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Microbiology
- 1. By Dr Hasan Askari Department of pathology streptococci By DR HASAN ASKARI BDS RDS MS MPHIL PHD MJDS MD FDS DDS PRESIDENT OF ROYAL COLLEGE OF EDINBURG V.C OF OXFORD UNIVERSITY ,FATHER OF
- 3. Classification • A Beta haemolytic streptococci: • They cause beta haemolysis (complete haemolysis) on blood agar and have group specific cell wall carbohydrates antigen which give precipitin reaction with specific antisera. On the basis of precipitin reaction they are divided into Lancerfield group A-H and K-U. • Group A : e.g. s. pyogen • Group B: s. agalactiae • Group C AND G: • Group D: enterococci e.g. s. Faecalis • non enterococci e.g. s. bovis • Group E,F,H AND K-U: occur in animals other than human.
- 5. streptococci • B Non beta haemolytic streptococci: • They show alpha haemolysis (incomplete haemolysis ) or no haemolysis. • 1 streptococcus pneumonia (pnemoniae) • 2 streptococcus viridians : • They are alpha haemolytic e.g. • S. Salivarius(group k) • S. Sanguis (group H) • S. Mutans • S. Mitis • 3 group N streptococci: also called lactic streptococci and are non haemolytic.
- 6. streptococci • C Peptostreptococci • They are anaerobic and causes variable haemolysis.
- 8. streptococci • Morphology: • Shape: spherical • Arrangement : arrange in chains or pairs • Division: cocci divide in a plane perpendicular to long axis of chain. • Capsule : some strain are capsulated • Mobility: non mobile • Spore: non spore forming
- 9. streptococci • Staining • Gram staining: • Streptococci are gram positive (appear violet coloured)
- 10. streptococci • Culture • Nutrient agar, blood agar,maconkeys only for (s. Faecalis) • Colonies: • Discoid colonies (1-2mm in diameter) • 1 on nutrient agar small translucent dew drop like colonies. • 2 on blood agar 2 type of haemolysis are seen; • a beta complete haemolysis a clear zone of haemolysis is formed around colonies due to rupture of RBCs with release of haemoglobin. • b alpha incomplete haemolysis a zone of greenish brown discoloration is formed around colonies that contain unlysed RBCs and a green, unidentified. Reduced product of haemoglobin.
- 11. streptococci • 3 on MacConkeys medium s. Faecalis produce small pink colonies. • 4 group A streptococci produce 2 types of colonies: • A matt or mucoid colonies consist of streptococci that produce much M protein. Virulent. • B glossy colonies consist of streptococci that produce little M protein non virulent.
- 13. streptococci • Growth characistics • Oxygen requirements: most streptococci are aerobic and facultative anaerobes. • Peptostreptococci are obligate anaerobes • Energy source is ferment sugar • Temperature streptococci grow at 37degree c • Group d enterococci grow between 15-45 degree c. • 10% co2 promotes growth.
- 14. streptococci • Antigen • 1 group specific carbohydrate antigen • Present in cell wall • Function: • Given precipitin reaction with specific antisera and forms basis for lancefield group A-H and K-u. • Serologic specificity of this antigen is determined by an amino sugar.
- 16. streptococci • 2 M protein • Present in cell wall of organisms producing matt or mucoid colonies. • Function: • Associated with virulence of group A strptococci. • Gives agglutination or precipitation reaction with M protein type specific antisera . • Interfere in phagocytosis. • Causes production of antibodies that acts as opsonion and protect against reinfection .
- 17. streptococci • Other antigen • T substance • R protein • Nucleoprotein • P substance
- 18. streptococci • Enzymes • 1 streptokinase fibrinolysin • Transforms plasmogen into plasmin that digest fibrin and is partially responsible for rapid spread of streptococcal infection by preventing formation of fibrin barrier around the infected site • Clinical use • Give iv pulmonary emboli, venous thromboses.
- 19. streptococci • 2 sreptodornase steptococcal Dnasa • Deploymerises DNA thus help to liquefy exudates and facilitate removal of pus and necrotic tissue. • 3 hyaluronidase spreading factor • Splits hyaluronic acid in ground substance of connective tissue thus hail in spreading of infecting microorganism. • 4 diphosphopyridine nucleotidase kills leukocytes
- 20. streptococci • Toxin • 1 Hemolysins: • Beta haemolytic group a streptococci produce two haemolysin (streptomycin) • A streptolysin O: • 1 causes haemolysis only in anaerobic condition b/c it is o2 labile. • 2 it binds to sterol in host leukocyte membrane where it forms toxin oligomers resulting in large transmembrane pores . This causes release of lysosomal enzymes that results in degranulation and death of leukocytes as well as destruction of adjacent tissues. • 3 suppresses chemotaxis and leukocyte mobility. • 4 it is antigenic and causes production of antistreptolysin o antibodies. • B streptococci S: • 1 Being o2 stable it is responsible for haemolytic zone around streptococcal colonies on blood agar plate. • 2 it is not antigenic • 3 inhibits chemotaxis and phagocytosis.
