Multidrug-resistant bacteria strains is becoming a serious problem, so new technology applied plant extract as a natural antimicrobial source combined with antibiotics to overcome this problem by using new method as the Decimal Assay for Additivity (DAA)  to define the end point for additivity as the interactions could be respectively defined as synergism or antagonism. The  present study was carried out to evaluate the antimicrobial activity of five plant extracts prepared by the ultrasonic-assisted methanol extract (UAE) as zingeber officinalis  (Ginger), camellia sinensis (Green tea), curcuma longa (Turmeric), pelargonium graveolens (Geranium) and thymus vulgaris (Thyme) combined with antibiotics like amoxicillin, doxycycline , gentamicin and difloxacin against  90 samples from  dead and diseased rabbits with (10) isolates belonging to one Gram positive field strain of Listeria monocytogen by using agar diffusion method. The mean zone of inhibition (IZ) of methanol plant extracts and antimicrobial agents determined at different concentrations, Also, the minimum inhibitory concentration (MIC) (the lowest concentration which prevent visible growth of the bacteria) was determined for the tested plant extracts and the used antibiotics and for combination between them by the twofold dilution method, as the antimicrobial activities were assessed by using disc diffusion method. Total phenolic content (TPC) of plant extracts was determined by the Folin–Ciocalteu method, also the antioxidant activity of the extract was determined by the (DPPH) assay. Results revealed synergistic effects appear in thyme with amoxicillin by ratio (6:4),(5:5) while green tea with amoxicillin by ratio (7:3),(6:4) and gentamicin by ratio (6:4)  finally turmeric with  doxycyclin by ratio (5:5) , with gentamicin with (6:4) ,while with difloxacin by ratio(6:4), (5:5)