Use of modified Rambach agar to differentiate Streptococcus uberis from other mastitis streptococci

The medium of Rambach was modified to permit differentiation of mastitis streptococci. A total of 377 streptococci isolated from bovine IMI was used in the study. Of the 159 strains identified as Streptococcus uberis, 151 strains (94.9%) were beta-galactosidase-positive and yielded blue colonies on modified Rambach agar. In comparison, Streptococcus agalactiae, Streptococcus dysgalactiae, Enterococcus saccharolyticus, or Enterococcus faecalis strains were negative for propylene glycol utilization (red colonies) or beta-galactosidase production; all strains yielded colorless colonies on modified Rambach agar. However, 5 of 35 (14.3%) Streptococcus equinus strains were also positive for beta-galactosidase. Results indicate that modified Rambach agar is a convenient medium for the differentiation of the Strep. uberis from the other mastitis streptococci. Furthermore, modified Rambach agar could be easily incorporated as a screening medium for Strep. uberis in mastitis bacteriology laboratories.