- 21. Immune system
- 22. streptococci • 2 erythrogenic toxin: • A produced only by lysogenic streptococci. • B possessses two functional parts: • 1 heat labile part , induces fever and suppresses immune system. • 2 heat stable part ,enhances pyrogenicity and produces rash in scarlet fever as a result of hypersensitivity reaction to this part.
- 25. streptococci • Habitat and transmission • Habitat • S pyogene human skin,oropharynx • S agalactiae normal flora of female genital tract. • Group C and G pharynx • Enterococci lower intestinal tract • Viridans normal flora of u.respiratory tract • TRANSIMISSION • Via respiratory droplets
- 27. streptococci • Pathogenesis and clinical findings • A Diseases due to invasion by beta haemolytic group A streptococci. • 1Erysipeles • Caused by invasion of skin. • Clinical finding • massive brawny edema with a rapidly advancing margin of infection. • 2 puerperal fever septicaemia • Caused by invasion of uterus after delivery • 3 sepsis (surgical scarlet fever) • Caused by invasion of traumatic or surgical wound by streptococci.
- 28. streptococci • B disease due to local infection with beta haemolytic group a streptococci • 1 streptococcal sore throat • Caused by attachment of group A streptococci to pharyngeal epithelium by means of lipoteichoic acid covering surface pili. • Clinical finding in kids • Sub acute nasopharngitis with thin serous discharge • Little fever • Enlarged cervical lymph nodes. • Clinical finding in adults • Acute and intense nasophayngitis • Tonsillitis • Intense redness and edema of mucos membrane • Purulent discharge • High fever • Enlarged and tender cervical lymph nodes
- 29. streptococci • Stretococcal sore throat; • 1 scarlet fever rash due to production of erythrogenic toxin. • Quinsy peritonsillar abscess • Ludwigs angina characterized by blockage of air passages by massive swelling of floor of mouth. • Pneumonia occurs by viral infection e.g. influenza or measles • Streptococcal pyoderma (impetigo) local infection of superficial layer of skin. •
- 30. streptococci • Infective endocarditis • Acute endocarditis • In bacteraemia beta haemolytic streptococci settle on normal or previously injured heart valves. • Clinical finding • Acute endocarditis destruction of heart valves, cardiac failure. • Sub acute endocarditis • It involve abnormal valves (congenital deformitis,rheumatic or atherosclerotic lesion).thrombi are formed on injured endothelium of valve leaflets. • Causative organisms • A viridin streptococci reach bloodstream after dental extraction. • Gram negative rods of intestinal flora • Enterococci of gut or urinary tract. • Clinical finding • Fever, anaemia, weakness, heart murmur,emboli,enlarged spleen, renal lesion.
- 32. streptococci • Post streptococcal disease • Occur 1-4 week following an acute group A streptococcal infection • 1 acute glomerulonephritis • It develop 3 week after skin infection with group A streptococci (types 12, 4 , 2 and 49)it is initiated by immune complexes formed by streptococcal antigen and antibodies directed against it. These immune glomerular basement mem.which is damaged by inflammatory reaction. • Clinical finding • Hematuria, proteinuria,edema
- 33. streptococci • Rheumatic fever • It develop 1-4 weeks after sore throat with group A streptococci. It is due to cross reaction b/w human heart antigen and antibodies directed against streptococcal M antigens. As a result , heart valve are damaged.
- 34. streptococci • Clinical finding • Heart: aschoff bodies are deposited in myocardium wart like vegetation on heart valves, fish mouth or buttonhole stenotic deformity of valves,MacCallums plaques on arterial walls. • Joint : migratory non suppurative arthritis. • Skin: subcutaneous nodules, erythema marginatum. • Other fever and malaise.
- 36. streptococci • Other infection • Group B (s agalactiae) • In women bacteraemia and meningitis occur in diabetics and in patient on immunosuppressive drugs • In children born to infected mother bacteremia,pneumonia ,meningitis and sepsis. • Group c and g sinusitis, bacteremia and endocarditis. • Group d: enterococci: UTI endocarditis meningitis • non enterococci: UTI endocarditis • Streptococcus viridan: subacute endocarditis • Streptococcus mutan : dental caries • Group N streptococci: coagulation souring of milk
- 37. streptococci • Diagnostic laboratory tests; • Specimen throat, pus, blood, urine, CSF • Microscopy gram +ve cocci • Culture nutrient agar, blood agar.macConkeys medium • Schultz charlton reaction this is used to detect erythrogenic toxin. • Serologic test • Group A streptococcal antigen from throat swab can be detected by commercial kits that use enzymes linked immunosorbent assay ELISA or agglutination. • Bacitracin sensitivity test commercially available discs containing a calibrate amount of bacitracin will inhibit the growth of group A streptococci but not other group of streptococci b/c group A streptococci is more sensitive to antibiotic bacitracin.
- 38. streptococci • Prevention • No specific vaccine • Rhemumatic fever can be prevented by treating group A streptococcal pharyngitis with pencillin.
- 39. streptococci • Immunity • Type specific immunity to reinfection with streptococci develops. It is due to anti M type specific antibodies. • Treatment • Penicillin G • Erythromycin • amminoglcosides