Streptococcus pyrogenes
Beta haemolysis;Group A
Morphology
Spherical or oval shape
0.5- 1.0 micrometre in diameter and are arranged in chain.
Chain formation due to streptococci divide in one plane without separating.
Source and Modes of Transmission
Organism resides on skin and mucus membrane act as major source to transmit the infection.
Produce haemolysin exotoxin;
Streptolysin O
Streptolysin S
Pathogenesis and clinical significance (Disease)
1. Acute Rheumatic fever
2. Respiratory sore throat (tonsillitis/ pharyngitis)
3. Sepsis; infection of skin lesions
4. Streptococcal toxic shock syndrome (entire organ collapse, cause death)
5. Skin and soft tissue Infection
6. Puerperal sepsis; Infection after just delivery of new born.
7. Lymphangitis and cellulitis
8. Erysipelas; large raised patches on the skin
9. Impetigo
Symptoms
Sore throat
Swollen lymph nodes in neck
Fever
Swollen tonsil
Bad breath
Laboratory Diagnosis
1. Specimen collection
Take throat swab, pus swab, sputum
2. Collection and transport
3. Gram staining of smear
Presence of gram +ve cocci
4. Culture
It is aerobic and facultative anaerobic.
Best grow at 37 degree Celsius in presence of CO2 which enhance hemolytic.
Growth occur only enrich media containing blood or serum.
5. Colony morphology and staining
6. Biochemical reaction
Colonies of streptococcus pyogenes lactose, glucose, maltose produce acid and no gas.
It doesn't ferment ribose simple sugar produce by human body.
7. Identification of various group of streptococci
8. Serological test
(Antitreptolysin O)ASO titers test; use to detect antibody
Anti - DNase B ADB titers test; for skin infection
Prevention and Treatment
Rheumatic fever is prevented by rapid eradication of infectious organism, prolonged antibiotic therapy should be used.
Penicillin G drug is used.
In patient allergy to penicillin, erythromycin or cephalexin is used.
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