Antibiotic resistance has become a serious health concern globally, and the discovery of plant-based antimicrobials may provide valuable and cheap solutions to overcome the problem. The combinational effects of Sanguisorba officinalis, Smilax china, Agrimonia pilosa, Cornus officinalis, Bridelia speciosa, Pulsantilla chinesis, Crytomium fortunei, and Hedyotis diffusa in combination with erythromycin and penicillin against Salmonella enterica (NCTC 13349) and E. coli (NCTC 11560 and 13352) were examined using the checkerboard method. The MIC of four of the plant infusions was 0.625 mg/mL against S. enterica and ranged between 0.078 mg/mL and 0.625 mg/mL for the two strains of E. coli. Four infusions were effective against E. coli (NCTC 11560) and five against E. coli (NCTC 13352). The MIC of erythromycin (alone) was 64 mg/L against S. enterica (NCTC 13349), and the MIC of penicillin (alone) was 128 mg/L against E. coli (NCTC 11560 and 13352). In combination, plant infusions reduced the MIC of the antibiotics up to 500 folds, resulting in 99% potency while their MIC increased up to 8 folds. S. officinalis infusion in combination with erythromycin and penicillin showed the highest combination therapy against S. enterica and the two E. coli while P. chinesis showed the highest antagonism with penicillin against E. coli (NCTC 13352). The current study showed that the potency of antibiotics was improved against the tested bacterial strains when screened in combination with plant infusions, thus supporting the drug combination strategy to combat antibacterial resistance.