Introduction

Antimicrobial resistance became a major worldwide threat. Research have been focused recently on the reassessment of natural products as molecules with high biological and chemical potential. We aimed to study the efficacy of several extracts and essential oils with less known antimicrobial potential.

Method

Antimicrobial and antibiofilm activities of Ocimum basilicum and Eugenia caryophyllus essential oils dissolved in DMSO 1% on two multidrug-resistant bacterial strains of S. aureus ES5168 and E. coli ES5649 and antimicrobial activity of Ocimum basilicum, Robinia pseudocacia, Allium arsinum, Artemisia absinthium, Equisetum arvense alchoolic extracts on four multidrug-resistant bacterial strains of S. aureus ES5168, RC0831 and E. coli ES5649, CA0422 were tested. All bacterial strains exhibited resistance phenotype by a series of cumulative mechanisms. The essential oils and the plant extracts were analyzed by GC-MS. Antibacterial activity was evaluated using the microdilutions technique and anti-biofilm activity by crystal violet-based microtiter plate assay.

Results

Ocimum basilicum essential oil had no inhibitory effect on the S. aureus culture and biofilm. Both essential oils elicited values of 8 mg/ml on the E. coli and this concentration also had the higher inhibiting action on biofilm formation. All the tested extracts inhibited bacterial growth, although in the case of E. Coli no extract caused inhibition rates higher than 50%, while the Equisetum arvense led to a high inhibition rate of S. aureus, 79.06% and 80.32% respectively.

Conclusions

Even though the antimicrobial effect of plant extracts on the multidrug-resistant bacteria is not very high in all cases, the Equisetum arvense extract, a plant less used for its antibacterial properties, strongly inhibits the S. aureus strains both in culture and biofilms.