PLANT AND ALGAL INTERFERENCE IN BACTERIAL BETA-D-GALACTOSIDASE AND BETA-D-GLUCURONIDASE ASSAYS

Several commonly occurring fresh water and marine plants and algae wer e screened for beta-D-galactosidase and beta-D-glucuronidase activitie s by using a 60-min enzyme assay based on the hydrolysis by these enzy mes of 4-methylumbelliferyl-beta-D-galactoside and 4-methylumbellifery l-beta-D-glucuronide, respectively. All freshwater plant extracts test ed showed beta-D-galactosidase activity several at relatively high lev els, and a number also showed beta-D-glucuronidase activity. A number of the macroalgae showed no activity of either enzyme, but those showi ng beta-D-galactosidase activity also showed beta-D-glucuronidase acti vity. The majority of microalgae showed some beta-D-galactosidase acti vity, but few showed beta-D-glucuronidase activity. Further studies, u sing the commercial Colilert test and the marine water formulation of Colilert, revealed that 2 of 11 of the microalgal species and several of the plant extracts tested caused positive reactions, It was conclud ed that several plant extracts and algae could significantly interfere with the detection of coliform bacteria and Escherichia coli with the use of rapid assays, on the basis of their production of beta-D-galac tosidase and beta-D-glucuronidase, respectively. The significance of t he plant and algal interferences in tests such as Colilert is dependen t on the levels of enzymes released under natural conditions, the dilu tion which they may undergo, and the numbers of algal cells present. T his also applies to interferences in rapid enzyme assays. The results of this study demonstrate the potential for interferences in bacterial enzyme assays of waters that contain high plant or algal biomass and suggest the need for masking agents to reduce the contribution of plan t and algal enzymes to the response of the assay for the analysis of s uch waters.