Emerging mutant populations of Listeria monocytogenes EGD-e under selective pressure of Thymbra capitata essential oil question its use in food preservation

Due to their excellent antimicrobial properties, essential oils (EO) have been proposed as potential preservatives for certain kinds of foods, such dairy products. However, the occurrence pathogenic populations that are resistant EOs could pose a health risk. This report seeks assess emergence in Listeria monocytogenes EGD-e growth at 37 °C under selective pressure Thymbra capitata EO (TCO), characterise resistance laboratory media, and identify genotypic changes, well evaluate skimmed milk. TCO cyclic treatment allowed isolation two L. strains against EO: LmSTCO by sublethal doses (75 µL/L TCO) LmLTCO lethal (300 after 20 30 cycles, respectively. Both displayed an increase minimum inhibitory bactericidal concentration higher survival rate treatments than wild-type strain (LmWT). Growth kinetics revealed better adaptation presence TCO, while grew more slowly compared LmWT, even absence antimicrobial. Moreover, slight cross-resistance antibiotics was observed: β-lactams series broad-spectrum antibiotics. The genomic study one sole nucleotide change located plsC gene codifying enzyme involved production phosphatidic acid, precursor cell membrane synthesis. Five genetic variations were found LmLTCO: among them, deletion ATP-synthesis system slowing bacterial growth. Inhibition inactivation assays milk confirmed increased both strains, thereby indicating safety risk case these emerge food chain. These results strongly suggest resistances should be taken into account order ensure efficacy natural antimicrobials design preservation strategies.