POSSIBLE INTERFERENCE OF LACTOSE-FERMENTING MARINE VIBRIOS IN COLIFORM BETA-D-GALACTOSIDASE ASSAYS

An investigation into possible interferences in beta-D-galactosidase-b ased assays for coliform bacteria in marine waters was carried out. A rapid instrumental fluorescence assay for beta-D-galactosidase activit y, using 4-methylumbelliferyl-beta-D-galactoside as a substrate, was u sed to investigate activities of this enzyme in non-coliform bacterial isolates from coastal waters. Only 2% of isolates showed slight enzym e activity after a 1-h incubation period at 44.5 degrees C. At a lower incubation temperature of 20 degrees C, 51% and 94% of the isolates s howed some enzyme activity within 6 h and 48 h, respectively. Fifty-ni ne out of 67 of these isolates were identified as Vibrio species. A la c(+) strain of Vibrio vulnificus was found to produce beta-D-galactosi dase which caused significant false-positive reactions in the Colilert -Marine Water assay when present at concentrations of 10 cfu ml(-1) or greater. This interference could be overcome by addition of the vibri ostatic agent O/129. The high fluorescence of this reagent, however, p recluded the simultaneous determination of Escherichia coli in the Col ilert test and also its use in instrumental fluorescence assays. It wa s concluded that in assays employing high temperatures and short incub ation times, Vibrio species are unlikely to cause significant interfer ences.