Eirini Maniki 1, Dimitra Kostoglou 1, Nikolaos Paterakis 2, Alexandros Papachristoforou 3 and Efstathios Giaouris 1,*
1 Laboratory of Food Microbiology and Hygiene, Department of Food Science and Nutrition, School of the Environment, University of the Aegean, 81400 Myrina, Lemnos, Greece;
2 Aegean Organics, Organic Herbs and Essential Oils, 81400 Agios Dimitrios, Lemnos, Greece.
3 Department of Food Science and Technology, School of Agriculture, Aristotle University of Thessaloniki, 57001 Thermi, Thessaloniki, Greece;
* Correspondence: stagiaouris@aegean.gr; Tel.: +30 22540 83115
The growing antimicrobial resistance of many pathogenic microorganisms to the known antimicrobial agents, together with the rising environmental sustainability issues, have shifted the search for new antimicrobials to those derived from natural sources (e.g., plants). Thyme is a well-known aromatic plant that belongs to the Lamiaceae family, while its essential oil (EO) has been extensively studied for its bioactivities which are attributed to its rich content in secondary metabolites, especially terpenoids such as thymol and carvacrol. In this study, EO from a species of thyme plants (Thymus capitatus) organically cultured in Lemnos Island (north-eastern Greece) was analyzed for its chemical composition, through gas chromatography – mass spectrometry (GC-MS) analysis, antioxidant activity (AA) and total phenolic content (TPC), through the 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging activity and the Folin–Ciocalteu assays, respectively, as well as its antimicrobial and antibiofilm actions against three important foodborne pathogenic bacterial species (i.e. Salmonella enterica ser. Typhimurium, Listeria monocytogenes and Yersinia enterocolitica). For the latter investigations, the minimum inhibitory concentrations (MICs) and minimum biofilm inhibitory concentrations (MBICs) of the EO against the planktonic and biofilm growth, respectively, of each pathogen were determined, together with the minimum biofilm eradication concentrations (MBECs). To calculate the MICs, the broth microdilution method was used, while before the calculation of MBICs, the optimal conditions for biofilm formation by each target pathogen were determined using 96-well polystyrene microplates as the growth substrata. Results revealed that thyme EO was very rich in thymol, this presented very high AA and TPC, while its MICs and MBICs ranged from 0.031% to 0.063% (v/v) and 0.031% to 0.125% (v/v), respectively, depending on the target pathogen. The EO was able to fully destroy already performed pathogenic biofilms in very low concentrations. Overall, the results demonstrate that the EO of an endemic organic plant of a Greek island presents strong both antioxidant and antibiofilm propertes and could be thus further exploited as a functional and antimicrobial natural formulation for food and health applications.
