The groundwater sample designated GLRF has been
previously described (Cheng et al. 1999). The river water
was obtained from Mull Creek in Ozaukee County,
Wisconsin, USA. Five microlitres containing 103 E. coli
O157:H7 cells were added to 45 ll of either groundwater,
river water, or pasteurized milk. Serial 10-fold dilutions
were made in double distilled water to a theoretical
concentration of 10)2 cells and each dilution was used in
DPCR analysis.