Bacteria under Microscope

Streptococcus agalactiae
Group B streptococcus, GBS

streptococcus agalactiae   
                         microscopy, gram-positive cocci


Gram-positive cocci


Microscopic appearance:

Short chains of cocci, diplococci


Clinical significance:

  • Streptococcus agalactiae is a member of the gastrointestinal normal flora in some humans.
  • In the western world, S. agalactiae is the major cause of bacterial septicemia of the newborn, which can lead to death or long-term sequelae.
  • S. agalactiae is present in up to one-third of women of childbearing age, and 1.8 cases per 1000 live births will be affected by group B streptococcal infection.
    Text: Wikipedia

Colony morphology:

Streptococcus agalactiae identification
A Beta-hemolytic colonies of Streptococcus agalactiae (Group B streptococcus, GBS) on sheep blood agar. Cultivation 24 hours, aerobic atmosphere, 37°C.  
B Colonies of S.agalactiae surrounded by a zone of beta-hemolysis. Colonies of group B streptococci often have less pronounced zones of beta-hemolysis than do other beta-hemolytic streptococci (e.g. from Group A or C); some group B strains are nonhemolytic. Cultivation 24 hours in an aerobic atmosphere, 37°C. Sheep blood agar  
C CAMP reaction. Streptococcus agalactiae produce extracellular, diffusible protein (CAMP factor) that acts synergistically with beta-lysin produced by Staphylococcus aureus to produce a zone of enhanced lysis of sheep (or bovine) erythrocytes. Cultivated on Columbia agar with 5% defibrinated sheep blood, 24 hours in an aerobic atmosphere, 37°C.