Understanding Streptococci: Classification, Pathogenesis, and Disease

1. Streptococci By: Prof. A.M.Kambal Consultant Microbiologist & Head of the Bacteriology

2. Streptococci • Definition: Gram position cocci in chains, non sporing, non motile, some capsulated, facultatively anaerobic and fastidious in nutritional requirements.

3. Growth & Clonial Morphology • Blood agar best medium with optimum temperature of 35 - 37°C & under aerobic conditions. • Colonies after 24 hours incubation: about 0.5 – 1mm in diameter & may/may not be surrounded by haemolysis. • They are catalase negative.

4. Classification on Basis of: • Haemolysis on Blood Agar • Lancefield Grouping • Sterotyping

5. &ß Hemolysis

8. Based on Haemolysis on Blood Agar • β-haemolytic Streptococci (BHS) – complete haemolysis of the red cells around the colonies, producing clear zones around them. e.g. group A, group B etc… • -haemolytic Streptococci – partial haemolysis with greenish discoloration of the areas surrounding the colonies. e.g.Streptococcus viridans, Streptococcus pneumoniae • Non-haemolytic Streptococci e.g. Enterococcus faecalis

10. 2. Lancefield Grouping • Usually done on β-haemolytic streptococci (BHS). Based on the presence of a carbohydrate component of cell wall the C carbohydrate. About 20 Lancefield groups designated as A,B,C,D, (A-H) (K-U). • Detected by reacting extract of carbohydrate C antigen with specific antisera raised against it.

11. Lancefield Agglutination

12. b-heamolytic Streptococci S. pyogenes A S. agalactaie B S. dysgalactiae subsp. Dysgalactaie C subsp. Equismilis A,C,G,L S. equi subsp equi C subsp zooepidemicus C S. canis G S. anginosus A,C,F,G S. constellatus subsp.constellatus F subsp. Pharyngis C S. intermedius none S. procinus E,P,U,V,none S. iniae none S. phocae C,F S. didelphis none

13. 3. M Serotyping • Done on only group A streptococci and based on the M protein found in Group A Streptococci. 60 such serotypes; useful for epidemiological studies.

14. Group A Streptococci(Lancefield Grouping)(Streptococci Pyogenes) • Most common pathogen of the streptococci. • Causes 90% of Streptococcal diseases. • Distinguished from other BHS by the bacitracin test: All Group A are sensitive while the rest are resistant. • It may be capsulated and the capsule is composed of hyaluronic acid.

15. Superantigen

16. Bacitracin test

17. PYR +

18. Pathogenicity Determinants: • Extracellular Determinants: • Streptokinase: Convert plasminogen to plasmin which then lyses fibrin. Used to treat thrombotic states. e.g. Coronary thrombosis.

19. 2) DNAase: depolymerises DNA 4 main DNAases: A B C D Antibodies produced against DNAase (anti-DNAase B) is useful for diagnosing recent Group A Streptococcal infections especially skin infections.

20. 3) Erythrogenic Exotoxin • Produced only by Group A Streptococcal lysogenised by a β-bacteriophage. It is also called Streptococcal pyrogenic exotoxin (SPE).

21. 4) Streptolysin (Haemolysin) • Lyses all types of cells, not only RBC. Two Types: • Streptolysin O – Oxygen Labile • Streptolysin S – Oxygen Stable

22. Leucocidin: • Destroys WBC and platelets. • Hyaluronidase: • Degrades hyaluronic acid

23. Pathogenesis • Causes suppurative infections and non-suppurative complications (or sequalae).

24. Diagram of Cell Wall Section of Streptococcus Pyogenes

25. Suppurative (Pyogenic) Infections • Virulence Factors • Principal virulence factors is the M protein. Originated from the cytoplasmic membrane. Associated with pili. It is antiphagocytic. • Lipotechoic Acid (LTA) For attachment to epithelial surfaces. (iii) Hyaluronic Acid An antiphagocytic capsules.

26. B. Diseases • Tonsillitis/Pharyngitis: • Acute suppurative infection of the tonsils & pharynx. Prevalent in children. most common bacterial infection of throat. May spread to adjacent tissues & cause: Peritonsillar abscess (Quinsy), sinusitis, ototis. • Impetigo (Pyoderma): • An infection of the epidermis presenting as pustules. Seen most often in infants and toddlers.

