Caracterização química e atividade antimicrobiana de óleos essenciais de Croton grewioides Baill. sobre o fitopatógeno Xanthomonas campestris pv. campestris

Abstract

Croton grewioides Baill. (Alecrim-de-cabocla) is an endemic species from Brazil and occurs in the states of Alagoas, Bahia, Paraíba, Pernambuco, Rio Grande do Norte, Minas Gerais, Goiás, and Sergipe. It is an aromatic, essential oil-producing plant that has bioactive properties, including antioxidant, antifungal and insecticidal activities. Germplasm Banks (BAGs) are extremely important for the conservation of the genetic variability of aromatic species, and the chemical characterization is essential for the prospecting of bioactive compounds. The search for such compounds corroborates with the identification of biological activities, such as have been described for different species of the Croton genus due to the diversity of chemical composition observed in their essential oils. The objective of this work was to carry out the chemical characterization of essential oils from accessions of Croton grewioides Baill. of the Active Germplasm Bank of Medicinal and Aromatic Plants of UFS, and to evaluate their in vitro antibacterial activity on Xanthomonas campestris pv. campestri. The essential oils from 29 accessions of C. grewioides were extracted by the hydrodistillation method and analyzed by Gas Chromatography coupled to Mass Spectrometry (GC/MS). To determine the minimum inhibitory (MIC) and minimum bactericidal (MBC) Concentrations of the essential oils, the microdilution method was used. Essential oils and the marjoritarian compound eugenol concentrations ranged from 125 to 4000 µg.mL-1 . As a positive control, streptomycin sulfate (12.5 to 100 µg.mL-1 ) was used. The growth kinetics were evaluated for different concentrations of the essential oil (2 ×, 1 ×, 1/2 ×, 1/4 × and 1/8 × MIC) considering the times: 5, 10, 15, 30, 45, 60, 90, 120 and 180 min. In the membrane permeability assay with Propidium Iodide (PI), the bacteria were exposed to the essential oil at the same concentrations and times used for the growth kinetic assay. The major compounds identified in the analyzed essential oils were eugenol, methyl eugenol, and methyl chavicol. The essential oil CGR 108 had a MIC of 1000 µg.mL-1 , while the MBC was 2000 µg.mL-1 . The MIC and MBC values for the essential oil CGR 107 were 2000 µg.mL-1 . The essential oil CGR 125 had MIC and MBC of 2000 and 4000 µg.mL-1 , respectively. For CGR 318, the MIC was 4000 µg.mL-1 and MBC was > 4000 µg.mL-1 . For CGR 209 there was no antibacterial activity at the concentrations tested. For the compound eugenol, the MIC and MBC were 500 and 1000 µg.mL-1 , respectively. In the growth kinetics, for the essential oil CGR 108, with 30 minutes a reduction in optical density was observed for the 2 × and 1 × MIC concentrations. The highest fluorescence intensity with PI was observed when bacteria were exposed to 2 × and 1 × MIC concentrations after 30 minutes. The essential oils of Croton grewioides Baill. and eugenol compound have antibacterial potential against Xanthomonas campestris pv. campestris.