Inhibition and eradication effects of Thymus leptobotrys and Thymus satureioïdes essential oils against multidrug resistant Acinetobacter baumannii biofilms

In the present study, the antibacterial activity of Thymus leptobotrys and Thymus satureioïdes essential oils was evaluated against nine multidrug resistant Acinetobacter baumannii strains. Besides, their inhibition and eradication effects were investigated, for the first time, against the biofilm form of the tested multidrug resistant bacteria. Gas chromatography–mass spectrometry analysis of the targeted essential oils highlighted the predominance of carvacrol and borneol, respectively. Their antibacterial activity test revealed considerable inhibition zones’ diameters (p < 0.05), ranging from 35 ± 1.4 to 43.6 ± 0.5 mm (Thymus leptobotrys) and from 16.6 ± 1.5 to 22 ± 2.8 mm (Thymus satureioïdes). Very low minimal inhibitory and bactericidal concentrations (p < 0.05) were also noted, varying from 0.78 to 12.5 mg/mL. Four strains out of nine (Acinetobacter baumannii 6, Acinetobacter baumannii 7, Acinetobacter baumannii 8, Acinetobacter baumannii 9) considered as the strongest biofilm producers by congo red agar and crystal violet methods, were chosen for the evaluation of biofilm inhibition and eradication effects of Thymus leptobotrys and Thymus satureioïdes essential oils. Great biofilm inhibition percentages were noted with 90.20% (Thymus satureioïdes) and 97.27% (Thymus leptobotrys) as the highest rates. Forty-eight hours biofilms were more resistant to the essential oils’ action. Low eradication proportions were observed ranging from 0 to 49%. Thus, Thymus leptobotrys and Thymus satureioïdes essential oils could be considered as a natural source of bioactive molecules and used as an alternative approach to prevent biofilm formation of multidrug resistant Acinetobacter baumannii.