ENZYME CHARACTERISTICS OF BETA-D-GALACTOSIDASE-POSITIVE AND BETA-D-GLUCURONIDASE-POSITIVE BACTERIA AND THEIR INTERFERENCE IN RAPID METHODS FOR DETECTION OF WATERBORNE COLIFORMS AND ESCHERICHIA-COLI

Bacteria which were beta-D-galactosidase and beta-D-glucuronidase posi tive or expressed only one of these enzymes were isolated from environ mental water samples. The enzymatic activity of these bacteria was mea sured in 25-min assays by using the fluorogenic substrates 4-methylumb elliferyl-beta-D-galactoside and 4-methylumbelliferyl-beta-D-glucuroni de. The enzyme activity, enzyme induction, and enzyme temperature char acteristics of target and nontarget bacteria in assays aimed at detect ing coliform bacteria and Escherichia coli were investigated. The pote ntial interference of false-positive bacteria was evaluated. Several o f the beta-D-galactosidase-positive nontarget bacteria but none of the beta-D-glucuronidase-positive nontarget bacteria contained unstable e nzyme at 44.5 degrees C. The activity of target bacteria was highly in ducible. Nontarget bacteria were induced much less or were not induced by the inducers used. The results revealed large variations in the en zyme levels of different beta-D-galactosidase- and beta-D-glucuronidas e-positive bacteria. The induced and noninduced beta-D-glucuronidase a ctivities of Bacillus spp. and Aerococcus viridans were approximately the same as the activities of induced E. coli. Except for some isolate s identified as Aeromonas spp., all of the induced and noninduced beta -D-galactosidase-positive, noncoliform isolates exhibited at least 2 l og units less mean beta-D-galactosidase activity than induced E. coli. The noncoliform bacteria must be present in correspondingly higher co ncentrations than those of target bacteria to interfere in the rapid a ssay for detection of coliform bacteria.