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Streptococci

Streptococci. Gehan J. Panagoda Division of Microbiology. Morphology. Gram +ve, chains, diplo, initially from erysipelas, divisions one plane, mention about Staph, length of chains varies on culture conditions. No relationship between length and virulence.  haemolysis. Strep and pus.

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Streptococci

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  1. Streptococci Gehan J. Panagoda Division of Microbiology

  2. Morphology • Gram +ve, chains, diplo, initially from erysipelas, divisions one plane, mention about Staph, length of chains varies on culture conditions. No relationship between length and virulence

  3.  haemolysis Strep and pus Cervical lymph adenitis Tonsilitis

  4. Culture • Aerobes, facultatively anerobic, pathgenic Strep require exacting nutrients. Therefore, grow well in BA. 10% CO2 promotes growth and haemolysis.

  5. HaemolysisAlpha, partial with greenish discolouration (unidentified reductant haemoglobin - viridans strep and pneumococcus (NO SUCH THING CALLED STREP. VIRIDANS). Beta, a wide clear zone, beta haemolysins - Streptolysin O and S - S. pyogenes. Gamma - non-haemolytic (commonly used term) - S. faecalis.

  6. Classification • For aerobic and facultative anaerobic • .Haemolytic classification • I have already mentioned about this. Most of the pathogenic Strep causing primary infections fall into beta. Alpha Strep is generally remains as commensals.

  7. .Serological classification - For beta haemolytic Strep • 1. Based on the group specific polysaccharide (c) antigen of the cell wall - Lancefield classification, 20 A-V, No I and J. THE MOST IMPORTANT GROUP IS A - S. pyogenes.

  8. 1.1 Based on the type specific antigen (M, T, R most important is A - Mass Transit Railway) - forS. pyogenes serotyping - Grifith classification - 80 serotypes. M is on the cell, resists phagocytosis, promotes adherence to the host. WITHOUT M IS AVIRULENT.

  9. .Classification based on Schleifer and Kilpper-Balz (1987) -Based on the structure of the cell wall and G + C composition (NOT IMPORTANT FOR YOU).

  10. S. pyogenes • PATHOGENIC FEATURES - 1. M that is the type specific antigen 2. Capsular hyaluronic acid - capsule also in gp C during the logrithmic phase. ANTIBODIES PRODUCED AGAINST THE CAPSULE IS NOT PROTECTICE.

  11. MEANS THE CAPSULE IS A VIRULENT FACTOR, SIMILAR TO THAT OF PNEUMOCOCCUS, INHIBITS PHAGOCYTOSIS

  12. 3. Toxins and enzymes Toxins - Streptolysin S and O - have already mentioned. Streptolysin O acts not only against red cells but also cytotoxic to neutrophils and platelets and cardiac tissue. An ASO titre of 160-200 units - suggests a recent infection. Erythrogenic toxin - the rash of scarlet fever.

  13. Enzymes • Streptokinase - lyse RBC, prevents a fibrin barrier around the leision thus spread • Nicotinamide adenine dinucleotidase (NADase)

  14. Hyaluronidase - acts on hyaluronic acid - antibodies against this is diagnostic. THEREFORE, ASO AND THIS IS IMPORTANT IN DIAGNOSIS OF S. PYOGENES INFECTIONS

  15. .Suppurative infections • Acute infections of the respiratory tract. Sore throat-(acute tosillitis/and or pharyngitis - organisms are at the site - can spread and cause cervical adenitis, otitis media, meningitis. Scarlet fever- a complication of sore throat, rash is due to erythrogenic toxin, organism is not at the site.

  16. Skin infections - Impetigo - among children, discrete infections, highly communicable, common in countries like Sri lanka (Why ? hot and humid). Organism is at the site. Can cause also by Staph. aureusErysipelas mainly among elderly - acutely spreading infection. Some time is associated with sore throat. Organism is present at the site. Believed to be a hypersensitivity reaction.

  17. Erysipelas - Butterfly-wing rash • Followed by upper • respiratory tract infection • On the face or leg • Transferred by fingers

  18. Scarlet fever Caused by an erythrogenuc strain Portal of entry is the throat May followed by infection of wound/burn

  19. Pathogenesis • (Immune mechanism) Ab produced against protein and polysaccharide of orga cross react with myocardial and heart valve tissue Not clear. • Immune response Marked ASO titre  200 Moderate to low • Course Progressive Spontaneous resolution • Penicillin • Prophylaxis Because of repeated attacks, Penicillin • Prophylaxis is Essential Not indicative

  20. .Laboratory diagnosis • .Acute suppurative infections • Smear - Strep and pus; Culture - in a transport medium, on BA 370C ,  haemolysis, overnight, better under anaerobic with 5-10% CO2, ELISA to detect Strep antigens, Serological tests - not useful

  21. .Non-suppurative complication • Culture - useful for the presence of Strep/ serological test to check the level of ASO titre  200 for rheumatic fever, DNAase-B test for acute nephritis

  22. .Other haemolytic Streptococci • Group B -S. agalactiae - bovine mastitis, neonatal septicaemia and meningitis • Group C and G • ENTEROCOCCI - Group D • STREPTOCOCCUS MILLERI (UK term) in USA (S. intermedius) (Group F) alpha, beta of gamma, present in the mouth, throat GI tract, infect internal organs, brain liver,

  23. Suacute bacterial endocarditis • Splinter haemorrhages • Lodging of emboli under finger nails • other than kidneys and brain

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