Abstract
Considering the evidence that essential oils, as well as safrole, could modulate bacterial growth in different resistant strains, this study aims to characterize the phytochemical profile and evaluate the antibacterial and antibiotic-modulating properties of the essential oil Ocotea odorífera (EOOO) and safrole against efflux pump (EP)-carrying strains. The EOOO was extracted by hydrodistillation, and the phytochemical analysis was performed by gas chromatography coupled to mass spectrometry (GC-MS). The antibacterial and antibiotic-modulating activities of the EOOO and safrole against resistant strains of Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa were analyzed through the broth microdilution method. The EP-inhibiting potential of safrole in association with ethidium bromide or antibiotics was evaluated using the S. aureus 1199B and K2068 strains, which carry genes encoding efflux proteins associated with antibiotic resistance to norfloxacin and ciprofloxacin, respectively. A reduction in the MIC of ethidium bromide or antibiotics was used as a parameter of EP inhibition. The phytochemical analysis identified 16 different compounds in the EOOO including safrole as the principal constituent. While the EOOO and safrole exerted clinically relevant antibacterial effects against S. aureus only, they potentiated the antibacterial activity of norfloxacin against all strains evaluated by our study. The ethidium bromide and antibiotic assays using the strains of S. aureus SA1119B and K2068, as well as molecular docking analysis, indicated that safrole inhibits the NorA and MepA efflux pumps in S. aureus. In conclusion, Ocotea odorifera and safrole presented promising antibacterial and antibiotic-enhancing properties, which should be explored in the development of drugs to combat antibacterial resistance, especially in strains bearing genes encoding efflux proteins.
Highlights
Compounds generated by the secondary metabolism of plants constitute a large group of substances with significant structural and functional diversity, among which essential oils are notable bioactive compounds with antifungal, antiviral, antiprotozoal and antibacterial properties [1,2,3,4]
The extraction of the essential oil Ocotea odorífera (EOOO) by hydrodistillation presented a yield of 2.31%, considering the dry weight of the botanical material
Phytochemical analysis of the essential oil through gas chromatography coupled with mass spectrometry (GC-MS) identified 93.1% of the total constituents, revealing the presence of 16 different compounds, including safrole (77.9%), spathulenol (4.0%) and ortho-cymene
Summary
Compounds generated by the secondary metabolism of plants constitute a large group of substances with significant structural and functional diversity, among which essential oils are notable bioactive compounds with antifungal, antiviral, antiprotozoal and antibacterial properties [1,2,3,4]. Essential oils are complex mixtures of volatile and aromatic compounds found in a great variety of plant species, acting in defense against infections, parasites, and other stress conditions [5,6]. In this context, terpenes, which comprise the largest class of natural products, have been identified as very potent bioactive compounds [7]. Thymol and carvacrol are notable compounds with potent antimicrobial activities These monoterpenes have been found as major constituents of essential oils obtained from a wide variety of aromatic plants [8]. The essential oil of the leaves of Aloysia gratissima and Baccharis reticulata, which have 1,8-cineole, germacrene D, α-pinene, β-caryophyllene, and β -pinene as major constituents, demonstrated bactericidal activity against both Gram-positive (Staphylococcus aureus and Bacillus cereus) and Gram-negative (Escherichia coli and Pseudomonas aeruginosa) bacterial strains [9,10]
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