The Combined Effect of Shallot Extract by Vacuum Rotary Evaporator Technique with Common Antibiotics Against Multi-Drug-Resistant Bacteria Using the Checkerboard Technique

Allium hirtifolium (Persian shallot) belongs to the Alliaceae family. Recently, the ethanolic extract of Persian shallot was shown to have significant activity against some of the important clinical pathogens. This study has been assessed the in vitro antibacterial potency of ethanolic extracts of Persian shallot (Iranian Moosir) combined with common antibiotics against five clinically important antibiotic-resistant pathogens.  Antibacterial activities determined through disk diffusion. Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were evaluated by the broth microdilution method for the extract and selected antibiotics. Finally, the checkerboard technique applied for evaluation of the combined effect of the extract and antibiotics.  The MICs of the extract and antibiotics ranged from 4 to 16 mg/mL and 4 to 128 µg/mL, respectively. The MBCs of the extract and antibiotics varied from 8 to 16 mg/mL and 8 to 128 µg/mL, respectively. The results of the checkerboard technique showed that Amikacin and Trimethoprim/sulfamethoxazole have synergistic effects, but Levofloxacin, Imipenem, and Vancomycin have antagonistic impacts in combination with the extract on all isolates.  It is suggested by the findings of this study which the in vitro application of Persian shallot extract combined with Amikacin and Trimethoprim/sulfamethoxazole. The mentioned combinations can inhibit the growth of five clinically significant antibiotic-resistant pathogens effectively.