For the CV assay (Merritt
et al., 2005), themediumwas carefully removedwith the aid of amicropipette
and the biofilms were washed three times by adding 225 μl of
phosphate buffered saline (PBS, NaCl 8 g/L; KCl 0.2 g/l; Na2HPO4
1.44 g/l; KH2PO4 0.24 g/l; pH 7.4 (Merck)) to remove unattached cells.
The resulting biofilm was stained for 30 min with 200 μl of 0.1% (w/v)
of CV (Merck), and excess of CV was removed by washing three times
with 225 μl PBS as described above. The dye attached to the biofilm
was solubilized in 70% ethanol for 30 min and the optical density (OD)
was measured at 595 nm (SpectraMax, Molecular Devices). When OD
values exceeded 1, samples were diluted in 70% ethanol and resulting
OD measurements were corrected for the dilution factor and by
subtracting the average of the blank. The resulting measurement was
defined as the total biofilm. Each plate was prepared in triplicate and
three independent biological replicates were analysed per condition.