Evaluation of Two Fluorogenic Assays for Identification of Streptococcus Species Isolated from Bovine Mammary Glands

¹ Department of Animal Science, Institute of Agriculture, University of Tennessee, Knoxville 37901-1071

Liquid and agar assays that utilized 4-methylumbelliferyl-conjugated ß-D-glucuronide, ß-D-galactoside, or Nacetyl-ß-D-glucosaminide, and agglutination by Dolichos biflorus lectin were evaluated for identification of Streptococcus species isolated from bovine mammary glands. A greater number of Streptococcus uberis isolates were negative for N-acetyl-ß-D-glucosaminidase by the liquid assay compared with the agar assay. Enzyme profiles for Streptococcus dysgalactiae were similar by both assays. Streptococcus dysgalactiae was the only species that agglutinated when mixed with lectin from D. biflorus. Most Streptococcus agalactiae isolates were positive for ß-D-glucuronidase and ß-D-galactosidase by both assays. Two Streptococcus equinus strains had negative enzyme profiles by the liquid assay; however, both strains had enzyme profiles consistent for S. equinus by the agar method. Incorporation of 4-methylumbelliferyl-conjugated substrates into trypticase soy agar did not appear to alter agar characteristics and eliminated aliquoting substrates and inoculating tubes. More than one enzyme profile was produced per Streptococcus species or serogroup by both methods. However, some profiles were similar between species, which hindered accurate identification of Streptococcus species.

Key Words: streptococci • bovine • identification

Submitted on July 13, 1990
Accepted on September 17, 1990

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