Antibacterial characteristics and mechanisms of some herbal extracts and ϵ-polylysine against two spoilage bacterial

This study aimed to evaluate the antibacterial effects of ε-polylysine (ε-PL) and plant extracts of Thymus vulgaris, Zataria multiflora, and Salvia verticillata against the spoilage bacterium Pseudomonas aeruginosa and Pectobacterium carotovorum. Chemical compounds contained in the plants extracts were detected using HPLC and H NMR assays. To determine the antimicrobial effects, the minimum inhibitory concentration (MIC) was calculated. Scanning electron microscopy (SEM) was used to evaluate the mode of action of plant extracts and ε-polylysine on bacteria. Bacterial membrane electrical conductivity was also measured to investigate the effect of treatments on electrolyte leakage. Based on HPLC results, rosmarinic acid, caffeic acid, gallic acid, and chlorogenic acid were identified as major chemical ingredients of the extracts. Based on HPLC results, chlorogenic acid in the T. vulgaris, Z. multiflora, and S. verticillata extracts with the values of 3.209, 3.163, and 1.455 mg/L, respectively, was the dominant compound. Gallic acid, carvacrol, and p-cymene were detected in the H NMR assay as predominant secondary metabolites. The results of SEM revealed that plant extracts and ε-polylysine caused deformity of bacterial membranes. Minimum inhibitory concentration values for T. vulgaris, ε-polylysine, Z. multiflora, and S. verticillata were determined to be 0.78, 1.56, 6.25, and 25 mg/L; respectively. The electrical conductivity of bacterial cell membranes followed a dose-dependent trend. The highest electrical conductivity was observed in T. vulgaris treatment, followed by ε-polylysine and Z. multiflora.