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The minimum inhibitory concentration (MIC) of the selected strains was determined using the broth micro dilution technique in a 96-well microtiter plate [41 (link)]. The methanolic extracts of the strains were dissolved and diluted in different concentrations (0.025, 0.05, 0.1, 0.2, 0.4, 0.8, 1.6 and 3.2 mg/ml) and were used to test the antimicrobial activity by growing them with bacterial culture in a 96-well microtiter plate. The ampicillin (1 mg/ml) amended bacterial culture was used as the positive control, and the bacterial cultures without treatment were used as the negative control. The plates were incubated at 37 °C for 36 h, and absorbance was taken at 700 nm in a UV–VIS spectrophotometer (MultiscanTM GO, Thermo Scientific, MA, USA). EC50 was expressed and calculated as previously described [21 (link)].

The antioxidant potential of a methanolic extract of strain DBT34 was determined using a free radical DPPH scavenging assay and ABTS radical cation decolorization assay.
The ability of a methanol extract of DBT34 to scavenge the DPPH free radical was determined by using the stable 2, 2-diphenyl-1-picrylhydrazyl radical (DPPH). Briefly, for the DPPH scavenging assay, 100 µL of different concentrations (10–100 µg/mL) of the methanolic extract was placed in 96-well plate and mixed with 200 µL of DPPH solution (0.1 mM). The samples were kept in the dark for 39 min after which absorbance was recorded at 517 nm using a multi-scan UV/Vis spectrophotometer ((Multiscan^TM GO, Thermo Scientific, MA, USA). [63 (link)]. Ascorbic acid was used as positive control, methanol as a negative control and extract without DPPH was used as a blank. Results were expressed as a percentage reduction of DPPH absorption compared to control. In addition, the antioxidant potential of a methanolic extract of strain DBT34 was also determined with a 96-well plate method using an ABTS radical cation scavenging assay. Ascorbic acid, methanol, and extract without ABTS were used as positive, negative, and blank controls, respectively. The ABTS radical cation decolorization activity was calculated according to the method described by Re et al. [32 (link)].

TPC in the methanolic extract of strain DBT34 was determined spectrophotometrically using the Folin–Ciocalteu (FC) reagent. Gallic acid was used to generate a standard curve in the range of 10–1000 mg/mL. A 200 µL volume of assay sample was prepared by combining 10 µL of sample extract with 90 µL FC reagent. This solution plus 100 µL of 15% of sodium carbonate were added to individual wells of 96-well plates. TPC was quantified as mg of Gallic acid equivalents (GAE) [61 (link)]. The total flavonoids content (TFC) in the methanolic extract of DBT34was determined using the aluminum colorimetric method. The standard curve of Quercetin solution in methanol was prepared with concentrations ranging from 0 to 500 µg/mL and absorbance was recorded at 420 nm with a UV-vis microplate spectrophotometer (MultiscanTM GO, Thermo Scientific, MA, USA). A total of 100 µL of sample extract (10–100 ug/mL) was mixed with 200 µL of 2% aluminum trichloride and used in the TFC assay. TFC was quantified as µg of Quercetin equivalents (QE) per mg of DW [62 (link)].

Minimum inhibitory concentration (MIC) of selected strain was determined by following broth micro dilution technique using 96-well microtiter plate (Eloff, 1998 (link)). Crude extract of the selected strain was prepared with 10% DMSO in different concentrations (100, 25, 500, and 1000 μg/ml). The bacterial pathogens were grown up to a final concentration of 1.0 × 10^-4 CFU/mL (OD = 0.402). Different concentrations of the crude extract were added in 96-well microtiter plate containing a bacterial culture as test and without bacterial culture as controls. Antibiotic (ampicillin, 0.01 μg/ml) along with bacterial cultures were used as positive control, DMSO containing bacterial cultures were used as negative control. The plates were incubated at 37°C for 36 h and absorbance was taken at 620 nm in spectrophotometer UV-VIS (MultiscanTM GO, Thermo Scientific, MA, USA). IC₅₀ was expressed as the concentration (μg/ml) of crude extract at which 50% of bacterial growth was inhibited and was calculated using the calibration curve by linear regression.

Cell viability was evaluated using the 3-(4, 5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Briefly, the cells were seeded on a 96-well plate. At the indicated time points after seeding, cell viability was determined by measuring the absorbance of MTT (Invitrogen, USA) at 490 nm using a microplate reader (MultiscanTMGO, Thermo Fisher, USA).

Cell viability was determined using the Cell Counting Kit-8 (CCK-8) kit (Beyotime, Shanghai, China) according to the protocol. Briefly, 3×10³ cells were seeded in each well of 96-well plates and were cultured overnight. According to the instructions, CCK-8 reagent was added at indicated time points and incubated at 37°C for one h. The absorbance was measured at 490 nm using a microplate reader (MultiscanTMGO, Thermo, USA).