STREPTOCOCCUS SPECIES

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STREPTOCOCCUS 





 Define (Streptococcus species)
This is a Gram positive cocci occurring in chains or pair
List the species of staphylococcus 
  • Streptococcus pyogenes(Group A)
  • Streptococcus pneumoniae(pneumococci)
  • Streptococcus agalactiae(Group B)
  • Streptococcus viridans
  • Streptococcus feacalis(Enterococci)(Group D)
  • Streptococcus mitis
  • Streptococcus mutans
  • Streptococcus sangius

 Mention the species of medical importance
—  Streptococcus pyogenes
—  Streptococcus pneumoniae
—  Streptococcus agalactiae

Describe the normal habitat Streptococcus pyogenes
Streptococcus   pyogenes
—  Vegetation
—  Milk and milk production
—  Water
—  commensal are found in the upper respiratory tract.

 Describe the morphology Streptococcus pyogenes 
They are Gram positive cocci.
  • They occur in chains.
  • Are non motile.
  • Some strains are capsulated.

 Describe the mode of transmission and pathogenicity Streptococcus pyogenes 
Streptococcus pyogenes is transmitted :-
  • Inhalation-Air borne contamination arising from dressing,wound dressing,bed making,talking directly on wound
  • Transferable to clean wound from other patients with septic lesion by contamination of hands,clothing or instruments,
PATHOGENICITY
Streptococcus pyogenes causes:-
Acute sore throat(tonsilitis).
—  Scarlet fever.
—  Ear infections(otitis media).
—  Skin infections.
—  Septicemia.
—  Acute glomerulonephritis.
—  Rheumatic fever(heart valve damage).
 Enzymes and Toxins produced by Streptococcus pyogenes 
Enzymes
The above pathogenicity is due to production/secretion of enzymes and toxins
These enzymes enable the bacteria to attack an individual and cause a disease or an infection. They include:-
  • Streptokinase.
  • Hyaluronidase

TOXINS
—  Streptolysin  ”O” toxin.
—  Streptolysin “S”toxin.
—  Erythrogenic toxin.

 Describe the laboratory diagnosis for Streptococcus pyogenes
1.SPECIMENS
  • Throat.
  • Pus swab.
  • Serous fluid -depending on site of infection.
  • Blood for culture.
2.CULTURE
—  Streptococcus pyogenes produces Beta-Haemolytic colonies (colonies are surrounded by a clear zone of complete haemolysis) on BA.
—  The media used are;-
                                                              i.      Blood Agar
                                                            ii.      Macconkey Agar.

i)BLOOD AGAR AND CHOCOLATE AGAR
—  Small colonies 1-2mm white un color are produced.
—  They show Beta-Haemolysis.
.
(ii)MACCONKEY AGAR
—  Streptococcus pyogenes doesn’t grow on Macconkey   Agar.
—  NB:Crystal violet Blood Agar (CVBA)is a selective media for isolation of Streptococcus pyogenes only.

3.BIOCHEMICAL TESTS
Streptococcus pyogenes is identified using the following tests:-
—  Catalase positive
—  Bacitracin (sensitive)positive
Key Points 
Define Streptococcus
This is a Gram positive cocci occurring in chains or pair
List the species of Streptococcus
  • Streptococcus pyogenes(Group A)
  • Streptococcus pneumoniae(pneumococci)
  • Streptococcus agalactiae(Group B)
  • Streptococcus viridans
  • Streptococcus feacalis(Enterococci)(Group D)
  • Streptococcus mitis
  • Streptococcus mutans
  • Streptococcus sangius

Describe the mode of transmission and pathogenicity 
Streptococcus pyogenes is transmitted :-
  • Inhalation-Air borne contamination arising from dressing,wound dressing,bed making,talking directly on wound
  • Transferable to clean wound from other patients with septic lesion by contamination of hands,clothing or instruments,

Describe the morphology Streptococcus pyogenes
  • They occur in chains.
  • Are non motile.
  • Some strains are capsulated.

