FALSE-POSITIVE FLUORESCENCE BY PINK SALMON TISSUE AND STAPHYLOCOCCI IN A RAPID TEST FOR ESCHERICHIA-COLI

Fluorescence from 4-methylumbelliferyl-beta-D-glucuronide (MUG) hydrol ysis is a common, rapid method for determining Escherichia coli in wat er and food. False-positive fluorescence occurred when either pink sal mon fillets were tested or beta-glucuronidase-positive Staphylococcus species were present in other fish products. Salmon fillet, E. coli, S . xylosus, and S. warneri produced 2, 17, 39, and 43 nmol of 4-methylu mbelliferone per mi, respectively, in a one-step detection broth (laur yl salts tryptose broth with MUG) for E, coli after 48 h at 35 degrees C. These false-positive reactions need to be considered when testing fish products, especially those contaminated through human handling.