Potential synergistic effect of Alhagi graecorum ethanolic extract with two conventional food preservatives against some foodborne pathogens.

The present study aims to screen the anti-bacterial activity and synergistic interaction of A. graecorum Boiss. ethanolic extract with two food preservatives against five strains of foodborne bacteria. Disk diffusion and minimum inhibitory concentration were used for anti-bacterial assay, checkerboard assay and time-kill curve were used for the combination studies. HPLC analysis and molecular docking study were performed to corroborate the in vitro results. The ethanolic extract showed anti-bacterial activity against all tested bacterial strains with inhibition zones from 7.5 to 9.3 mm and MIC values ranged between 1.2 and 1.8 mg mL. The combination of the ethanolic extract with Na-benzoate or Na-propionate resulted in synergistic and additive interactions against the tested bacteria with fractional inhibitory concentration index (FICI) ranges 0.31-0.63 and no antagonism was shown. Time-kill curve assay showed that the synergistic and additive combinations have inhibitory effects on the tested strains. The ethanolic extract combination with Na-benzoate or Na-propionate can be used for development new sources of food preservatives. Testing new different natural plant extracts with food preservatives will help develop new anti-bacterial agents.