Synergistic antibacterial effects of carvacrol and ε-polylysine

Abstract

This study aimed to evaluate the antimicrobial efficacy of the combination of ɛ-polylysine (ɛ-PL) and carvacrol (Car) against foodborne pathogens, Escherichia coli and Staphylococcus aureus. The minimum inhibitory concentrations (MICs) of ɛ-PL (Car) against E. coli and S. aureus were 25 μg/mL (320 μg/mL) and 12.5 μg/mL (320 μg/mL), respectively. Checkerboard assays showed that the combination of ɛ-PL and Car exerted synergistic effects against E. coli and S. aureus with fraction inhibitory concentration index (FICI) of 0.375 and 0.5, respectively. It demonstrated that the combination of ɛ-PL and Car significantly inhibited the growth of the two strains compared to single treatment. Furthermore, the mode of action of ɛ-PL (6.25 μg/mL) or Car (80 μg/mL) in inhibiting E. coli and S. aureus was researched by assessing their changes with regard to cellular membrane integrity, membrane permeability, respiratory activity, and membrane structure. A combination of ɛ-PL and Car increased the damage to cell membranes and their permeability and led to the release of 260 nm absorbing materials, decreased respiratory-chain dehydrogenase activity compared with ɛ-PL or Car treatment alone. These results demonstrated that the combination of ɛ-PL and Car could be used as a new promising naturally sourced food preservative.

Carvacrol—A Natural Phenolic Compound with Antimicrobial Properties

“…A synergistic effect against E. coli CICC 10664 and S. aureus CICC 21600 was also found for the combination of ε-poly-L-lysine (ε-PL) with carvacrol [73]. ε-PL is a polymer consisting of a series of 25-35 L-lysine monomers that is derived from metabolites produced by fermentation by Streptomyces albus 346 [74].…”

“…The combination of ε-PL and carvacrol was synergistic against E. coli CICC 10664 and S. aureus CICC 21600, with fractional inhibitory concentration indices (FICI) of 0.375 and 0.5, respectively. Damage to cell membranes and a change in its permeability, as well as a decrease in the activity of the respiratory chain dehydrogenase, were observed [73].…”