this medium is used for selective isolation of Group B streptococci from clinical samples. Protein hydrolysate provides nitrogenous and carbonaceous compounds, long chain amino acids and other essential nutrients for the growth of Streptococci. Buffers present provides buffering to the medium. Selective agents in the medium inhibits accompanying flora. One of the substrate in the chromogenic mixture is cleaved by beta glucosidase possessed by Group B Streptococci resulting in blue coloured colonies.