BIOCHEMICAL TESTS
Streptococcus pyogenes  is identified using the following tests:-
—  Catalase positive
—  Bacitracin (sensitive)positive
.
Evaluation 
·         List 3 media used to isolate bacteria
·         Mention 5 diseases that are caused by S.pyogenes

 

 

Streptococcus pneumoniae (pneumococci)

 

Describe the normal habitat Streptococcus pneumoniae 
NORMAL HABITAT
S. pneumoniae is part of the normal upper respiratory tract flora but as with many natural flora, it can become pathogenic under the right conditions (e.g., if the immune system of the host is suppressed).
Persons at higher risk for infection are the elderly, children under 2 years old and persons with underlying medical conditions including HIV infection and sickle-cell disease.

 

 Describe the morphology Streptococcus pneumoniae 
MORPHOLOGY
  • Streptococcus pneumoniae, or pneumococcus,
  • Gram-positive diplocci
  • Are  lancet shaped
  • Alpha-hemolytic,
  • Occurs in short chains following culture.
  • Non motile
  • Most strains are capsulated following culture

Describe the mode of transmission and pathogenicity Streptococcus pneumoniae 
Streptococcus is pneumoniae transmitted :-
By inhalation of air droplets that have the bacteria
PATHOGENICITY
Streptococcus pneumoniae causes:-
  • lobar pneumonia ,Bronchitis,menengitis,
  • Bacteremia,Otitit media,Sinusitis and conjuctivitis.
  • These infections affects the elderly and the young due to low immunity.
  • Those infected by HIV have a greater risk of infection.
 Enzymes and Toxins produced by Streptococcus pneumoniae
Enzymes
  • The above pathogenicity is due to production/secretion of enzymes and toxins
  • These enzymes enable the bacteria to attack an individual and cause a disease or an infection. They include:- Hyaluronidase
Toxin
  • Leukocidin
  • Haemolysin

 Describe the laboratory diagnosis for Streptococcus pneumoniae  
1.SPECIMENS
Depends on site of infection. They are:-
  • Sputum
  • Exudates
  • Blood-for culture
  • CSF
2.CULTURE
  • A facultative anaerobes
  • The organism is alpha haemolytic in 5-10%co2 in BA and Chocolate heated blood agar.
  • It grows on:-   
    • Blood agar
    • Chocolate blood agar.

i) BLOOD AGAR
  • Colonies appear translucent
  • They are 1-2mm in diameter.
  • Colonies are Alpha haemolytic(colonies are surrounded by an area of partial haemolysis with green- brown color. Alpha haemolysis occurs after over night incubation in co2.
  • Colonies also show ‘draughtsman shape’.
  • NB:Pneumococci shows beta haemolysis after being cultured aerobically.
ii)CHOCOLATE BLOOD AGAR
•      Colonies grow well in this media when if grown in environment enriched with co2 especially in candle jar.
3.OCHEMICAL TESTS
Streptococcus pneumoniae is:
·         Catalase negative
·         Bile solubility test positive
·         Optochin test sensitive(+ve)
NB:Bile solubility is a test used to differentiate S.pneumoniae from other streptococci species.


Key Points 
Describe the morphology Streptococcus pneumoniae
MORPHOLOGY
  • Streptococcus pneumoniae, or pneumococcus,
  • Gram-positive diplocci
  • Are  lancet shaped
  • Alpha-hemolytic,
  • Occurs in short chains following culture.
  • Non motile
  • Most strains are capsulated following culture
Describe the laboratory diagnosis for Streptococcus pneumoniae  
SPECIMENS
Depends on site of infection. They are:-
  • Sputum
  • Exudates
  • Blood-for culture
  • CSF

BIOCHEMICAL TESTS
Streptococcus pneumoniae is:
·         Catalase negative
·         Bile solubility test positive
·         Optochin test sensitive(+ve)
PATHOGENICITY
Streptococcus pneumoniae causes:-
  • lobar pneumonia ,Bronchitis,menengitis,
  • Bacteremia,Otitit media,Sinusitis and conjuctivitis.
  • These infections affects the elderly and the young due to low immunity.
Those infected by HIV have a greater risk of infection

Evaluation·      
   List 2 media used to isolate bacteria
·  Mention 5 diseases that are caused by Streptococcus pneumoniae

 




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