2.5. Determination of biofilm inhibition - inhibition of initial
bacteria cell attachment
The plant extracts at MIC value concentration were evaluated for
their inhibition potential against cell attachments (antiadhesion
test). 100 ml of each plant extract (at MIC value) was added to each
well of a 96-well microplate. An equal volume ciprofloxacin
(0.00125 mg/ml) (MIC value) was added as positive control, while
the negative control was containing 100 ml MHB instead of plant
extract. Finally, 100 ml of bacteria culture (106 CFU/ml) was pipetted
to each well (final volume was 200 ml in each well). 200 ml of MHB
was added in blank wells without bacteria culture. The plates were
wrapped loosely with parafilm and incubated at 37 C for 8 h
without shaking to allow the cells to attach to the surface.
Following incubation, the contents of each well were removed.
Wells were rinsed three times with sterile distilled water to remove
loosely attached cells and non-adherent cells. The plates were airdried
and oven-dried at 60 C for 45 min. This step was validated
by staining the recovered wells with crystal violet (1%). The wells
were stained with 200 ml of 1% crystal violet and incubated at room
temperature for 15 min. The plates were then rinsed three times
with sterile distilled water to remove unabsorbed stain. The wells
were destained by adding 150 ml of ethanol. 100 ml of the destaining
solution was then transferred to a new plate and the absorbance
was measured at OD590 nm using a microplate ELISA reader (Labsystems
Multiskan MS, Finland). Each assay was performed in
triplicate. The mean absorbance of the samples was determined,
the absorbance in blank well was subtracted from absorbance
reading and percentage inhibition and efficiency was determined.
The percentage inhibition was then compared with the positive
control (Sandasi et al. 2010):
Percentage inhibition ¼
ODNegative