Streptococcus

INTRODUCTION:

• Gram +ve cocci
• Arrangement in chains or pairs 
• Phylum Firmicutes and the order Lactobacillales (lactic acid bacteria). 
• Most are oxidase-negative and catalase-negative, and many are facultative anaerobes.
• Cell division along a single axis in these bacteria

Brown’s classification:

1.α- hemolitic( green)

1. Streptococcus pneumoniae( optochin sensitive, bile soluble, capsule=>quellung+)
2. Streptococcus  viridans(mutans,sanguis optochin resistant,no capsule, bile insoluble)

2.β- hemolitic(clear)

1. Streptococcus pyogens( group A, bacitracin sensitive)
2. Streptococcus agalactiae( group B, bacitracin resistant)

3.  γ-hemolitic: Entrococcus

1. E. faecalis
2. E. faecium

Lancefield grouping:

• Hemolysis on agar plates containing sheep blood:
• Lancefield classification is based on carbohydrate ‘C’ antigen
• Group A – S.pyogenes
• Group B – S. agalactiae
• Group C – S.equisimilis, S. equi, S.zooepidemicus, S.dysgalactiae
• Group D -E. faecalis, E.faecium, Enterococcus durans and S. bovis(most heat resistant >60)
• Group E – Enterococci
• Group F, G & L – S. anginosus
• Group H – S.sanguis
• Group K – S. salivarius
• Group L – S.dysgalactiae
• Group M & O – S. mitior
• Group N – Lactococcus lactis
• Group R & S – S. suis

Other Streptococcus species are classified as ‘non-Lancefield Streptococci’

 CAPSULE

• Mucoid colonies are due to production of capsule of hyaluronic acid.
• It has an antiphagocytic effect.

VIRULENCE FACTOR

M. protein

• Major virulence factor
• Responsible for resisting phagocytosis
• Resistance to infection by streptococcus is acquired as a result of antibodies to the M. Protein.

 Streptolysin O

1. Oxygen and heat labile
2.  Antigenic, causes hemolysis 
3. Acitve in reduced form
4.  ASO titres used in retrospective diagnosis Rheumatic fever (ASO titres > 200 significant)
5.  ASO titres – low after skin infection

Streptolysin S

1.  Oxygen stable, soluble in serum
2.  Not antigenic

 Pyrogenic exotoxin/Erythrogenic/Dick/Scarlational toxin – Superantigen

1.  Associated with streptococcal toxic shock syndrome Et scarlet fever
2. Pyrogenic toxin A is plasmid mediated
3.  Dick test – intradermal test to identify children susceptible to scarlet fever
4.  Schultz-Charlton reaction – diagnostic test for scarlet fever

 Streptokinase(Fibrinolysin)

• Facilitates spread of infection
• Streptokinase is produced from serotype A,C,K
• Used in retrospective diagnosis

 DNAase or Streptodornase

• Streptodornase cleaves DNA
•  Liquefies thick pus and responsible for thin serous character of streptococcal exudates Anti-DNAse,
• Anti-hyaluronidase: retrospective diagnosis of pyoderma & glomerulonephritis

 Hyaluranidase – Spreading factor 

SPECIES OF STREPTOCOCCUS & ASSOCIATED DISEASE:

• Besides Str. pyogenes, streptococci belonging to group B, C, D, F, G and rarely H, K, 0 and R may also cause human infections.
• Streptococcus causes destruction of skin grafts 

   Group B streptococci

• Human infection is caused by Str. agalactiae.
• Leaves in female genital tract
• They produce f3 – hemolysis.
• They hydrolyse hippurate.
• They may be identified by CAMP reaction.
• It is the single most common cause of neonatal meningitis.
•  Newborn infection is acquired from the mother’s vagina during birth
• Presents as septicemia, meningitis or pneumonia. 
• Late onset (between 20  & 12th weeks of life)
• Infection is obtained from the environment
• Most cases are associated with type III capsular strain
• Penicillin `G’ is the DOC.
• In penicillin allergic patients, Vancomycin is the DOC.

  Group C streptococci

• Human pathogen is strep. equisimilis
• They produce f3 – hemolysis.
• They are part of the normal flora of throat
• Can cause upper respiratory tract infection, endocarditis, osteomyelitis, brain abscess, pneumonia and puerperal sepsis.
• Ferment trehalose & ribose (Str. pyogenes ferment treholose but not ribose).
• It produces streptolysin 0 and streptokinase. Str. equisimilis is the source of streptokinase used for thrombolytic therapy.
• Penicillin G is the drug of choice for treatment.

  Group F streptococci

• Also called as ‘minute streptococci’
• Human pathogen is Str. M.G.
• Cause primaly atypical pneumonia. 

Serum opacity factor

• Some M types of streptococcus pyogenes produce a lipoproteinase which results in opacity when applied to agar gel.

DIFFERENTIAL DIAGNOSTIC TEST

• Catalase test is used to differentiate staphylococci from streptococci.
• Pneumococcus can be differentiated from streptococcus by Bile solubility test

Gram +ve cocci,arrangement in chains or pairs

 Brown’s classification:

1.α- hemolitic( green)

1. Streptococcus pneumoniae( optochin sensitive, bile soluble, capsule=>quellung+)
2. Streptococcus  viridans(mutans,sanguis optochin resistant,no capsule, bile insoluble)

2.β- hemolitic(clear)

1. Streptococcus pyogens( group A, bacitracin sensitive)
2. Streptococcus agalactiae( group B, bacitracin resistant)

3.  γ-hemolitic: Entrococcus

1. E. faecalis
2. E. faecium

Lancefield grouping

• Group A – S. pyogenes
• Group B – S. agalactiae
• Group C – S. equisimilis, S. equi, S. zooepidemicus, S. dysgalactiae
• Group D –E. faecalis, E. faecium, E. durans and S. bovis(most heat resistant > 60)
• Group E – Enterococci
• Group F, G & L – S. anginosus
• Group H – S. sanguis
• Group K – S. salivarius
• Group L – S. dysgalactiae
• Group M & O – S. mitior
• Group N – L. lactis
• Group R & S – S. suis

Other Streptococcus species are classified as ‘non-Lancefield Streptococci’

• Besides Str. pyogenes, streptococci belonging to group B, C, D, F, G and rarely H, K, 0 and R may also cause human infections.
• Streptococcus causes destruction of skin grafts  
• Group B streptococci
• Str. agalactiae.
• Lives in female genital tract
• CAMP +ve
• It is the single most common cause of neonatal meningitis.
• Newborn infection acquired from mother’s vagina during birth

DIFFERENTIAL DIAGNOSTIC TEST

• Catalase test is used to differentiate staphylococci from streptococci.
• Pneumococcus can be differentiated from streptococcus by Bile solubility test