Streptococci

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

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

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Growth Clonial Morphology

• Blood agar best medium with optimum temperature
  of 35 - 37C 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.

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Classification on Basis of

1. Haemolysis on Blood Agar
2. Lancefield Grouping
3. Sterotyping

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Based on Haemolysis on Blood Agar

1. ß-haemolytic Streptococci (BHS) complete
   haemolysis of the red cells around the colonies,
   producing clear zones around them.
   e.g. group A, group B etc
2. ?-haemolytic Streptococci partial haemolysis
   with greenish discoloration of the areas
   surrounding the colonies.
   e.g.Streptococcus viridans,
   Streptococcus pneumoniae
3. Non-haemolytic Streptococci e.g.
   Enterococcus faecalis

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2. Lancefield Grouping

• Usually done on ß-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.

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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.

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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.

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Pathogenicity Determinants

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

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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.

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3) Erythrogenic Exotoxin

• Produced only by Group A Streptococcal
  lysogenised by a ß-bacteriophage. It is also
  called Streptococcal pyrogenic exotoxin (SPE).

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4) Streptolysin (Haemolysin)

• Lyses all types of cells, not only RBC.
• Two Types
• Streptolysin O Oxygen Labile
• Streptolysin S Oxygen Stable

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

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Pathogenesis

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

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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
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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.

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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.

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• 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 ß-bacteriophage.

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• 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.

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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.

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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.

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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.

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Differences Between Glomerulonephritis
Rheumatic Fever
Rheumatic Fever Glomerulonephritis
Latent period between infection and first attack. 1 5 weeks (Average 18 days) 1 5 weeks (Average 10 days)
2. 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
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Differences Between Glomerulonephritis
Rheumatic Fever (Continued)
Rheumatic Fever Glomerulonephritis
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
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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.

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Diagnosis of Suppurative Infections

• Specimen
• Swabs Wounds
• Throat
• Blood
• Aspirates
• 2) Culture B.A. At 37C
• Aerobic 18 24 Hrs, Incubation Period.
• Bacitracin Test
• Lancefield Grouping

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Treatment

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

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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.

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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.

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• 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.

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Treatment

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

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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.

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2 Main Human Pathogens

• Enterococcus faecalis
• Enterococcus faecium

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• 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.

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?-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

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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
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Viridans streptococci

• Members are predominant normal flora of the
  oropharyn. They are generally opportunistic
  pathogens.

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2 Main Diseases

1. Dental plaques and caries.
2. Sub-acute bacterial endocarditis.

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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

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Subcute Bacterial Endocarditis (SBE)

• Serious infection of cardiac valves by
• Viridans streptococci.

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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.

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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

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• 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).

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• 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.

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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.

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Antigenic Structure

• gt 80 serotypes known based on variations in
  capsular structure.

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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.

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Secondary Infections

• Organisms tend to be non-capsulated and cause
  opportunistic infection when the hosts natural
  defense mechanisms of the respiratory tract are
  impaired.
• Infections are endogenous.
• Infections generally confined to the lungs only.

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

• Culture of Sputum
• CSF
• Blood
• Swab / Aspirate
• Optochin Test
• Capsular Swelling Test (Quellung Reaction)

BA
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Treatment

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

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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.