In the fitting routine, the parameter Log CFU0 is kept fixed at
the average of the initial data points (Day zero). Two non-detect
data points (a sample non-detectable by XLD, and a different
sample non-detectable by BS) were assumed to have a concentra-
tion of 1667 CFU/sample (25 g), corresponding to 67 CFU/g, i.e., the
minimum deterministic quantifiable concentration using this
assay.