Efficacy of lavender essential oil against respiratory tract bacteria is influenced by harvesting time

Antibiotic resistance can be largely associated with the biofilm-forming properties of bacteria, since in this form pathogens show increased resistance to antibiotics and disinfectants. Pathogens, for example the airway colonizing Pseudomonas aeruginosa , Streptococcus pneumoniae and the members of the genus Haemophilus , are frequently arranged in a biofilm on the mucous membrane. Essential oils are increasingly used both for prevention of diseases and in complementary therapies. This study investigated the composition and antimicrobial activities of Lavandula angustifolia Mill. essential oil (LEO) distilled from flowers collected before, during and after the flowering period. Our results confirm that collection time significantly influences the composition and antibacterial activity of LEO. The most active sample was LEO distilled before flowering period in each experimental setup. The most resistant pathogen was P. aeruginosa (MIC: 2.5 mg/mL), while the most sensitive was S. pneumoniae (MIC: 0.5 mg/mL). In the biofilm experiment, too, LEO from the pre-bloom period was the most effective. Its anti-biofilm activity decreased in parallel with increasing incubation time (4, 6, 8, 12, 24 h). In summary, we demonstrated the antimicrobial effectiveness of LEOs against respiratory pathogens in biofilms of different maturity, and LEO distilled before flowering exhibited the strongest biofilm inhibition.