Evaluation of antimicrobial activity of natural antimicrobials against antibiotic-sensitive and resistant phytopathogens

Crop diseases caused by phytopathogens threaten a stable food supply. Although antibiotics are widely used to prevent these diseases, their use is becoming increasingly limited owing to their toxicity. In this study, we evaluated the efficacy of natural antimicrobials against both antibiotic–sensitive (S) and antibiotic-resistant (R) phytopathogens. The results showed that grapefruit seed extract (GSE) and several carboxylic acids exhibited broad-spectrum inhibitory effects against phytopathogens, irrespective of antibiotic resistance. Among these, GSE showed the highest antimicrobial activity against all strains with a minimum inhibitory concentration (MIC) value of ≤ 0.0781%. Our findings reveal that these natural antimicrobials could serve as substitutes for chemical pesticides; however, further studies are required to enhance their antimicrobial efficacy for practical applications in agriculture.