27. Erysipelas: • A serious infection often complicating surgical wounds. • Cellulitis: • A spreading infection of the subcutaneous tissue. • Scarlet Fever: • This is a combination of tonsillitis & a red skin rash. • Toxin lysogenised by β-bacteriophage.

28. Puerperal Sepsis: • Acute infection of the female genital tract. • Severe Necrotising Fasciitis & Other Soft Tissues: • Severe infection usually seen in people under 50 years with no underlying disease.

29. B. Non-suppurative Complications of Group A Streptococcal Infections • These are antigen-antibody mediated disease and occur about 1-5 weeks after the primary suppurative infection. Tend to follow either throat or skin infections or both. Streptococci are not found in the affected organ.

30. a) Acute Rheumatic Fever: • Considered to be an autoimmune disease involving the myocardium and its valves, connective tissues and the big joints. • Group A Strep cell wall has some antigenic similarity with some of these human tissues. Follows after throat infections only. Tends to recur. Many serotypes are associated with acute rheumatic fever.

31. b) Acute Glomerulonephritis: • Due to antigen-antibody complexes deposited on the basal membrane of glomeruli also can be due to similarity between group A cell components and glomerular tissue. May follow after either throat or skin. Tends not to recur. Serotypes involved are few called nephrotogenic strains.

32. Differences Between Glomerulonephritis & Rheumatic Fever

33. Differences Between Glomerulonephritis & Rheumatic Fever (Continued)

34. Epidemiology of Streptococcal Infections • Acquisition is acquired through infected respiratory droplets. • Sources of Infection a)Those with active disease or convalescent carriers in throat. b)Asymptomatic carriers – the most common source. Up to 20% of school going children may carry Group A streptococci in their throats. 3. Age Group: prevalent in children especially between 3 – 8 years.

35. Diagnosis of Suppurative Infections • Specimen: • Swabs: Wounds Throat • Blood • Aspirates 2) Culture – B.A. At 37°C Aerobic; 18 – 24 Hrs, Incubation Period. • Bacitracin Test • Lancefield Grouping

36. Treatment • Penicillin : Antibiotic of choice • Other Antibiotics: Erythromycin/other macroslides Cefuroxime & the 3rd generation Cephalosporins e.g. Ceftriaxone

37. Group B Streptococci(Streptococci agalactiae) A member of the normal flora of the female genital tract and rectum. Up to about 25% pregnant women carry it.

38. Disease By Group B Streptococci • Important in Neonatal infection: • Early-onset Disease: severe disease develops within 24 – 48 hrs. after birth. Infection acquired either in-utero or during passage through birth canal. Associated with: • Premature Birth • Prolonged & early rupture of fetal membranes. • High mortality rate: 60 – 70% Disease presents as Respiratory Distress syndrome or Septicaemiaor Meningitis.

39. Late-onset Disease: Often occurs in full term neonates without any underlying disease. Infection occurs in the 2nd week of birth. Prognosis better than early onset: Mortality rate about 10%. Usually present as meningitis.

40. Treatment • Penicillin /Ampicillin • Sometimes may be combined with Gentamicin.

41. Group D Streptococci • Has 2 main subgroups: • Enterococci • Non-enterococci Both are part of the normal intestinal flora. 1) Enterococci: can grow in the presence of 40% bile & 6.5% sodium chloride. They are generally resistant to Penicillin, but sensitive to Ampicillin.

43. 2 Main Human Pathogens: • Enterococcus faecalis • Enterococcus faecium

44. Non-enterococci: • Cannot grow in the presence of 6.5% sodium chloride. Sensitive to penicillin. • Main human pathogen is Streptococcus bovis. • Group D Strep can cause urinary tract infections, endocarditis, and wound infections.

45. -Haemolytic Streptococci 2 Main Members: • Viridans streptococci and • Streptococcus pneumoniae(Pneumococcus) Viridans streptococci consists of many members e.g.: S. sanguis S. mutans S. salivarius

47. Sensitive to optochin

50. Viridans streptococci Members are predominant normal flora of the oropharyn. They are generally opportunistic pathogens.