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Infectious Diseasesmicrobiology

Streptococci - How to Diagnose Various Streptococci In Laboratory

Streptococci are round or oval shape bacteria and occur in chains. Streptococci are Gram positive cocci. 
These are catalase negative while staphylococci are catalase positive.

Catalase is an enzyme which converts hydrogen peroxide into water and oxygen.

Streptococci include following bacteria

Group A; S. pyogenes
Group B; S. Agalactiae
Group D; E. Facalis, E. Facium, S Bovis
S. pneumonia
Viridans group. S. mutan, S. anguis, S. mitis, S. gordoni. S. salivarius etc

Laboratory Diagnostic Features / How to diagnose different species of Streptococci .

Streptococci are diagnosed on the basis of hemolysis tests and Sensitivity Tests.

S. pyogenes:
                  It shows beta haemolysis. and it is bacitracin sensitive

S. agalactiae:
                 It also shows beta haemolysis but it is bacitracin resistant and it hydrolyzes Hippurate

E. faecalis:
                 It can be differentiated from other streptococci as it grows on bile esculin agar, whereas other streptococci don't. Some strains of E faecalis show beta hemolysis and some show alpha hemolysis. But these are resistant bacteria and can grow in harsh condition. These can be grown in 6.5 % NaCl.

S. Bovis:
            It also grows on esculin agar but it can't be cultured in 6.5 % NaCl.

S. pneumonia:

            It is bile soluble and its growth is inhibited by optochin. It shows alpha hemolysis

Viridans group:
            These are not bile soluble and their growth is not inhibited by optochin. it shows alpha hemolysis too.

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