Cell free preparations of probiotics exerted antibacterial and antibiofilm activities against multidrug resistant E. coli

Abdelhamid, Ahmed G.; Esaam, Aliaa; Hazaa, Mahmoud M.

After the treatment periods in preceding experiments, quantification of the biomass was carried out by CV assay (Djordjevic et al., 2002) . The amount of biofilm formed on wells surface is reflected by the amount of stain absorbed. After incubation, the culture medium was discarded from each well and then all wells were washed three times with sterile distilled water to remove any loosely adhered cells. The microtitre plate was allowed to be airdried, then further dried in the oven at 60°C for 35 min and finally stained with 150 ml of 0.1% crystal violet. After incubating the microtitre at room temperature for 20 min, the wells were washed two times with sterile distilled water to remove the excessive unabsorbed stain. For estimating biofilm density, the absorbance was determined at 595 nm using an automated microplate reader (Sun Rise -TECAN. Inc. Ò USA). The mean absorbance (OD 595 nm ) of test organisms was determined and the percentage inhibition was calculated using the following formula (Eq. (1)):