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 °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

7. 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

9. 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.

10. 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.

11. 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.

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

14. 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.

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

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

17. Leucocidin: Hyaluronidase: Destroys WBC and platelets.
Degrades hyaluronic acid

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

20. Nonantigenic; limited role in pathogenicity
Structure
Composition
Comments
Capsule
Hyaluronic Acid
Nonantigenic; limited role in pathogenicity
Protein
M, R & T ANTIGENS
M is type antigen & adherence & antiphagocytic factors.
Polysaccharide
Rhamnose – galactosamine polymer
C-substance; Group A antigen.
Peptidoglycan
Glucosamine muramic acid w/cross-linked peptide chains
Cell wall backbone
Cytoplasmic Membrane
Protein-lipid
Nutrient & enzyme transport
Diagram of Cell Wall
Section of
Streptococcus Pyogenes

21. 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.

22. B. Diseases Tonsillitis/Pharyngitis: Impetigo (Pyoderma):
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.

23. Erysipelas: Cellulitis: Scarlet Fever:
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.

24. Puerperal Sepsis: Severe Necrotising Fasciitis & Other Soft Tissues:
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.

25. 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.

26. 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.

27. 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.

28. Differences Between Glomerulonephritis & Rheumatic Fever
Latent period between infection and first attack.
1 – 5 weeks
(Average 18 days)
(Average 10 days)
Preceding infection
Throat only
Throat or Skin
Pathogenesis Both Based On Immunological Reaction (Either Due to auto antibody Or due to cross reactive antigen).
Similarity between organism antigens & tissue antigens
Similarity between
Organism & tissue antigens.
Deposition of immunocomplexes in glomeruli

29. Differences Between Glomerulonephritis & Rheumatic Fever (Continued)
4. Second Attacks
Common
Rare if any
5. Prophylactic use of penicillin.
Essential
Usually NOT used.
6. Serotypes (M Types)
Any of the 60 serotypes
Limited No. of serotypes e.g. type 12, 45 etc.
7. Serum whole complement & C3
Increased
Decreased

30. 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.

31. 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

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

33. 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.

34. 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 foetal membranes.
High mortality rate: 60 – 70%
Disease presents as Respiratory Distress syndrome or
Septicaemia or Meningitis.

35. 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.

36. Treatment Penicillin /Ampicillin
Sometimes may be combined with Gentamicin.

37. 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.

38. 2 Main Human Pathogens:
Enterococcus faecalis
Enterococcus faecium

39. 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.

40. -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

41. Viridans strep.
Strep. pneumoniae
Resistant to optochin
Not lysed by bile salts
Opportunistic pathogen
Sensitive to optochin
Lysed by bile salts
(i.e. Bile soluble)
Primary pathogen

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

43. 2 Main Diseases: Dental plaques and caries.
Sub-acute bacterial endocarditis.

44. 1) Dental Plaques
This is the more common disease associated with this group. Dental plaque consists of oral bacteria + bacteria products and salivary components. S. mutans is the most pathogenic for dental plaque. It produces enzymes that break down dietary sugars to polysaccharides called glycans e.g. Glucans and fructans which maintain the integrity of the plaque and get it firmly fixed to the enamel surface.
Prevention:
Avoidance of sweets
Good oral hygiene – frequent
Tooth brushing & deflossing

45. Subcute Bacterial Endocarditis (SBE)
Serious infection of cardiac valves by
Viridans streptococci.

46. Predisposing Factors Valve must be abnormal: damage by
a. Rheumatic Fever
b. Congenital Cardiac valve Abnormality
c. Atheroesclertic valve
d. Prolapsed valve
e. Syphilic valve
Dental Extraction: leading to transient bacteraemia.

47. Pathogenesis:
Transient bacteraemia following dental extraction/ or any other manipulation. Circulating Viridans streptococci are deposited on damaged cardiac valve to cause lesions called vegetations components are:
Thrombi
Bacteria
Fibrin
WBC

48. Further destruction of valves, leading to cardiac murmurs and eventually cardiac failure.
SBE: One of the causes of pyrexia of unknown origin (P.U.O).

49. Diagnosis: Blood Culture
Treatment:
Combination of Penicillin & Streptomycin or Gentamycin.
NB:
Other organisms may be involved as well e.g. Enterococci, S. bovis, S. aureus.

50. Streptococcus pneumoniae
Gram positive diplococci with cells arranged end to end. Some may be capsulated. Capsulated strains usually are primary pathogens; non capsulated strains to be opportunistic.
Culture: growth is enhanced by 5-10% extra CO2.Colonies tend to collapse at the centre after 24 hours incubation. Capsulated strains produce smooth (S) and mucoid colonies whist noncapsulated produce dry and rough (R) colonies.

51. Antigenic Structure:
> 80 serotypes known based on variations in capsular structure.

52. Pathogenesis
Severe invasive and suppurative infections acquired by inhalation of respiratory droplets infected by capsulated strains. Organisms acquired by exogenous route.
Acute pneumonia-commonest infection and involves the alveoli: and often followed by invasion of the blood stream leading to.
Septicaemia
Meningitis
Arthritis
Infection may also be localised to the ears (otitis media), sinusitis or conjunctivities.

53. Secondary Infections:
Organisms tend to be non-capsulated and cause opportunistic infection when the host’s natural defense mechanisms of the respiratory tract are impaired.
Infections are endogenous.
Infections generally confined to the lungs only.

54. Factors Increasing Risk To Pneumococcal Infection
Splenectomy
Hyposplenism
Liver Disease
Asplenia
Hypogamma Globinaemia
Sickle Cell Disease
Alcoholism
Cigarette Smoking
Malnutrition

55. Diagnosis: BA Culture of Sputum CSF Blood Swab / Aspirate
Optochin Test
Capsular Swelling Test (Quellung Reaction) BA

56. Treatment:
Penicillin; but an increasing number of strains becoming resistant. In such situations.
3rd generation Cephalosporines e.g. Ceftriaxone with either Vancomycin or Rifampicin.

57. Vaccination:
Based on polysaccharide capsule given to those at risk of serious infection. Vaccine is multivalent containing the serotypes frequently associated with invasive disease.
Recommended for sickle cell disease patients and splenectomised patients.