2.7. Biofilm metabolic activity measurement
The metabolic (respiratory) activity of biofilm was determined
by using (XTT) reduction assay. Biofilm formation was done as
described above. Following incubation (24 h), the contents of each
well were removed, and wells were washed three times with
phosphate-buffered saline (PBS) to remove loosely attached cells.
The sodium salt of XTT (2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)-
2H-tetrazolium-5-carboxanilide) was dissolved in PBS to 1 mg/ml
concentration, filter-sterilized and stored at 80 C. Menadione
was dissolved in acetone to 1 mM and sterilized immediately
before each measurement. Working solution of XTT/menadione
reagent was freshly prepared before each assay in ratio of 12.5:1.
Following washing, 100 ml PBS was added to each well of a 96-well
microtitre plate. 13.5 ml of XTT/menadione mixture was then added
to each well; the plate was gently shaken, then covered (in darkness)
and incubated at 37 C for 2e3 h. Following incubation, the
absorbance was measured at 490 nm. Blank well, negative and
positive controls were performed as described above. Each assay
was performed in triplicate (Chaieb et al. 2011; Pettit et al., 2005j).