Phenotypic and transcriptomic investigation of the antibacterial mechanism of hexahydro-colupulone against Listeria monocytogenes and its application in apple juice

L. monocytogenes is a dangerous food -borne pathogen threatening global food safety, and its antibiotic resistance is on the rise. Hop extracts and their derivatives were recently found to have antibacterial activity against L. monocytogenes, while the antimicrobial mechanism remains unclear. In this study, a new hop derivative, hexahydro-colupulone (HHCL), was prepared based on hop extracts. HHCL inhibited the growth of L. monocytogenes at surprisingly low concentrations (MIC = 0.4 mu g/mL). HHCL significantly inhibited the survival of L. monocytogenes in apple juice and decreased the total viable counts in apple juice during storage (10 days). Sensory evaluation results suggested that the addition of HHCL had no adverse effect on the quality of fresh apple juice and significantly delayed its browning more than 4 h. Integrating phenotypic and transcriptomic investigations revealed that HHCL inhibited L. monocytogenes growth and survival through multiple mechanisms including cell structural damage, intracellular component leakage, energy and respiratory metabolism limitation, protein synthesis block, DNA replication and repair systems damage. This study is the first to report the inhibitory effect of HHCL on L. monocytogenes and the first to reveal the antibacterial mechanism of HHCL at the gene level, which provides a theoretical basis for developing new antimicrobial agents and application of hop compounds in food safety.