The chemical composition of the essential oils of Mentha arvensis and Mentha piperita and their antimicrobial activity against twelve Aeromonas spp. isolates from tambaquis (Colossoma macropomum), an important native farmed fish species in Brazil, were evaluated. The oils were characterized using gas chromatography and mass spectrometry (GC/MS) and their antimicrobial activity was evaluated through the microdilution method. The essential oils of these Mentha species mainly comprised oxygenated monoterpenes (97.1% for M. arvensis and 86.2% for M. piperita) and menthol was the major compound of these oils (86.1% for M. arvensis and 33.8% for M. piperita). It was confirmed that these oils had antimicrobial activity against 12 isolates of Aeromonas spp., with minimum inhibitory concentration (MIC) and minimum bacterial concentration (MBC) ranging from 1,250 to 16,666.7 μg mL⁻¹. Better antimicrobial activity was achieved by the M. arvensis essential oil.

The aim of this study was to evaluate the antimicrobial activity of Lippia sidoides, Ocimum gratissimum and Zingiber officinale‘s essential oils against Aeromonas spp. isolates from Colossoma macropomum, and to determine their chemical composition. Essential oils were obtained through hydrodistillation and their chemical composition analyzed using gas chromatography coupled to mass spectrometry. The antimicrobial activity of the oils was evaluated by minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC). The major compounds were thymol (76.6%), p-cymene (6.3%) and (E)- β-caryophyllene (5.0%) in L. sidoides; eugenol (43.3%), 1,8-cineole (28.2%) and β-selinene (5.5%) in O. gratissimum; and geranial (23.2%), neral (16.7%) and 1,8-cineole (15.8%) in Z. officinale. All the essential oils evaluated showed bactericidal action against isolates of Aeromonas spp., with MIC and MBC ranging from 625 to 5,000 μg mL⁻¹. We highlight the L. sidoides oil with the best antimicrobial activity (MIC and MBC ranging from 625 to 1,250 μg mL⁻¹).

The objective of this study was to evaluate the antimicrobial activity of the essential oils from five Brazilian Piper species (Piper aduncum, Piper callosum, Piper hispidinervum, Piper hispidum and Piper marginatum) against strains of Aeromonas hydrophila, isolated from tambaqui (Colossoma macropomum), as well as their chemical composition. The oils were characterized by gas chromatography and mass spectrometry (GC/MS), and the major compounds identified were: dillapiole (80.7 %) for P. aduncum; safrole (67.0 %), methyl-eugenol (7.2 %) and β-pinene (6.6 %) for P. callosum; safrole (89.3 %) for P. hispidinervum; γ-terpinene (27.3 %), p-cymene (14.0 %) and α-terpinene (12.0 %) for P. hispidum; δ-3-carene (13.1 %), propiopiperone (8.0 %) and (E)-caryophyllene (6.8 %) for P. marginatum. The Brazilian Piper species evaluated in this study were able to inhibit the growth of the ten strains of A. hydrophila, with minimum inhibitory concentration (MIC) values ranging from 234.37 to 30,000 μg mL^-1. The antimicrobial activity of Piper essential oils was considered strong for P. callosum, P. hispidinervum, P. hispidum and P. marginatum, with the exception of P. aduncum that presented weak activity for all strains. This is the first record of antimicrobial activity of Piper essential oils against strains of A. hydrophila isolated from tambaqui, suggesting the potential for use in the treatment of infections caused by this bacterium.

The antimicrobial activity of the essential oils from Lippia alba, Lippia sidoides, Mentha piperita, Ocimum gratissimum and Zingiber officinale was tested against Streptococcus agalactiae. The major compounds in the oils, identified by gas chromatography and mass spectrometry (GC/MS), were geranial (25.4%), neral (16.6%) and caryophyllene oxide (16.0%) in L. alba; thymol (76.6%), p-cymene (6.3%) and β-caryophyllene (5.0%) in L. sidoides; menthol (30.5%), menthyl acetate (14.6%), pulegone (14.2%) and menthone (12.9%) in M. piperita; eugenol (43.3%), 1,8-cineole (28.2%) and β-selinene (5.5%) in O. gratissimum; and geranial (23.2%), neral (16.7%) and 1,8-cineole (15.8%) in Z. officinale. All essential oils evaluated showed bactericidal action against S. agalactiae with minimum inhibitory concentration (MIC) ranging from 312.5–2,500 μg mL⁻¹ and minimum bactericidal concentration (MBC) ranging from 416.7–2,500 μg mL⁻¹. In this study, L. sidoides essential oil showed the better results against S. agalactiae.

In this study, we evaluated the chemical composition and the in vitro anthelmintic efficacy of the essential oils (EOs) of the plants Aloysia triphylla, Adenocalymna alliaceum, Allium sativum, Croton cajucara (white and red morphotypes), Curcuma longa, Lippia gracilis, Lippia origanoides, Ocimum gratissimum, Mentha arvensis, and Piper aduncum against the Acantocephalan Neoechinorhynchus buttnerae. The in vitro viability of worms was observed after 24 h-exposure to nine concentrations of EOs from each plant. Lower EC₅₀ values were obtained for M. arvensis, L. origanoides, L. gracilis, C. cajucara (red and white morphotypes), O. gratissimum, and P. aduncum. All EOs showed 100% anthelmintic efficacy in vitro in 24 h. In regard to damage to the integument of helminths, edema in the lacunar spaces with formation of bubbles in the subcuticle, body swelling, increased volume of the pseudocelomatic cavity and degeneration of the reproductive organs were observed after exposure to A. triphylla OE.