An evaluation of potential interferences in a fluorimetric assay for the rapid detection of thermotolerant coliforms in sewage

A 1-h fluorimetric assay of beta-D-galactosidase activity was evaluated for determining thermotolerant coliforms (TTC) in sewage samples. Above TTC concentrations of 2.3 x 10(3) colony-forming units (cfu) 100 ml(-1), the assay response was related to TTC concentration. However, below this concentration, a large background signal was observed which was independent of TTC concentration. A separation scheme involving various filtration treatments and additions of a beta-D-galactosidase inhibitor was devised and used to quantify the sources of this anomalous assay response. The interferences encountered were largely due to the presence in sewage of non-specific cell-free enzymes or other cell-free substances that were capable of hydrolysing the fluorogenic substrate. Despite this apparent limitation, the fluorimetric enzyme assay has potential as an 'early warning' indicator of treatment process failure and gross sewage contamination and leakage in situations where TTC concentrations exceed 2.3 x 10(3) cfu 100 ml(-1).