Genus: Streptococcus - labalbaha



Genus: Streptococcus

Definition:

It is gram positive cocci (single cell is spherical) non motile, some strains are capsulated, non spore forming arranged in chain or in pairs. Catalase negative, all are aerobic or facultative anaerobic organism. Ferment CHO with production of acid but never gas.

Normal Habitat:

* Streptococci form a part of the normal flora of man and animals. They inhabit in various sites.

* It may found in upper respiratory tract, and usually live harmlessly as commensals.

* Enterococci form a part of the normal flora of the intestinal tract of Man. S. agatactiae found in G.T of female.

* Some time found in water vegetable, milk and milk product.

Classification of streptococci:

1- Based on haemolytic activity:

When the organism cultured or cultivated on blood agar and incubated at 37C over night under aerobic condition in presence of 10 % CO2, streptococci species can be classified as follows.

i. Beta-haemolytic streptococci (Complete haemolysis):

Colonies are surrounded by a clear zone of complete haemolysis (haemolysis is more marked when the plate has been incubated an aerobically. E.g. S.pyogene and S.agalactiae.

ii. Alpha. Haemolytic streptococci (partial haemolysis).

Colonies are surrounded by a zone of partial haemolysis with green –brown color (reduce of hemoglobin) S.viridance & S.pneumonia.

iii. Gram- haemolytic streptococci (Non- haemolytic):

Colonies show neither typical alpha-non beta haemolysis e.g. S.faecalis

2- This organism also classified by Borgy's in family family deinococcaceae, genus streptococcus. Also classified in to many species e.g:

S.pyogenes

S.agaltactae

S.pheumonia.

S. viridance

S. faecalis (Enterococcus).

3-

4- Lancefield grouping:

ß- haemolytic streptococci produce group specific CHO known as "C" carbohydrate found in the cell wall, that can be identified using group specific antisera from (A-H), (R-U).The most important streptococci belongs to group A streptococci, other pathogenic streptococci belongs to grpups B, C, D, F & G.

* Antigenic structure:

1- capsule: It is made up of hyaluronic acid, it is non immunogenic, and have only a weak an antiphagocytic action, produce by streptococci in the early stage of artificial culture and also when spreading in blood and tissues .

2- Cell wall antigens, they are M, T and R antigens. M. protein is type specific (used in typing) and it has high antiphagocytic action and so very important in virulence.

3- Group specific carbohydrate: contains the group specific (antigen, used in Lancefield grouping, (also in serological test).

4- Cytoplasmic membrane contains antigens not exposed on the surface of the intact cell.

5- Fimbriae on the surface of streptococci enable attachment to epithelial cells and consist of M. protein.

* Toxin and Enzyme produce by streptococci:

1- Streptolysin O:

Toxin that haemolyze red blood cells under reduce condition ( anaerobic condition), It is immunogenic protein, stimulate the production of antibodies (Antistreptolysin O) (ASO). That can measure in proteins serum.

2- Streptolysin S:

Toxin that haemolyze red blood cells, That active aerobically cause ß. haemolysis on blood agar, non immunogenic.

3- Streptokinase:

A protease enzyme that lysis fibrin (Fibrinolysis).

4- Hyaluronidase:

Facilitate spreading in tissue by destroying hyaluronic acid in connective tissue (antigenic enzyme).

5- Leucocidin:

Destroys leucocytes (WBCs).

6- DNAse:

A, B, C & D, which break down DNA and stimulate an antibody response.

7- Erythrogentic toxin:

Responsible for the rash seen in scarlet fever and is also associated with toxic shock syndrome, they are three type A, B and C (SPE).

* Pathogenicity:

1- S.pyogenes (Lancefieled group A) cause.

▪ Sore throat (Tonsilitis, pharyngitis).

▪ Peritonsillar abocess.

▪ Scarlet fever.

▪ Otitis media.

▪ Puerperal sepsis.

▪ Septicaemia and occasionally toxic shock syndrome.

▪ Post-streptococcal rheumatic fever.

▪ Rheumatic heart disease.

▪ Necrotizing fascitis.

2- S.agalactiae (B):

▪ Cause septic abortion and puerperal or gynecological sepsis.

▪ Occasionally U.T.I.

▪ Rarly case neonatal septicaemia& meningitis.

▪ In cattle cause mastitis.

3- S.pneumoniae:

▪ Cause lobar pneumonia.

▪ Meningitis.

▪ Otitis media and conjunctivitis.

4- S.viridance:

▪ A few spices are pathogenic e.g S.mutans cause dental caries.

5- S. faecalis (Enterocciocci)

▪ Urinary tract infection.

▪ Ulcer paticalabdominal.

▪ Occasional endocarditis and meningitis.

* Laboratory diagnosis:

1. Collection of specimens:

Types of specimens depending on the site of infection (Throat swab, ear swab, blood, CSF… etc).

2. Direct microscopy:

Gram positive cocci, arranged in chain or in pairs or single cell

,non motile, non spore forming& some strains are capsulated (S.pyogenes & S.pneumoniae).

3- Culture:

Cultivate the organism or specimens on blood agar under aerobic and an aerobic condition at 35 – 37oc for 24 hrs. (look for the rustle).

i) ß- haemolytic streptococci:

* S.pyogenes

* S.agalactiae

1. Examine& comment the colonial morphology on blood agar (both are ß- haemolytic).

2. Do gram stain & comment (G+ve cocci chain).

3. Do catalase test (-ve) both.

4. Sentitivity to Baciteracine (S.pyogenes sensitive).

5. Do Lancefield group.

S.pyogenes (group A).

S.agalactiae (group B).

6. Subculture on selective media.

S.pyogenes ( can grow on crystal violet blood agar).

S.agtalctiae (can grow on kanamycin blood agar).

7. Do CAMP test. (Christie Atkins Munch-Petersen)

S.agalactiae +ve.

ii) Alpha-haemolytic streptococci:

* S.viridance

* S.pneumoniae

1. Examine& comment the colonial morphology on blood agar (both are α- haemolytic).

2. Do grams stain & comment (G+ve cocci chain).

3. Do catalase test (-ve) both.

4. Sensitivity to Optochin ( S.peumonia is sensitive)

5. Bile solubility test ( S.peumonia is positive)

iii) Non-haemolytic (Gama):

S.faecalis (D) (Enterococci).

1- Examine the colonial morphology on blood agar.

2- Do gram stain& comment (G+ve cocci) chain).

3- Do catalase test (-ve).

4- Do Asculine hydrolysis (+ve) produc black colonig.

5- Heat resistant test (60oC for 30 min).

6- Litmus milk decolorization test (+ve).

7- Culture on Mac-conkey agar (can grow and produce small drak-red colonies (magenta color) and produce yellow colonies on C.L.E.D.

8- Lancefield group (group D).

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