Abstract: To evaluate the interaction between plants extract and antibacterial drugs then to confirm the rationale of the ethno-medicinal use of candidate plants. Methanolic extract of Trachyspermum ammi (Fruit), Senna alexandrina mill (Leaves) and Vachellia nilotica spp. nilotica (Fruit) individually and in combination with commonly used antibiotics (ampicillin, gentamycin and tetracycline) were tested by the Cup Plate method in crude for their antibacterial activity against four standard bacterial strains (Bacillus subtilis, Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa). The highest antibacterial activity was recorded in V. nilotica extracts against S. aureus (IZ = 39 mm) and the lowest antibacterial activity was recorded in T. ammi extract against P. aeruginosa (IZ = 0 mm). When the standard antibiotics were tested, the IZ ranged from 0-31 mm. The lowest (MIC) of the three plants extracts against the standard bacteria were determined, the most potent antimicrobial plant was V. nilotica (MIC<1.156-12.5 mg mL-1). In synergistic results the three extracts showed synergistic interaction in combination with the tested antibiotics which differed according to the species of bacteria. The Inhibition Zones (IZ) ranged from 0-40 mm. The highest largest IZ of 40 mm was observed against B. subtilis where a combination of V. nilotica and Tetracycline were used. The least susceptible bacteria to the plant extract and combination was S. aureus organisms and the most susceptible bacteria was B. subtilis. The synergy of T. ammi, S. alexandrina and V. nilotica showed an overall increase in the activity of standard antibiotics against standard bacteria, thus, there is a scope to develop effective combinations of such antibiotics and purified forms of these medicinal plants.