Most strains of Group D Streptococci are now classified in the genus Enterococcus (1). These organisms are found as normal flora in the gastrointestinal tracts of humans and animals. They are becoming increasingly important agents of human disease, largely because of their resistance to antimicrobial agents to which other Streptococci are generally susceptible (2). The most common species are Enterococcus faecalis and Enterococcus faecium. These organisms grow on media with high salt content and are usually non-haemolytic, but sometimes show alpha or beta-haemolysis. It can withstand heat at 60°C for 30 minutes, a distinguishing feature from other streptococci, and also grow within a wider temperature range (10-45°C). They ferment sugars with acid production. Differential Agar for Group D Streptococci is a modification of SF Broth (Streptococcus faecalis Broth) (3).
Brain heart infusion, peptic digest of animal tissue and casein enzymic hydrolysate in the medium provide necessary nitrogenous compounds and other essential nutrients for growth. Dextrose is the energy source. Sodium chloride at 6.5% concentration makes the medium differential for Enterococcus and Streptococcus. Growth on this medium turns yellow due to acid production. A negative reaction is indicated by no change in the purple color of the medium.
Storage and Shelf-life:
Store below 30°C in tightly closed container and the prepared medium at 2 - 8°C. Use before expiry date on the label
References:
1. Collee J. G., Fraser A. G., Marmion B. P., Simmons A., (Eds.), Mackie and McCartney, Practical Medical Microbiology, 1996, 14th Edition, Churchill Livingstone
2. Koneman E. W., Allen S. D., Janda W. M., Schreckenberger P. C., Winn W. C. Jr., 1992, Colour Atlas and Textbook of Diagnostic Microbiology, 4th Ed., J. B. Lippinccott Company Philadelphia, Pg. 440.
3. Atlas R. M., 1997, Handbook of Microbiological Media, 2nd Ed., Parks L.C., (Ed.), CRC Press, New York.