Simultaneous enumeration of E. coli and total coliforms

Abstract

The general method involves contacting a bacterial colony with a .beta.-D-galactosidase substrate and a carbon source metabolizable by a plurality of coliform species but not metabolizable by E. coli, and detecting reaction product signals of the substrate and carbon source. Typically, the carbon source is a carbohydrate, preferably adonitol, esculin, salicin, amygdalin, or cellobiose. 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 .beta.-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 itself (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.). Preferably, the .beta.-D-galactosidase substrate reaction product signal is provided directly by a .beta.-D-galactosidase reaction product and the carbon source reaction product signal is provided by carbon source reaction product-induced catabolite repression of the .beta.-D-galactosidase substrate reaction product signal at a portion of the colony.

Dependencies are inferred from the claim text.