● Streptococcus pyogenes
○ Characteristics :
■ Gram +ve / cocci in chain / catalase ve
■ Group A Beta hemolytic streptococci
● All beta hemolytic streptococci are classified by two
antigens :
a. C carbohydrate, used for classification of
streptococci, A,B,C,D .. , lancefield
classification.
b. M protein , interfere with phagocytosis and
resembles antigens found on human tissue
(kidney and joints), that's explain why infection
Strep. Pyogenes
with can cause later onset
Rheumatic Fever or
Acute
Glomerulonephritis.
■ Bacitracin sensitive.
■ Colonise the skin.
○ Virulence factors :
■ Polysaccharide capsule : antiphagocytic, composed of
hyaluronic acid, not immunogenic.
■ M protein : antiphagocytic.
■ Pili: composed of lipoteichoic acid and M protein.
■ inflammationrelated enzymes :
● (1) Hyaluronidaseis antigenic, degrades
hyaluronic acid, the ground substance of
subcutaneous tissue, is known as spreading factor
because it facilitates the rapid spread of Str.
pyogenes in skin infections (cellulitis).
● (2) Streptokinase(fibrinolysin) activates
plasminogen to form plasmin, which dissolves fibrin in
clots, thrombi, and emboli, allowing the bacteria to
escape from blood clots. It can be used to lyse
thrombi in the coronary arteries of heart attack
patients.
● (3) DNase(streptodornase) degrades DNA in
exudates or necrotic tissue, facilitate the spread of
streptococci in tissue by liquefying pus.
■ Toxins and Hemolysins :
● (1) SuperAntigens :
, a. Erythrogenic toxin
■ causes the rash of scarlet fever.
■ It is produced only by certain strains of
Str. pyogenes lysogenized by a
bacteriophage .
■ The injection of a skin test dose of
erythrogenic toxin (Dick test) gives a
positive result in persons lacking
antitoxin.
b. Pyrogenic exotoxin A
■ is the toxin responsible for most cases
of streptococcal toxic shock
syndrome .
■ Coded by lysogenic phage.
■ It has the same mode of action as does
staphylococcal TSST (i.e., it is a
superantigen that causes the release of
large amounts of cytokines from helper
T cells and macrophages
● (2) Streptolysin Ois a hemolysin that is
inactivated by oxidation (oxygenlabile). It causes
βhemolysis only when colonies grow under the
surface of a blood agar plate. It is antigenic
, and
antibody to it (ASO) develops after group A
streptococcal infections. The titer of ASO antibody
can be important in the diagnosis of rheumatic fever.
● (3) Streptolysin S is a hemolysin that is not
inactivated by oxygen (oxygenstable). It is not
antigenic but is responsible for βhemolysis when
colonies grow on the surface of a blood agar plate.
● (4) Exotoxin Bis a protease that rapidly destroys
tissue and is produced in large amounts by the strains
of Str. pyogenes, the socalled “flesheating”
streptococci that cause necrotizing fasciitis .
○ Diseases
:
■ Pyogenic :
● Pharyngitis and
tonsillitis
:
a. Pharyngitis generally develops 2 to 4 days
after exposure to the pathogen
○ Characteristics :
■ Gram +ve / cocci in chain / catalase ve
■ Group A Beta hemolytic streptococci
● All beta hemolytic streptococci are classified by two
antigens :
a. C carbohydrate, used for classification of
streptococci, A,B,C,D .. , lancefield
classification.
b. M protein , interfere with phagocytosis and
resembles antigens found on human tissue
(kidney and joints), that's explain why infection
Strep. Pyogenes
with can cause later onset
Rheumatic Fever or
Acute
Glomerulonephritis.
■ Bacitracin sensitive.
■ Colonise the skin.
○ Virulence factors :
■ Polysaccharide capsule : antiphagocytic, composed of
hyaluronic acid, not immunogenic.
■ M protein : antiphagocytic.
■ Pili: composed of lipoteichoic acid and M protein.
■ inflammationrelated enzymes :
● (1) Hyaluronidaseis antigenic, degrades
hyaluronic acid, the ground substance of
subcutaneous tissue, is known as spreading factor
because it facilitates the rapid spread of Str.
pyogenes in skin infections (cellulitis).
● (2) Streptokinase(fibrinolysin) activates
plasminogen to form plasmin, which dissolves fibrin in
clots, thrombi, and emboli, allowing the bacteria to
escape from blood clots. It can be used to lyse
thrombi in the coronary arteries of heart attack
patients.
● (3) DNase(streptodornase) degrades DNA in
exudates or necrotic tissue, facilitate the spread of
streptococci in tissue by liquefying pus.
■ Toxins and Hemolysins :
● (1) SuperAntigens :
, a. Erythrogenic toxin
■ causes the rash of scarlet fever.
■ It is produced only by certain strains of
Str. pyogenes lysogenized by a
bacteriophage .
■ The injection of a skin test dose of
erythrogenic toxin (Dick test) gives a
positive result in persons lacking
antitoxin.
b. Pyrogenic exotoxin A
■ is the toxin responsible for most cases
of streptococcal toxic shock
syndrome .
■ Coded by lysogenic phage.
■ It has the same mode of action as does
staphylococcal TSST (i.e., it is a
superantigen that causes the release of
large amounts of cytokines from helper
T cells and macrophages
● (2) Streptolysin Ois a hemolysin that is
inactivated by oxidation (oxygenlabile). It causes
βhemolysis only when colonies grow under the
surface of a blood agar plate. It is antigenic
, and
antibody to it (ASO) develops after group A
streptococcal infections. The titer of ASO antibody
can be important in the diagnosis of rheumatic fever.
● (3) Streptolysin S is a hemolysin that is not
inactivated by oxygen (oxygenstable). It is not
antigenic but is responsible for βhemolysis when
colonies grow on the surface of a blood agar plate.
● (4) Exotoxin Bis a protease that rapidly destroys
tissue and is produced in large amounts by the strains
of Str. pyogenes, the socalled “flesheating”
streptococci that cause necrotizing fasciitis .
○ Diseases
:
■ Pyogenic :
● Pharyngitis and
tonsillitis
:
a. Pharyngitis generally develops 2 to 4 days
after exposure to the pathogen
