Rapid detection of faecal coliforms in sewage using a colorimetric assay of β- d-galactosidase

A rapid colorimetric method has been developed for the detection of faceal coliforms in sewage. The method is based on the hydrolysis of o-nitrophenyl-β- d-galactopyranoside by the bacterial enzyme β- d-galactosidase and detection of liberated o-nitrophenol. Enzyme activity correlated well with numbers of faecal coliforms determined by conventional membrane filtration over a range of bacterial concentrations. A lower limit of 10 3 faecal coliforms per ml could be detected within 60 min. It is proposed that the method, which is amenable to automation, may be used as a surrogate for monitoring faecal coliform concentrations in sewage and a variety of effluents with a view to providing an early-warning indicator of sewage contamination or leakage.