The appropriate growth medium (2.7 ml) was dispensed in a
5 ml sterile glass test tube that fitted within the R.A.B.I.T. cell. The
media were inoculated with 300 ml from a serial dilution of an
overnight culture, placed within the R.A.B.I.T. cell and loaded into
the incubator panel at 30 C. The change in conductance of the
detection mediumwas recorded every 6 min over a 48e72 h period
and a detection criterion of 11 mS was chosen. This value sets the
minimum difference between three successive conductance
measurements for the R.A.B.I.T. growth detection software to
calculate the time to detection (TTD) in minutes. Regression curves
were calculated using standard Microsoft Excel software to determine
correlation between TTD and inoculum (CFU/ml). The slope of
inoculum concentration plotted against TTD was also calculated
using standard Microsoft Excel regression analysis software and
reflects the relative rate to detection (RRTD). This RRTD value has
been previously used as a measure of specific growth rate (h1)
(Cuppers and Smelt, 1993), and was calculated from 1/
slope ln(10) 60.