A device for differentially enumerating colonies of coliform and Escherichia coli microorganisms, the device comprising: a water-impermeable first sheet; a water-impermeable second sheet attached to the first sheet; a dry, rehydratable culture medium adhered to the first sheet; wherein the culture medium comprises: organonitrogenous nutrients that facilitate growth of coliform microorganisms; a lactose-fermentation indicator system disposed in the microbial growth zone, the lactose-fermentation indicator system comprising D-lactose, a first inducer compound that enhances production of β-galactosidase, and a pH indicator; a β-D-glucuronidase indicator system disposed in the growth zone, the β-D-glucuronidase indicator system comprising 5-bromo-4-chloro-3-indolyl-β-D-glucuronide and a plurality of compounds that enhance β-glucuronidase enzyme activity in E. coli; a redox indicator; an effective amount of at least one agent that selectively inhibits growth of non-coliform microorganisms; and a first cold-water soluble gelling agent; a microbial growth zone disposed between the first sheet and the second sheet, wherein an area of the culture medium adhered to the first sheet defines the growth zone; and a second cold-water-soluble gelling agent adhered to the second sheet; wherein the first sheet is attached to the second sheet so that the culture medium is facing the second cold-water-soluble gelling agent. a water-impermeable first sheet; a water-impermeable second sheet attached to the first sheet; a dry, rehydratable culture medium adhered to the first sheet; wherein the culture medium comprises: organonitrogenous nutrients that facilitate growth of coliform microorganisms; a lactose-fermentation indicator system disposed in the microbial growth zone, the lactose-fermentation indicator system comprising D-lactose, a first inducer compound that enhances production of β-galactosidase, and a pH indicator; a β-D-glucuronidase indicator system disposed in the growth zone, the β-D-glucuronidase indicator system comprising 5-bromo-4-chloro-3-indolyl-β-D-glucuronide and a plurality of compounds that enhance β-glucuronidase enzyme activity in E. coli; a redox indicator; an effective amount of at least one agent that selectively inhibits growth of non-coliform microorganisms; and a first cold-water soluble gelling agent; organonitrogenous nutrients that facilitate growth of coliform microorganisms; a lactose-fermentation indicator system disposed in the microbial growth zone, the lactose-fermentation indicator system comprising D-lactose, a first inducer compound that enhances production of β-galactosidase, and a pH indicator; a β-D-glucuronidase indicator system disposed in the growth zone, the β-D-glucuronidase indicator system comprising 5-bromo-4-chloro-3-indolyl-β-D-glucuronide and a plurality of compounds that enhance β-glucuronidase enzyme activity in E. coli; a redox indicator; an effective amount of at least one agent that selectively inhibits growth of non-coliform microorganisms; and a first cold-water soluble gelling agent; a microbial growth zone disposed between the first sheet and the second sheet, wherein an area of the culture medium adhered to the first sheet defines the growth zone; and a second cold-water-soluble gelling agent adhered to the second sheet; wherein the first sheet is attached to the second sheet so that the culture medium is facing the second cold-water-soluble gelling agent.