Theremay be concerns that biofilm cells (attached and growing on a
surface) may have a different physiology to cells grown free floating (as
planktonic cells) in growthmedium, hence the need to validate the calibrations
based on planktonic cellswith samples of biofilm. The comparison
work between planktonic cultures and biofilm was carried out in
similar studies because there was a discrepancy between the impedance
result and that of the reference method based on planktonic cells
(Flint, Brooks, & Bremer, 1997). However, in this study, the impedance
calibration based on planktonic cells provided a good estimate of the
numbers of biofilm cells.