Screening of Antibacterial and Antibiofilm Activities of Commercially Available Essential Oils' Different Samples in Comparison to Conventional Antibiotics

Abstract

Essential oils (EOs) have gained economic importance due to their biological activities, and increasing amounts are demanded everywhere. However, substantial differences between the same essential oil samples from different suppliers are reported due to numerous companies involved in EOs production and the continuous development of online sales. The present study investigates the antibacterial and antibiofilm activities of 2-4 samples of five commercially available essential oils (Oregano, Eucalyptus, Rosemary, Clove, and Peppermint oils) from different manufacturers. Their effects were evaluated in vitro on Gram-positive and Gram-negative bacteria (Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa). The antibacterial efficacy (ABE%) and antibiofilm efficacy (ABfE%) were determined spectrophotometrically at 562 and 570 nm using microplate cultivation techniques. The essential oils' calculated parameters were compared with those of three standard broad-spectrum antibiotics: Amoxicillin/Clavulanic acid (AMC), Gentamycin (GEN), and Streptomycin (STR), active on tested bacteria. The results showed that at the first dilution (D1 = 2.5 mg/mL), all essential oils (EOs) exhibited antibacterial activity against Gram-positive and Gram-negative bacteria. On S. aureus and E. coli, EOs had considerable antibacterial effects (ABE = 79.70—92.80%, respectively, 71.30 ‒ 94.00%). The highest antibacterial effects of commercially available EOs were against P. aeruginosa because all exhibited a significant antibiofilm activity. Their antibiofilm efficacy intensively decreased on E. coli and S. aureus. Generally, the samples with different manufacturers of the same EO showed similar effects. Only Clove and Peppermint oils samples displayed a higher variability associated with active metabolites' different contents, maybe due to various zones of harvesting raw material, numerous technologies involved in EOs obtaining processes, and complex interactions between components.