Ação antimicrobiana de diferentes terpenos e fenilpropanoides em Escherichia coli e Staphylococcus aureus

Abstract

Outbreaks of foodborne diseases are reported worldwide and affect thousands of people annually. The existence of microorganisms that are resistant to commercially available antibiotics generates the need to develop new agents capable of acting effectively in the control of these pathogens. In this scenario, the terpenoids and phenylpropanoids stand out because they have great biological activity and a broad spectrum of action. The objective of this study was to evaluate the antibacterial potential of six compounds derived from terpenes and phenylpropanoids (limonene, β-citronellol, carvone, carvacrol, eugenol and transcinnamaldehyde) and to investigate the mechanism of action of these compounds against the Escherichia coli and Staphylococcus aureus bacteria. Standards were purchased commercially. The bacteriostatic potential of the samples was determined by the macrodilution technique, and the bactericidal effect was confirmed by plating. The mechanism of the antibacterial action was studied on the basis of biological assays to verify the efflux of potassium ions, the decrease in the capacity for salt tolerance, extravasation of absorbent cellular contents in 260 nm and the absorption of crystal violet. The influence of the patterns on the morphology of E. coli and S. aureus was analyzed by scanning electron microscopy (SEM). Bacteriostatic and bactericidal effects were observed in both species, caused by the compounds carvone, carvacrol, eugenol and trans-cinnamaldehyde; however, the β-citronellol and limonene terpenes presented antibacterial activity only against S. aureus. None of the compounds tested caused potassium effusion from bacterial cells. A decrease in salt tolerance was observed for strains of E. coli treated with carvacrol and for S. aureus treated with β-citronellol. The carvone and transcinnamaldehyde standards increased the salt tolerance of S. aureus. The extravasation of cellular materials from the two microorganisms was induced by treatments with carvone, carvacrol, eugenol and trans-cinnamaldehyde. In turn, β-citronellol did not appear to affect the release of absorbent contents from S. aureus. Absorption of crystal violet by E. coli increased significantly after incubation with standards, whereas a slight decrease was observed for treated S. aureus cells. The images obtained by MEV demonstrate the morphological alterations caused in the microorganisms by the evaluated compounds. No rupture of the cell membrane was observed. It was concluded that the carvone, carvacrol, eugenol and trans-cinnamaldehyde standards presented biological activity against E. coli and S. aureus, and β-citronellol has an antibacterial potential only against S. aureus. The mechanism of action of these monoterpenes and phenylpropanoids seems to involve changes in membrane permeability, either directly or indirectly, but without resulting in cell lysis. Keywords: Secondary metabolites. Antibacterial mec