MI - M5 - Gram-Positive Pathogens Streptococcus Pyogenes

What is a-haemolysis?

Oral or viridans streptococci

- Partial hemolysis or blood agar plates

- S.pneumonia

- Most oral streptococci

GREEN

What is B-haemolysis? Not key

Pathogenic streptococci

- Complete hemolysis on blood agar plates

- S,pyogenes and anginosus group of oral streptococci

Clear haemolysis

What is Haemolysis? Not key

Is the destruction of red blood cells (erythrocytes)

- How to identify streptococcus

What is y-harmolysis?

Enterococci

- No hemolysis of blood agar plates

- Enterococcus faecals

No Haemolysis

What is Group A Streptococcus as a reference to?

Numerous types of associated diseases

- Most significant pathogenic streptococci

How are Streptococcus pygoenes identified? (Pharyngitis or streptococcal sore throat, scarlet fever)

- Gram +ve cocci

- Chains = Liquid media

- Catalase negative

- Haemolysis

* GAS = B haemolysos (S.pyogenes, bacitracin sensitive)

What is the pathology of Streptococcus pygoenes? (Pharyngitis or streptococcal sore throat, scarlet fever)

- Skin infections

- Upper respiratory tract infections

- Rheumatic fever = Heart

- Glomerularnephritits

What does the origin of Group A refer to?

To antibodies raised to the surface carbohydrates

- Subdivided according to M protein antigens

What is the reservoir in the Oropharynx?

- Very complex microflora

- Contains organisms found in the nasopharynx plus others such as mycoplasma spp. and B-haemolytic streptococci

- Dominated by a-haemolytic streptococci

How is streptococcus pyrogens similar to staphylococci?

Flexible with multiple virulence factors

What are the main diseases associated with streptococcus pyrogens?

- GAS Skin disease

- Invasive GAS Diseases

- Classical Strep Throat

- Sore Throat

- Bacterial Sore throat

- GAS specific diseases

- Rheumatic fever

What is GAS Skin diseases?

Pathogens that cause skin infections and can present in mouth and throat (Uncommon to have a cough, minus bacterial sore throat)

What is Invasive GAS Diseases (iGAS)?

- Impetigo, cellulitis = Invasive strepto A strains penetrate the mucous membrane and develop in lesions

- Necrosting factor (Type 2) = Rapidly destroys connective tissue

- Acute stepto gingivitis

What is classical strep throat?

Bacterial infection from pharyngitis to tonsillitis

What is sore throat?

Viral pharyngitis "Strep throat"

What is bacterial sore throat?

Pharyngitis>Tonsillitis

- Abscence of fever

- Coryza = Inflammation of nasal mucous membranes

- Cough (Uncommon in GAS)

What is GAS specific diseases?

What is rheumatic fever?

- Autoimmune diseases = Increased risks of infective endocarditis

- Delayed reaction due to inadequate recovery from GAS

What are the identifications of streptococcus pyogenes?

- Gram +ve cocci

- B-haemolysis, bacitracin sensitive

- Group A carbohydrate

- Typed by M proteins

- Toxins (SLS, iGAS, Scarlett fever)

What are the pathologies of streptococcus pyogenes?

- Skin conditions

*Impetigo, cellulitis, necrotising fasciitis

- Pharynx

* Strep sore throat

* Scarlett fever

* Acute streptococcal gingivitis

- Autoimmune diseases

* Rheumatic fever

* Glomerular nephritis

What are the 3 antibiotic treatments?

GAS still relatively sensitive to antibiotics but erythromycin resistance growing

- Penicillin V = 10 day course

- Amoxicillin = Acceptable to children

- Erythromycin = Patients sensitive to penicillin

4 defences of the upper respiratory tract defence?

- Mechanical washing

- Cough response

- Mucociliary clearance

- Microbiotica/flora

What are the 3 infectious organisms in the respiratory tract?

- Bacteria

- Viruses

- Fungi

What does M protiens help diseases?

Attach to the upper throat

- Fibronectin and specific binding sites

What is streptolysin (SLS) (Hae

- Tissues/Cell destruction

- Pore-forming cytolysin

- Toxin to PMN, organelles, platelets

- Important in animal models

What are key in proteins for the colonising throat?

Surface proteins = Needed for adhesion in:

- Oropharynx and nasopharynx

- Non ciliated cells covered in mucus

- Range of adhesins

What are these in relation to the colonisation of the pharynx and skin?

- M protein

- Hyaluronic acid = Capsule

Key surface proteins for adhesion

- M proteins = Fibronectin and specific binding sites

- Hyaluronic acid = Capsule, CD44 +ve Keratinocytes

Example of evasion of host defences?

- Protease = Cleaves immunoglobulins

- Cleaves C5a = Cleaves at PMN binding site and hinders their activation

- Binds C5b and C7 = Cleaves at membrane insertion site

Summary - What leads to strep throat and GAS diseases?

- Virulence factors

- M proteins

- Capsule

- SLS

- Exoproteins

- STST

- Tissue invasion

* Treatment = Hopefully self limiting