for mbbs 2nd prof

1. STREPTOCOCCUS
It is gram positive cocci which are arranged in chains. They are part of normal human flora.
CLASSIFICATION –
A. Alpha haemolytic streptococci
B. Beeta haemolytic streptococci
C. Gamma or non haemolytic streptococci
MORPHOLOGY –
- Spherical or oval
- Diameter 0.5 to 1 micro meter
- Non motile
- Non sporing
- Capsule - group A & C (hyaluronic acid), group B&D (polysaccharide)
CULTURE –
- Aerobes & facultative anaerobes
- Temp – 22 – 42 degree
- Optimal temp. – 37 degree
- Grow poor in nutrient agar
- Good growth occur in media containing blood, sugar or serum.
- Crystal violet blood agar medium is used for isolation of strept. Pyrogenes.
- Colony – circular, small 0.5 to 1 mm pin point, semitransparent, low convex, wide zone of
beeta haemolysis.
BIOCHEMICAL REACTIONS –
- Catalase – negative
- Failure to ferment ribose which is useful to differentiate from staphylococcus.
- Hydrolysis of pyrrolidoniyl naphthalamide (PYR TEST)
- Several sugars are fermented by it producing acid without gases.
- Resistance to SXT antibiotics
ANTIGENIC STRUCTURE –
- Capsule hyaluronic acid
- Group specific polysaccharide antigen
- Type specific antigen

2. M – protein
T & R protein
Other associated factors
TOXINS -
- Haemolysins – it produce two type of haemolysins, streptolysin ‘O’ & ‘S’. they are produced
by group A, C and G. streptolysin O is oxygen and heat labile. It lyses red cells and it is also
cytotoxic for neutrophils and cardiac tissue. Streptolysin S is oxygen stable haemolysin and
is responsible for the haemolysis seen around colonies of streptococci on the surface of
blood agar plate. It also have leucocidal action.
- Pyrogenic exotoxin – This toxin is responsible for the rash of scarlet fever. It is only
produced by lysogenic strain of group A streptococci. Three types A,B and C have described.
Types A and C are coded for by bacteriophage genes but type B gene is chromosomal. It
causes pyrogenecity cytotoxicity and enhancement of susceptibility to endotoxin.
ENZYMES –
- Streptokinase
- Hyalurinodase
- NADase
- Deoxyribonuclease
PATHOGENESIS –
Streptococcus Lesions
Str. Pyogenes
(1) Pyogenic infections
Respiratory infections Acute tonsillitis or pharyngitis, scarlet fever
Skin infections Infections of wounds, burns and skin lesions,
erysipelas, impetigo
Genital infections Puerperal sepsis
Deep infections Bone and joint infections, lymphadenitis,
septicaemia, abscess in internal organs
(2) Non suppurative complications Rheumatic fever, acute glomerulonephritis
Group B streptococci Neonatal infections (septicemia & meningitis)
Enterococcus faecalis Urinary tract infections
Endocarditis
Viridans srteptococci Endocarditis
Dental caries

3. LAB DIAGNOSIS –
1. Specimen – Swab, Pus, Blood and CSF
2. Collection & transport – collected in sterile container, transported in Pikes transport
medium.
3. Gram staining of smear - Gram positive cocci which are arranged in chains.
4. Culture, colony, morphology and staining – culture in blood agar. for others see above.
5. Biochemical reactions – see above
6. Lancefield grouping – haemolytic streptococci are grouped serologically by lancefield
technique. It is done for definite classification and epidemiological studies. It depends on C
carbohydrate which is specific for each group. C carbohydrate is extracted from the cell wall
of streptococci and grouping done by a precipitation test with group antisera.
7. Antigen detection test – Elisa and agglutination test are used.
TREATMENT – PENICILLIN G
See differentiating features of acute rheumatic fever & acute glomerulonephritis.