SIMULTANEOUS ENUMERATION OF E. COLI AND TOTAL COLIFORMS

摘要

The general method involves contacting a bacterial colony with a β-D-galactosidase substrate and a carbon source (e.g. adonitol, esculin, salicin, amygdalin, cellobiose, etc.) metabolizable by a plurality of coliform species but not metabolizable by E. coli, and detecting reaction product signals of the substrate and carbon source. The absence of both reaction product signals indicates the presence of non-coliform bacteria; the presence of both reaction product signals indicates the presence of non-E. coli coliform bacteria; and the presence of the β-D-galactosidase substrate reaction product signal and absence of the carbon source reaction product signal indicates the presence of E. coli. A signal may identify a reaction product per se (e.g. a colored product derived from a chromogenic form of the substrate or from a chromogenic reagent which interacts with the product, etc.), or an effect of a reaction product on or at the colony (e.g. catabolite repression, growth, localized pH change, etc.). In a preferred embodiment, the β-D-galactosidase substrate reaction product signal is provided directly by a β-D-galactosidase reaction product and the carbon source reaction product signal is provided by carbon source reaction product-induced catabolite repression of the β-D-galactosidase substrate reaction product signal at a portion of the colony.