Antimicrobial and Antibiofilm Properties of Lavandula stoechas Essential Oil: An Experimental Study

The rising global burden of antimicrobial resistance and biofilm-associated infections has intensified the search for effective plant-derived alternatives to conventional antimicrobial agents. However, the antimicrobial and antibiofilm properties of eucalyptol-rich Lavandula stoechas essential oil against clinically important bacterial and fungal pathogens remain insufficiently characterized. This study evaluated the antimicrobial activity, biofilm inhibition, and biofilm eradication efficacy of L. stoechas essential oil (LEO) against Staphylococcus aureus ATCC 25923, Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853, Acinetobacter baumannii ATCC 17987, Klebsiella pneumoniae ATCC 13883, and Candida albicans ATCC 90028. The chemical composition of LEO was characterized by gas chromatography–mass spectrometry (GC–MS). Antimicrobial activity was determined using the disk diffusion and broth microdilution (MIC) methods, with LEO tested over a concentration range of 3.33% to 0.2% (v/v), whereas biofilm inhibition and eradication were assessed using the microtiter plate assay at MIC/2 and at MIC and 2×MIC, respectively. GC–MS analysis revealed a distinct cineole–camphor chemotype, dominated by eucalyptol (1,8-cineole; 42.31%), camphor (26.4%), and camphene (8.49%), differing from the chemotypes most commonly reported in the literature. LEO produced the largest inhibition zone against the clinically important nosocomial pathogen A. baumannii (19.1 ± 0.5 mm), which was significantly greater than the zones of all other tested strains (one-way ANOVA, F(4,10) = 84.01, p < 0.0001; Tukey’s HSD, p < 0.05), whereas the lowest MIC value [0.2% (v/v)] was observed for C. albicans. In antibiofilm assays, the highest biofilm inhibition was observed for C. albicans (86%, at MIC). Against A. baumannii, LEO exhibited moderate antibiofilm activity, with biofilm inhibition ranging from 43.34% to 64% and biofilm eradication from 42.47% to 67.5%. For S. aureus, biofilm inhibition reached 60.15% at the MIC, while biofilm eradication ranged from 62.61% to 71.23%. Increasing the LEO concentration significantly enhanced biofilm inhibition (MIC/2 vs. MIC) in A. baumannii and C. albicans, and biofilm eradication (MIC vs. 2×MIC) in S. aureus, A. baumannii, and C. albicans (Welch’s t-test, p < 0.05). Overall, the eucalyptol-rich cineole–camphor chemotype of L. stoechas exhibited pathogen-specific antimicrobial and antibiofilm activities, particularly against A. baumannii and C. albicans. These findings provide preliminary in vitro evidence of its antimicrobial and antibiofilm potential, and further investigation using multidrug-resistant clinical isolates and in vivo models is recommended