Evidence on the induction of viable but non-culturable state in Listeria monocytogenes by Origanum vulgare L. and Rosmarinus officinalis L. essential oils in a meat-based broth

摘要

Induction of viable but non-culturable (VBNC) state in Listeria monocytogenes by Origanum vulgare L. (OVEO) and Rosmarinus officinalis L. essential oils (ROEO) in a meat-based broth and phosphate-buffered saline was investigated. Occurrence of culturability loss on brain-heart infusion agar in L. monocytogenes cells (approximately 7 log CFU/mL) exposed to OVEO (5 and 2.5 mu L/mL) or ROEO (10 and 5 mu L/mL) individually in meat broth and phosphate-buffered saline, and their ability to restore culturability during a recovery treatment in phosphate-buffered saline + glucose (6 or 24 h, 30 degrees C) was evaluated. Viability of cells exposed to OVEO and ROEO was investigated with measurements of damage on integrity and membrane potential and enzymatic, efflux pump and respiratory activities. L. monocytogenes lost culturability after a 60 or 180 min-exposure to OVEO (5 and 2.5 mu L/mL) or ROEO (10 and 5 mu L/mL) in phosphate-buffered saline and meat broth. Cells exposed to ROEO in meat broth (5 and 10 mu L/mL) and phosphate-buffered saline (5 mu L/mL) restored culturability after 24 h of recovery treatment. Cells with lost culturability had variable subpopulation sizes (10.8-98.5%) with damage on measured physiological functions. Cells with lost culturability induced by OVEO or ROEO had improvements in physiological functions during recovery treatment, being indicative of viability. These results indicate that OVEO and ROEO could cause VBNC state in L. monocytogenes.