Streptococcal infections are caused by Streptococcus bacteria, which are gram-positive spherical or oval-shaped cocci that are often arranged in chains. They contain antigens like capsules and enzymes. Acute infections can cause suppurative lesions in the respiratory tract or skin, while non-suppurative lesions can result in rheumatic fever or glomerulonephritis. Diagnosis involves detecting the bacteria through gram staining, culturing on blood agar to see beta hemolysis, or testing for increased antibodies through tests like the ASO test or skin test for susceptibility to scarlet fever.

1. Streptococcal Infections

2. Streptococcus
Gram positive
Spherical
Oval shaped
Arranged in chains of varying lengths mostly diplococci

3. Antigenic structure
Hyaluronate capsule
Hyaluronidase enzyme
Group speci
fi
c polysaccharide antigen
T
ype speci
fi
c antigen
T
oxins - Hemolysin and Erythrogenic toxin
Enzymes - Streptokinase, Streptococcal
deoxyribonuclease and hyaluroninase.

4. Suppurative lesions
Acute infection of respiratory tract e.g. Sore throat.
Erysipelas - acute
fi
bril disease with localised in
fl
ammation and
redness of the skin and sub cutaneous tissue.
Cellulitis - in
fl
ammation of cell and connective tissue.

5. Non-suppurative lesions
Acute rheumatic fever
Acute glomerulonephritis

6. Lab diagnosis
Haematological investigation
Increase in total leukocyte count
DLC shows increase in neutrophil more than 80%
ESR shows increase in case of rheumatic fever

7. Bacteriological investigation
Gram positive cocci in chains is indicative of streptococcal
infection
Specimen is inoculated on blood agar medium and incubated at
37 c for 18-24 hours
Colonies are circular low convex with a zone of beta hemolysis
around them

8. Serological tests
ASO test - T
o check rheumatic fever - 200 units or more raised
of titre is evidence.
Skin test - T
o check the succeptibility of the patient to scarlet
fever- 0.2 ml erythrogenic toxin is injected intradermally- after
24 hrs generalised skin rash then skin test is positive.