How to identify & confirm Streptococcus agalactiae at Lab


This streptococcus family is usually classified depending either on the lancefield grouping or hemolysis pattern. The step spp what I am going to discuss today is beta hemolytic and belong to group b. it is called as streptococcus agalactiae.They are gram positive spherical cells that occur in chains.

Streptococcus agalactiae



Streptococus agalactiae belongs to normal flora of female genital tract and Gastro intestinal tract. It can be Transmitted by mother to infant at birth due to rupture of membrane.

Clinical Manifestations:

 it can cause neonatal sepsis and meningitis, also neonatal pneumonia.  Not only that pneumonia, endocarditis, arthritis, osteomyelitis, post partum endometritis, cellulitis are some clinical manifestations in adults that can be caused by s.agalactiae.


when we consider the colony morphology .   s.agalactiae give compact, small colonies on blood agar.  Also there is 2-3 mm zone of beta haemolysis around colonies.




it Grow on MacConkey Agar and colonies are small Lactose Fermenting colonies (LF) . Remember. only group b,d streptococci and enterococci spp are grown on macconkey agar media.

As it is gram positive cocci we can do catalase test to differentiate staphylococcus spp from streptococcus spp. Streptococcus agalactiae give negative results for catalase test as it belongs to strep spp. the rest of the diagnostic tests are performed depending on the laboratory sops.



we can directly do the lancefield grouping based on the clinical suspicion. Lancefield grouping of isolated beta hemolytic colonies results group B Streptococci for s.agalactiae.

Streptococcus agalactiae identifacation
Streptococcus agalactiae

There are few other tests to detect s.agalactiae in clinical laboratory .

1. bacitracin disk(0.04IU) test –

This usually bacitracin disk test gives , Negative or resistant for strep agalactiae . but 5 -10% of group B,C,G streptococci also can give a positivity in Bacitracin disk test


2. CAMP test:



Stretococcus agalactiae give positive results for CAMP Test.  S. agalactiae produces a factor called CAMP factor which enhances the effect of β-lysin produced by Staphylococcus aureus. this phenomenon is used in CAMP test.

3. Hippurate hydrolysis test

it gives positive for  s.agalactie.

some sugar fermentation results can also be used. But these are the commonly performed laboratory tests for identification of s.agalactiae.

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