In vitro antibacterial activity of the essential oil of Ageratum conyzoides from the Brazilian Amazon

Natural products, specifically essential oils (EOs), have exhibited significant biological properties with potential medical applications. In this context, the aim of this study was to analyze the chemical composition and the antibacterial, antioxidant, and cytotoxic activities of the EO of Ageratum conyzoides from the municipality of Santa Rita, Maranhão, in the Brazilian Amazon. The EO was extracted from the fresh aerial parts of A. conyzoides L. using the hydrodistillation method and the oil was analyzed using a GCMS-QP2010 Ultra system. Standard strains of Listeria monocytogenes, Escherichia coli, Salmonella typhimurium, Bacillus cereus and Staphylococcus aureus were used to determine antibacterial activity using the minimum inhibitory concentration (MIC) method and minimum bactericidal concentration (MBC). The antioxidant potential of the EO of A. conyzoides was evaluated using 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2,2-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) free radical scavenging assays. The main constituents found in the oil were precocene I (79.85%) and (E)-caryophyllene (13.55%). The bacteriostatic efficacy of A. conyzoides EO's estimated by MIC and MBC was between 31.25 and 250 μg/mL. Gram-negative bacteria (S. typhimurium and E. coli) were the most resistant. The IC50 values obtained from the DPPH and ABTS assays were 287.94 ± 7.02 µg/mL and 132.23 ± 15.41 µg/mL, respectively. The results show that the essential oil of A. conyzoides has promising antibacterial activity, especially against Gram-positive bacteria.