Evaluation of Different Chemotypes of Lavandula angustifolia Essential Oils as Phytobiotics for the Control of Clinical Escherichia coli Strains Isolated from Commercial Poultry Production

The study focused on evaluating the antibacterial activity of ten essential oils (EOs) representing different origins and chemotypes of common lavender (Lavandula angustifolia), as well as their two major constituents, linalool and linalyl acetate. The aim of the study was to evaluate their potential as natural phytobiotics against clinical Escherichia coli strains isolated from poultry, including multidrug-resistant avian pathogenic E. coli as well as the reference strain ATCC 25922. GC-MS analysis demonstrated variation in the chemical composition of the EOs, with linalool (16.00–35.95%) and linalyl acetate (18.15–43.61%) identified as the major constituents. Determination of the minimum inhibitory concentration (MIC) by the broth microdilution method showed that pure linalool exhibited the strongest antibacterial activity (mean MIC = 0.31% v/v), followed by the EO from the lavender variety ‘Blue River’ (0.85% v/v), and the varieties ‘Maillette’ and ‘Ellagance Purple’ (0.98% and 1.00% v/v, respectively). Linalyl acetate had 5-fold lower antibacterial activity than linalool (1.63% v/v), whereas the weakest activity was observed for the variety ‘Matherone’ EO (4.50% v/v). Statistical analysis confirmed a significant correlation between higher linalool content and stronger antibacterial activity of the tested EOs against various strains of E. coli. Time–kill analysis showed that linalool and EOs with high linalool levels completely eliminated the multidrug-resistant E. coli strain within 4–8 h. EOs from L. angustifolia show potential as an alternative to conventional antibiotics in poultry production but their efficacy is highly dependent on the chemotype.