RESUMO
The increasing bacterial resistance to antibiotics is a worldwide concern. Essential oils are known to possess remarkable antibacterial properties, but their high chemical variability complicates their development into new antibacterial agents. Therefore, the main purpose of this study was to standardize their chemical composition. Several commercial essential oils of ajowan (Trachyspermum ammi L.) and thyme (chemotype thymol) (Thymus vulgaris L.) were bought on the market. GC-MS analysis revealed that thyme essential oils have a chemical composition far more consistent than ajowan essential oils. Sometimes thymol was not even the major compound. The most abundant compounds and the homemade mixtures were tested against two Staphylococcus aureus strains. The antibacterial property of ß-caryophyllene presented no direct activity against S. aureus LMG 15975, but in association with thymol or carvacrol at equal percentages an MIC of 125 µg/mL was observed. The mixture of those three compounds at equivalent percentages also decreased by 16-fold the MIC of the penicillin V. Against S. aureus LMG 21674, ß-caryophyllene presented an MIC of 31.3 µg/mL and decreased by 267-fold the MIC of the penicillin V. These observations led us to question the benefits of using a complex chemical mixture instead of one active compound to fight bacterial resistance.
RESUMO
OBJECTIVE@#To investigate the chemical composition of a moderately polar extract (CHCl3 soluble part of the MeOH-H2O extract) obtained from the aerial parts (leaves and flowers) of Centaurea diluta Ait. subsp. algeriensis (Coss. & Dur.) Maire, a species endemic to Algeria and Morocco on which no reports are available to date. To evaluate in vitro the cytotoxic, antifungal and antimicrobial activities of this extract and the cytotoxic and antimicrobial activities of its isolated secondary metabolites.@*METHODS@#The cytotoxic effects of the extract were investigated on 3 human cancer cell lines i.e. the A549 non-small-cell lung carcinoma (NSCLC), the MCF7 breast adenocarcinoma and the U373 glioblastoma using a MTT colorimetric assay. Biological data allowed to guide the fractionation of the extract by separation and purification on silica gel 60 (CC and TLC). The isolated compounds which were characterized by spectral analysis, mainly HR-ESIMS, HR-EIMS, UV and NMR experiments ((1)H, (13)C, COSY, ROESY, HSQC and HMBC) and comparison of their spectroscopic data with those reported in the literature, were evaluated for cytotoxic activities on six cancer cell lines (A549, MCF7, U373, Hs683 human glioma, PC3 human prostate and B16-F10 murine melanoma). The direct and indirect antibacterial and antifungal activities were determined using microdilution methods for the raw extract and TLC-bioautography and microdilution methods against standard and clinical strains for the isolated compounds.@*RESULTS@#The raw extract reduced cell viability with IC50s of 27, 25 and 21 μg/mL on A549, MCF7 and U373, respectively. Five secondary metabolites: two phenolic compounds (vanillin 1, paridol 3), a lignan [(-)-arctigenin 2] and two flavonoid aglycones (eupatilin 4 and jaceosidin 5), were then isolated from this extract. Moderate cytotoxic effects were observed for (-)-arctigenin 2 (IC50s: 28 and 33 μM on Hs683 and B16-F10, respectively), eupatilin 4 (IC50s: 33 and 47 μM on B16-F10 and PC3, respectively) and jaceosidin 5 (IC50s: 32 and 40 μM on PC3 and B16-F10, respectively).@*CONCLUSIONS@#All the isolated compounds were described for the first time from this species. Although inactive against 7 tested microorganisms (fungi, bacteria and yeast, human or plant pathogens), the raw extract was able to potentiate the effect of beta-lactam antibiotics on methicillin-resistant Staphylococcus aureus (MRSA), reducing the minimal inhibitory concentrations (MICs) by a factor of 2-32-fold. No synergy was found between the extract and streptomycin. From the five isolated compounds only jaseosidin 5 showed a moderate antimicrobial activity.
RESUMO
Objective To investigate the chemical composition of a moderately polar extract (CHCl
