Acaricidal activity of the essential oils from Leptospermum scoparium, Origanum vulgare and Litsea cubeba on Rhipicephalus microplus: Influence of the solvents and search for fractions with higher bioactivity.

The use of natural products in research on tick control for Rhipicephalus microplus is increasing year by year, with promising results. In this regard, the aim of the present study was to phytochemically characterize the essential oils (EOs) of Leptospermum scoparium, Origanum vulgare and Litsea cubeba, and to evaluate the acaricidal activity of these EOs in solutions prepared using ethanol, dimethylsulfoxide (DMSO) and Tween 80 on larvae and females of R. microplus. In addition, three L. scoparium fractions were also isolated and their acaricidal activity on these larvae and adult females was tested. Gas chromatography and mass spectrometry results showed that cis-calamenene (29.82 %), carvacrol (64.85 %) and geranial (42.44 %) were the majority compounds of L. scoparium, O. vulgare and L. cubeba, respectively. Three fractions were isolated from L. scoparium: A1, rich in sesquiterpene hydrocarbons, and A2 and A3, rich in ß-triketones. Bioassays on unfed larvae (immersion test) were performed using all the EOs at concentrations from 2.5 to 10.0 mg/mL; and using the three fractions obtained from L. scoparium EO at concentrations from 0.625 to 10 mg/mL. We observed 100 % mortality of larvae in all treatments with L. scoparium EO at all concentrations (diluted both in DMSO and in ethanol), and in treatments with O. vulgare EO diluted in DMSO. However, L. cubeba EO only gave rise to more than 99 % mortality at a concentration of 10 mg/mL, using the same solvents. For engorged females, the immersion test was performed at concentrations from 2.5 to 10.0 mg/mL. Percentage control greater than 90 % was observed only at the highest concentrations of L. scoparium and O. vulgare EOs diluted in DMSO and ethanol, while L. cubeba EO did not reach 90 % control in any of the treatments. In tests on L. scoparium fractions, larval mortality in the fractions rich in ß-triketones (A2 and A3) was above 97 % at a concentration of 2.5 mg/mL, while in the A1 fraction, rich in sesquiterpene hydrocarbons, at the same concentration (2.5 mg/mL), mortality did not reach 22 %. In the adult immersion test, the percentage control was higher than 98 % at the lowest concentration (2.5 mg/mL) of the A1 fraction, while in the treatments with the fractions A2 and A3, the control levels were 16 and 50 %, respectively. Thus, we can conclude that the EOs of L. scoparium, O. vulgare and L. cubeba have acaricidal activity on R. microplus, as also do the fractions derived from L. scoparium EO.

Anti-Staphylococcal Activity of Cinnamomum zeylanicum Essential Oil against Planktonic and Biofilm Cells Isolated from Canine Otological Infections.

The aim of this study was to evaluate the phytochemical profile of Cinnamomum zeylanicum essential oil (CZEO) and their antimicrobial and antibiofilm activity against Staphylococcus strains isolated from canine otitis. First, the CZEO chemical composition was determined by gas chromatography-mass spectrometry (CG-MS). External otitis samples collected from dogs were submitted to staphylococcal isolation, followed by MALDI-TOF mass spectrometry identification. The antimicrobial action was tested against the isolates using the disk-diffusion and microdilution methods. The antibiofilm activity was evaluated by CZEO-based concentrations, subMIC for biofilm formation and supraMIC against preformed biofilm, quantified by crystal violet (CV) staining and CFU counting. The chemical analysis revealed that (E)-cinnamaldehyde, eugenol and (E)-cinnamyl acetate were the main compounds in the CZEO, representing 77.42, 8.17 and 4.50%, respectively. Two strains of three different species, S. saprophyticus, S. schleiferi and S. pseudintermedius, were identified. The disk-diffusion test showed an inhibitory zone diameter, ranging from 34.0 to 49.5 mm, while the MIC and MBC values were around 500 and 1000 µg/mL. SubMIC demonstrated an inhibition on biofilm formation against 4 out the 6 strains tested. On mature biofilm, the CZEO-based supraMIC groups had slightly change on biomass, however, the biofilm cell viability decreased the CFU in 3 magnitude orders.

Chemical Composition and Antimicrobial Effectiveness of Ocimum gratissimum L. Essential Oil Against Multidrug-Resistant Isolates of Staphylococcus aureus and Escherichia coli.

The study investigated the antimicrobial activity of the essential oil extract of Ocimum gratissimum L. (EOOG) against multiresistant microorganisms in planktonic and biofilm form. Hydrodistillation was used to obtain the EOOG, and the analysis of chemical composition was done by gas chromatography coupled with mass spectrometry (GC/MS) and flame ionization detection (GC/FID). EOOG biological activity was verified against isolates of Staphylococcus aureus and Escherichia coli, using four strains for each species. The antibacterial action of EOOG was determined by disk diffusion, microdilution (MIC/MBC), growth curve under sub-MIC exposure, and the combinatorial activity with ciprofloxacin (CIP) and oxacillin (OXA) were determined by checkerboard assay. The EOOG antibiofilm action was performed against the established biofilm and analyzed by crystal violet, colony-forming unit count, and SEM analyses. EOOG yielded 1.66% w/w, with eugenol as the major component (74.83%). The MIC was 1000 µg/mL for the most tested strains. The growth curve showed a lag phase delay for both species, mainly S. aureus, and reduced the growth level of E. coli by half. The combination of EOOG with OXA and CIP led to an additive action for S. aureus. A significant reduction in biofilm biomass and cell viability was verified for S. aureus and E. coli. In conclusion, EOOG has relevant potential as a natural alternative to treat infections caused by multiresistant strains.