Granada medium for detection and identification of group B streptococci

A new starch serum medium, Granada medium, for isolation and identification of group B streptococci (GBS) anaerobically as red colonies is described. The medium contains 3.8% Proteose Peptone no. 3 (Difco), 15% soluble starch 1252 (Merck), 10% coagulated horse serum, 15 micrograms of trimethoprim per ml, and 0.06 M phosphate buffer (pH 7.8; medium pH 7.4). This medium inhibited fecal flora and at the same time supported growth of GBS. A new pigment-enhancing effect of folate inhibitors on GBS is reported and used in the formulation of the medium. The good selective and differential properties of the Granada medium favor quicker and easier detection of GBS in heavily contaminated specimens. Since the medium is convenient to use and requires only 18 h of incubation to detect and identify GBS, it should be useful in any clinical microbiology laboratory and would assist in the early detection of GBS in clinical specimens.