2.7. Antibacterial assay
In-vitro antibacterial activity tests for the different polysaccharide extracts (S1-Glu, S2-Glu, S1 –Visco, S2- Visco, S1-Gal and S2-Gal) were carried out by disc diffusion technique ( Bauer, Kirby, Sherres, & Turk, 1966) using Whatman No.1 filter paper discs with 5 mm diameter. The discs were soaked in a 100ug/mL concentration of each tested extract. Standard antibiotics were employed as positive controls, whereas sterile saline was used as a negative control. Two different bacterial strains; Escherichia coli (gram –ve) and Staphylococcus aureus (gram + ve) were cultured in petri dishes containing the tested sample, the standard antibiotic or the negative control. All petri dishes were then incubated at 37 °C for 24 h. After incubation, the zone of inhibition (expressed in mm) was measured for each of the tested samples and the standard antibiotics. The antimicrobial index was calculated according to the following relation
equation(2)
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Indices that are equal to or higher than 1.0 indicate high antimicrobial effect compared to the standard antibiotics.