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STREPTOCOCCI By Eric S. Donkor.

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1 STREPTOCOCCI By Eric S. Donkor

2 Morphology and characteristics
Cocci cells arranged in chains Gram positive cell wall with C- carbohydrate in some streptococci Protein antigens e.g. proteins M and T Presence of capsule in some species Some form part of the normal flora Most are facultative anaerobes Usually require enrichment for growth Non motile and non-sporing

3 Classification Haemolysis- alpha, beta, gamma
Serological specificity of antigens C- carbohydrate (Lancefield classification) Capsular antigens Cell wall protein antigens Biochemical reactions

4 Pyogenic streptococci (Lancefield groups)
Groups A, B, C, F, and G are associated with human infections Groups A and B of the greatest pathogenic significance

5 Streptococcus Group A (Streptococcus pyogenes)
Group specific antigen is Rhamnose N-acetylglucosamine Found on the skin and in the throat Beta-haemolytic Capsule of hyaluronic acid Produces extracellular toxins and enzymes M protein enables classification into over 80 serotypes M protein associated with virulence and type specific immunity

6 Pathogenesis of Streptococcus pyogenes
Attachment to epithelial cells Resistance to phagocytosis Extracellular toxins and enzymes

7 Diseases of Streptococcus pyogenes
Pharyngitis Skin infections Impetigo Erysipelas Cellulitis Wound infections Puerperal infections Toxin mediated diseases Scarlet fever Toxic shock syndrome Post streptococcal diseases Acute rheumatic fever Acute glumerulonephritis

8 Laboratory diagnosis of Streptococcus pyogenes
Specimen: throat swab, pus, blood Culture on blood agar plates Blood culture Bacitracin susceptibility Biochemical test (PYR hydrolysis) Detection of group A antigen Diagnosis of poststreptococcal complications by antistreptolysin O antibody

9 Treatment of Group A Streptococcal infections
Highly susceptible to penicillin G Other drugs for treatment include erythromycin cephalosporins tetracycline chloramphenicol Early treatment to prevent post streptococcal diseases

10 Streptococcus Group B (Streptococcus agalactiae)
Group specific antigen is rhmanose glucosamine Normal flora of the female genital tract Beta haemolytic Polysaccharide capsule enable classification into 5 subgroups Ia, Ib, II, III, IV

11 Pathogenesis of Streptococcus agalactiae
Important involvement of: Sialic acid of capsule C5a peptidase

12 Diseases of Streptococcus agalactiae
Neonatal meningitis Neonatal sepsis In adults diseases include cellulitis, arthritis, meningitis No post streptococcal disease

13 Streptococcus pneumoniae (Pneumococcus)
Not part of Lancefield groups Normal flora of the upper respiratory tract Alpha haemolytic Lancet shaped organism usually in pairs Presence of polysaccharide capsule Antiphagocytic Antigenic C- carbohydrate and M-protein in cell wall are also antigenic

14 Pathogenesis of Streptococcus pneumoniae
Polysaccharide capsule is the main virulence factor

15 Diseases of Streptococcus pneumoniae
Meningitis Other infections- otitis media, sinusitis, bacteremia

16 Viridan streptococci C- carbohydrate antigen is not
usually present in this group Normal flora of the upper respiratory tract Alpha haemolytic Very low virulence but can cause disease: subacute endocarditis dental caries (S. mutans)

17 Laboratory diagnosis of Streptococci infections
Specimen include blood, CSF, sputum, swab, pus Type of specimen depends on nature of infection Culture on blood agar plate Gram Stain Observation of colonial morphology including haemolysis Biochemical and serological reactions for further identification

18 Finally I am available for student consultation on bacteriology
My Room no. is 79 in the Red Building

19 Identification of Streptococci

20 Treatment of Streptococci infections
Etiological agents treated are Streptococcus Group A Streptococcus Group B Streptococcus pneumoniae Viridan Streptococci

21 Streptococcus Group A (Streptococcus pyogenes)
Highly susceptible to penicillin G Other drugs for treatment include erythromycin other penicillins cephalosporins tetracycline chloramphenicol Early treatment to prevent post streptococcal diseases.

22 Streptococcus Group B (Streptococcus agalactiae)
Penicillin with an aminoglycoside Other drugs e.g. erythromycin

23 Streptococcus pneumoniae
Penicillin usually used Other drugs: erythromycin chloramphenicol vancomycin Vaccine available for prevention

24 Viridan streptococci Penicillin usually used

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