Biofilm susceptibility assay
Two selected isolates were grown in the Calgary Biofilm Device
(commercially available as the MBEC AssayTM for Physiology &
Genetics (P & G), Innovotech Inc., Edmonton, Alberta, Canada).
Table 2. MIC and MBC values (mM) of [Cnmim]Cl against
The biofilm assay was conducted according to the MBECTM assay
protocol supplied by the manufacturer [54], with slight modifications.
Inocula of each organism were prepared in LB broth as
described above and adjusted to a final density of 16107 CFU/ml,
as verified by total viable count. 150 mL of each inoculum were
transferred to each well of the 96-well microtitre plate packaged
with the MBEC assay. The plate lid containing 96 pegs was placed
into the microtitre plate and all plates were incubated in a
gyrorotary incubator at 28uC and 100 rpm for 24 h. Positive and
negative controls were included in each plate (6 replicates). After
24 h, biofilm counts (expressed as CFU/peg) were obtained
according to the manufacturer’s instructions. The peg lid of each
MBEC plate was rinsed three times a 96-well plate containing
0.9% saline and transferred to a ‘challenge’ plate, each well of
which contained 200 mL of LB broth containing the ionic liquids
to be tested, prepared by serial doubling dilutions as described
above. Positive and negative controls were included in each plate.
After 24 hours’ exposure to the challenge plate, the peg lid was
removed, rinsed three times in 0.9% saline and transferred into a
‘recovery’ plate with each well containing 200 mL LBB. All plates
were sonicated for 15 minutes to dislodge the biofilms into the
recovery media and the peg lid was discarded. Recovery plates
were incubated for 48 h and visually checked for turbidity, and an
MBEC value was assigned as the lowest IL concentration at which
no growth was observed after 48 h incubation, which was
confirmed by recording optical density measurements at 550 nm