Group A streptococcal infection

Group A streptococcal infection Microchapters
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Overview
Classification Impetigo Strep throat Rheumatic heart disease Poststreptococcal glomerulonephritis Sinusitis Scarlet fever Tonsilitis Otitis Osteomyelitis Meningitis Brain abscess Endometritis Cellulitis Erysipelas Toxic Shock Syndrome
Pathophysiology

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Ahmed Elsaiey, MBBCH [2]

Overview

Group A streptcocci or streptoccus pyogenes causes a wide range of diseases in many organs in the body. It is important to classify the infections caused by the bacteria in order to understand every disease separately. Classification of the group A streptococcal infections will be based on the pathogenesis of the infection and the organ infected. According to the pathogenesis of the infection, they can be classified into pyogenic, toxogenic or immunogenic infections. Based on the location, the streptococcus pyogenes affects the lungs, ear, nose, throat, blood, female genital system and the central nervous system.

The pathophysiology of the disease depends on various virulence factors. These factors include protein M, streptolysins O and S, hyalourinidase and C5a peptidase.

Classification

Group A streptococcal infections can be classified according to the pathogenesis of the infection and the organ infected. According to the pathogenesis of the infection, they can be classified into pyogenic, toxogenic or immunogenic infections. Based on the location, the streptococcus pyogenes affects the lungs, ear, nose, throat, blood, female genital system and the central nervous system.

Group A streptococcal infections

Pathogenesis

Organ based

Pyogenic

Toxogenic

Immunogenic

Lungs

Ear, nose and throat

Bone

Blood

Female genital system

Brain

Pneumonia

Osteomyelitis

Bacteremia

Pharyngitis (Strep throat)

Cellulitis

Impetigo

Erysipelas

Scarlet fever

Toxic shock like syndrome

Necrotizing fasciitis

Rheumatic fever

Glomerulonephritis

Sinusitis

Tonsilitis

Otitis media

Postpartum endometritis

Vaginitis

Meningitis

Brain abscess

Pathophysiology

Transmission

Group A streptococcal infection can be transmitted by the following:

• Direct inoculation transmission
• Infected airborne droplets

Virulence factors

Group A streptococcus are responsible for various diseases ranging from mild to life threatening cases. The bacteria depends mainly on many virulence factors which are responsible for the pathogenesis of the infections.

Virulence factors	Mechanism of action
M protein	The most important virulence factor. It prevents the phagocytosis of the bacteria by binding to the fibrinogen and prevents binding the complement to the bacterial cell wall.
Streptolysin O and S	Streptolysin O works on killing the differecnt cells like the neutrophils, platelets and the sub-cellular organelles.
Streptococcal pyrogenic exotoxins A and C	SpeA and SpeC are superantigens secreted by many strains of S. pyogenes. These pyrogenic exotoxins are responsible for the rash of scarlet fever and many of the symptoms of streptococcal toxic shock syndrome.
Streptokinase	Enzymatically activates plasminogen which is a proteolytic enzyme into plasmin which in turn digests fibrin and other proteins.
Hyalourinidase	It helps the bacteria to spread through the tissue by destroying the hyaluronic acid which is a connective tissue component.
Streptodornase	Most strains of S. pyogenes secrete up to four different DNases, which are sometimes called streptodornase. The DNases protect the bacteria from being trapped in neutrophil extracellular traps (NETs) by digesting the NET's web of DNA, to which are bound neutrophil serine proteases that can kill the bacteria.
C5a peptidase	C5a peptidase cleaves a potent neutrophil chemotaxin called C5a, which is produced by the complement system. C5a peptidase is necessary to minimize the influx of neutrophils early in infection as the bacteria are attempting to colonize the host's tissue..
Streptococcal chemokine protease	The affected tissue of patients with severe cases of necrotizing fasciitis are devoid of neutrophils.. The serine protease ScpC, which is released by S. pyogenes, is responsible for preventing the migration of neutrophils to the spreading infection. ScpC degrades the chemokine IL-8, which would otherwise attract neutrophils to the site of infection. C5a peptidase, although required to degrade the neutrophil chemotaxin C5a in the early stages of infection, is not required for S. pyogenes to prevent the influx of neutrophils as the bacteria spread through the fascia.

References

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