STREPTOCOCCI By Eric S. Donkor

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

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

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

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

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

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

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

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

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

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

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

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

Pathogenesis of Streptococcus pneumoniae Polysaccharide capsule is the main virulence factor

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

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)

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

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

Identification of Streptococci

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

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.

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

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

Viridan streptococci Penicillin usually used