protein
This bind to fibronectin and get internalisaed
Can be phagocytosis/lysozyme
M protein then used to get tighter binding
What do M proteins protrude in the form of
Fimbrae and pilli
What must M protein go through to extrude as pili
Bound to cytoplasmic membrane, go through peptidoglycan and group antigen (polysaccharide)
How many immunological types are there and is reinfectiuon hence common or rare
Excessing 80 types so common reinfection
What is distinct about the structure of M proteins
Similar to some of our tissues, heart, kidney, muscle, skin
Risk of autoimmunity
What key functions does m protein do
Attachment
Bind serum proteases - spread through tissue
Antiphagocytuc - prevent c3b binding complement
How does it evade our immune system
Hyalurnic acid capsule - we have hyaluronic acd in our ECM so hides. Also bind CD44 which have a lot of in system. Can attach using CD44
Immunolglobulin binding protein - bind to fc region of IgA and IgG preventing opsonisation
C5a peptidase - inactivate c5a (reduce neutrophil recruitment)
What virulence factors does it secrete
Strep o - MW 60,000. Lysis RBC, pore forming, type II toxin, highly antigenic (produce antibodies to it called streptolyosin o eaters can measure in patients)
DNAase - A,B,C,D (b mist common strep) - split DNA use to grow
Streptokinase - antigen secreted by strep combine with plasminogen to form plasmin - hydrolyse fibrin clot - spread
Hyalurondase - movement
SPE’s
Which virulence factor used clinically and how
Streptokinase - catheter break down clot
Where does streptococcal pyrogenic exotoxins bind
Membrane outer
What is a superantigen
Antigen get massive cytokine release as doesn’t need to be digested and presented on MHC II - non specific binding so many more T cell binding so more TNFa
What does immunologically mediated disease mean
Disease due to our antibodies attacking bacteria e.g. Rheumatic fever
What are 4 types of disease strep and name infections for each
1- superficial - impetigo, vaginitis
2- deep - septicaemia , gangrene
3- toxin mediated - scarlet fever
4- immuno mediated - rheumatic fever
Describe impetigo infection
Initial papulovesicular lesion surrounded by redness
Vesicles rapidly become purulent - covered thick honey coloured crust
- lesions mostly on face
- may resolve within 1-2 weeks but often spread to rest of body
Common preschool children, mental institution
What is a predisposing factor to impetigo
Bad hygiene
What other organism can cause impetigo and what is important vabout infection
Staph
Spread through cough and touch
Where does gangrene occur
Subcutaneous tissue (fascia)
Describe a gangrene infection
1- initial trauma
2- 48-72hr - skin purple and blisters containing yellow or haemorrhagic fluid appear
3- day 4 - gangrene present - sloughing of skin
4- day 7-10 - skin break down - necrosis subcutaneous tissue. Need surgical debridement to save life
Describe first stage of scarlet fever (tonsillitis - strep throat)
Pain, erythema, temp, pus
Colonisation followed by inflamed throat ad release of pyrogenic exotoxins (A,B,C,F)
Describe scarlet fever
If strep A tonsillitis not treated can get scarlet fever
Rash appear 12-72 hrs after fever
Spread via coughing, sneezing
Children - 5-15 years
Symptoms:
Sore throat, fever over 38 deg
Widespread rash - torso and arms and legs.
White strawberry tongue/ red strawberry tongue
How many strep throats go to SF
10%
Describe the autoimmune disease RF following strep infection
Antibodies produced to GAS M protein and nag cross react human myosin, tropomyosin, laminin and keratin
1-4 weeks post strep infection, associated with M types 1,3,5,6,18,24
Inflammation of joints, heart, CNS, skin
Describe other immunologically mediated post strep disease
Glomerulonephritis - affect kidney
3 week post strep assocuiated M types (partiularly) 12, 4,2, 49
Symptoms ; swelling of face, haematuria, fluid balance irregularity
Pathogenesis: deposition immune complexes in glomeruli (basement membrane)
Cross reacting antibodies to GAS and glomerular antigens
