Lec.3 Genus: Streptococcus Streptococci are Gram positive spherical cocci. Classification of Streptococci The classification of Streptococci has been based on: The classification of Streptococci has been based on: Colony morphology and hemolytic reactions on blood agar. Serologic specificity of the cell wall or capsular antigens. Biochemical reactions and resistance to physical and chemical factors. Ecological features.

1.Hemolysis a.Complete disruption of erythrocytes with clearing of the blood around the bacterial growth is called β hemolysis. b.Incomplete lysis (α hemolysis) of erythrocytes with reduction of hemoglobin and the formation of green pigment. c.Non hemolytic (γ hemolysis) streptococci. c.Non hemolytic (γ hemolysis) streptococci. 2. Group-specific substance (Lancefield classification). The carbohydrate substance is present in the cell wall of many Streptococci and form the basis of serologic grouping into Lancefield groups A-H, and K-U. Typing is generally done only for groups A,B,C,F and G which cause disease in humans. The carbohydrate substance is present in the cell wall of many Streptococci and form the basis of serologic grouping into Lancefield groups A-H, and K-U. Typing is generally done only for groups A,B,C,F and G which cause disease in humans. 3.Capsular polysaccharide The antigenic specificity of the capsular polysaccharide is used to classify: The antigenic specificity of the capsular polysaccharide is used to classify: a.Strept. pneumoniae into over 90 types. b.Group β Streptococci (S. aglactiae). 4. Biochemical reactions

Streptococcus pyogenes 1.Most Streptococci that contain the group A antigen are S. pyogenes. 2.is the main human pathogen associated with local or systemic invasion and poststroeptococcal immunologic disorders. 3.produces complete hemolysis of blood (β hemolysis) around the colonies with more then 0.5mm in diameter. 4.They are PYR- positive (hydrolysis of L- pyrroldionyl -2- naphthlamide) and are susceptible to bacitracin. Morphology and identification A.Typical organisms a.The cocci are spherical or ovoid and are arranged in chains. They divide in plane perpendicular to the long axis. b.Most group A strains produce capsules composed of hyaluronic acid. Capsule of other Streptococci (S. pneumoniae and S. agalactiae) are different. c.The cell wall of S. pyogenes contains proteins (M,T,R antigens), carbohydrate (group specific) and peptidoglycans.

B.Culture Most Streptococci grow on solid media. Strept. pyogenes is β hemolytic, other species have variable hemolysis. C. Growth characteristics a. Growth of Streptococci on solid media or broth is poor unless enriched with blood or tissue fluids. b. Growth and hemolysis are enhanced by incubation in 10%Co 2 c. Most Streptococci are facultative anaerobes. Peptostreptococcus are obligate anaerobes.

Antigenic structure A. M protein B. Group specific cell wall antigens C.T. substance D.Nucleoproteins (p- substance).

Toxins and Enzymes More than 20 extracellular products that are antigenic are elaborated by S. pyogenes. 1. Streptokinase (fibrinolysin). 2. Streptodornase (Streptococcal deoxyribonuclease, DNA ase). 3. Hyaluronidase (spreading factor) 4. Erythrogenic toxins (pyrogenic exotoxins) 5. Hemolysins a. Streptolysin S b. Streptolysin O 6.Diphosphopyridine nucleotidaes

Clinical diseases due to S. pyogenes. Clinical diseases due to S. pyogenes. 1.Diseases due to invasion by S. pyogenes. a.Erysipelas: If the portal of entery is the skin, results with massive brawny edema and a rapidly advancing margin of infection. a.Cellulitis: Is an acute, rapidly spreading infection of the skin and subcutaneous tissue.

c.Necrotizing fasciitis (streptococcal gangrene) infection of the subcutaneous tissue and fascia. There is extensive and repid spreading necrosis. c.Puerperal fever If the streptococci enter the uterus after delivery, puerperal fever develops, which is essentially a septicemia originating in the infected wound (endometritis). c.Bacteremia /sepsis Infection of traumatic or surgical wounds result in bacteremia which rapidly can be fatal.

2.Diseases due to local infection with S. pyogenes and their by- products. a.Streptococcal sore throat The organism adhere to the pharyngeal epithelium by a lipoteichoic acid- covered pill. In infants and small children, the sore throat occurs as a subacute nasopharyngitis with a thin serous discharge and little fever, In older children and adults, the disease is more acute and characterized by intense nasopharyngitis tonsillitis, and intense redness and edema of the mucous membrane, with purulent exudates, enlarged cervical LN and high fever. In 20% of the infections are asymptomatic. In older children and adults, the disease is more acute and characterized by intense nasopharyngitis tonsillitis, and intense redness and edema of the mucous membrane, with purulent exudates, enlarged cervical LN and high fever. In 20% of the infections are asymptomatic. b.Streptococcal pyoderma Local infection of superficial layers of skin especially in children, is called impetigo Group A skin infection are attributable to M types 49,57,59-61 and may preced glomerulonephritis, but not lead to rheunative fever.

3.Invasive group A Streptococcal infections a.Streptococcal toxic shock syndrome. Fulminant, invasive S.pyogenes infections are characterized by shock, bacteremia, respiratory failure,and multi-organ failure. Death occur in 30% of the patients. The infection tends to follow minor truma or soft tissue infection as necrotizing fasciitis. Bacteremia occur frequently. The infection tends to follow minor truma or soft tissue infection as necrotizing fasciitis. Bacteremia occur frequently. b.Scarlet fever Occur in association with S. pyogenes pharyngitis or with skin or soft tissue infection by strains producing exotoxins A (erythrogenic toxin). The rash appears on the trunk after 24hrs. and spread to involve the extremities with straw-berry tongue. accompanied by fever

4.Post streptococcal diseases (rheumatic fever, glomerulonephritis) a.Both diseases occur after acute S. pyogenes infection. b.The post- streptococcal disease are not attributed to the direct effect of disseminated bacteria but represent a hypersensitivity response. c.Nephritis is mostly preceded by infection of the skin, while rheumatic fever mostly preceded by infection of the respiratory tract.

A. Rheumatic fever  Is the most serious disease of S. pyogenes because it results in damage to heart muscle and valves.  Caused by strains contain cell membrane antigens that cross-react with human heart tissue antigens, and the sera of patients (pts). With rheumatic fever contain antibodies to these antigens.  The pts. with more severe Streptococcal sore throat have a greater chance of developing rheumatic fever.  Rheumatic fever preceded by S. pyogenes infection 1-4 weeks earlier.  The main symptoms and signs are fever, malaise and evidence of inflammation of all parts of the heart.  The carditis leads to thickened and deformed valves and to a small perivascular granuloma in the myocardium (Aschoff bodies) that are replaced by scar tissue.

B.Acute glomerulonephritis  Develops 3 weeks after S. pyogenes skin infection (pyoderma, impetigo).  Caused by strains that are nephritogenic, principally with M types 12,4,2,49, and  The incidence of nephritis is less than 0.5%.  Glomerulonephritis initiated by antigen-antibody complexes on the glomerular basement membrane.  Not reactivated by recurrent infection.  In acute nephritis, there is blood and protein in the urine, edema, high blood pressure. A few pts. die, some develop chronic disease and the majority recover completely. A few pts. die, some develop chronic disease and the majority recover completely.