Recent Advances in the Application of Antibacterial Complexes Using Essential Oils.
ABSTRACT: Although antibacterial spectrum of essential oils (EOs) has been analyzed along with consumers' needs on natural biocides, singular treatments generally require high concentration of EOs and long-term exposures to eliminate target bacteria. To overcome these limitations, antibacterial complex has been developed and this review analyzed previous reports regarding the combined antibacterial effects of EOs. Since unexpectable combined effects (synergism or antagonism) can be derived from the treatment of antibacterial complex, synergistic and antagonistic combinations have been identified to improve the treatment efficiency and to avoid the overestimation of bactericidal efficacy, respectively. Although antibacterial mechanism of EOs is not yet clearly revealed, mode of action regarding synergistic effects especially for the elimination of pathogens by using low quantity of EOs with short-term exposure was reported. Whereas comprehensive analysis on previous literatures for EO-based disinfectant products implies that the composition of constituents in antibacterial complexes is variable and thus analyzing the impact of constituting substances (e.g., surfactant, emulsifier) on antibacterial effects is further needed. This review provides practical information regarding advances in the EO-based combined treatment technologies and highlights the importance of following researches on the interaction of constituents in antibacterial complex to clarify the mechanisms of antibacterial synergism and/or antagonism.
Project description:Laurus nobilis L. (laurel, Lauraceae) and Prunus armeniaca L. (apricot, Rosaceae) are important industrial crops and display significant biological properties, including antimicrobial activity. In this work, essential oils (EOs) prepared from the leaves of both species from Morocco were evaluated for the first time for possible synergistic in vitro antibacterial and antifungal effects with some conventional antimicrobial drugs, namely fluconazole, ciprofloxacin and vancomycin. Samples were further evaluated for chemical composition by gas chromatography-mass spectrometry (GC-MS). The main volatile compounds detected in L. nobilis were eucalyptol (40.85%), ?-terpinyl acetate (12.64%) and methyl eugenol (8.72%), while P. armeniaca was dominated essentially by (Z)-phytol (27.18%), pentacosane (15.11%), nonacosane (8.76%) and benzaldehyde (7.25%). Regarding antimicrobial activity, both EOs inhibited significantly all the microorganisms tested. The EO from L. nobilis had the highest activity, with minimal inhibitory concentrations (MICs) ranging from 1.39 to 22.2 mg/mL for bacteria and between 2.77 and 5.55 mg/mL for yeasts. Conversely, the combination of the studied EOs with ciprofloxacin, vancomycin and fluconazol resulted in a noteworthy decrease in their individual MICs. In fact, of the 32 interactions tested, 23 (71.87%) demonstrated total synergism and 9 (28.12%) a partial synergistic interaction. The EO from L. nobilis exhibited the highest synergistic effect with all the antibiotics used, with fractional inhibitory concentration (FIC) index values in the range of 0.266 to 0.75 for bacteria, and between 0.258 and 0.266 for yeast. The synergistic interaction between the studied EOs and standard antibiotics may constitute promising anti-infective agents useful for treating diseases induced by antibiotic-resistant pathogens.
Project description:Pinus eldarica (Pinaceae), an evergreen plant, is distributed across the warm and dry climates of western Asia, including Asia Minor, the Middle East, and land surrounding the Caspian Sea. Essential oils (EOs) from different aerial parts of this tree have been used in traditional medicine. We aimed to investigate the chemical profile and antimicrobial activity of the EO from P. eldarica grown in northwestern Iran. EO from the needles, bark, and pollen were extracted with boiling water using a Clevenger apparatus at yield of 0.7-1.2 cm3/100 g of dry plant material. The main chemical components of the EO from the needles were D-germacrene (18.17%), caryophyllene (15.42%), γ-terpinene (12.96%), and β-pinene (10.62%); those from the bark were limonene (16.99%), caryophyllene oxide (13.22%), and drimenol (13.2%); and those from the pollen were α-pinene (25.64%) and limonene (19.94%). In total, 83 constituents were characterized in the EOs, using gas chromatography mass spectrometry analysis; mainly, sesquiterpene hydrocarbons in needle EO and monoterpene hydrocarbons in pollen and bark EOs. β-Pinene, β-myrcene, limonene, and caryophyllene were identified in the EOs from all three plant parts. The antibacterial and antifungal properties of the EOs were examined: pollen EO exhibited antibacterial activity against Escherichia coli; bark EO inhibited the growth of Candida albicans and Staphylococcus aureus; and the needle EO inhibited the growth of S. aureus. Thus, the EOs from aerial parts of P. eldarica can benefit the EO industry and antibiotic development.
Project description:Essential oils (EOs) have gained increasing interest as a low-toxic, eco-friendly alternative to synthetic repellents and insecticides against insect pests. However, they have scarce practical application in the protection of stored grain because of their limited efficacy and their interference with the organoleptic properties of the grain. In this study, we evaluated the olfactory profile of the EOs of Foeniculum vulgare, Pistacia lentiscus, and Ocimum basilicum, and their toxicity against the main stored grain pest Sitophilus granarius. Trained assessors identified O. basilicum and F. vulgare, as more suitable than the P. lentiscus EO for the wheat treatment. In laboratory tests, the most toxic EO was the P. lentiscus (LC50 = 36.36 μL∙kg-1) while, the least toxic, was the F. vulgare one (LC50 = 77.59 μL∙kg-1). The EOs were also tested combined with diatomaceous earths (DEs) showing synergistic effects (co-toxicity coefficient values ranging from 1.36 to 3.35 for O. basilicum and F. vulgare EOs, respectively). Overall, O. basilicum resulted as the best EO for the wheat treatment, considering its insect toxicity and olfactory profile. In real storage conditions, the wheat co-treated with O. basilicum EO and DEs showed a significantly lower mean infestation (1.5 insect kg-1) than the non-treated wheat (7.0 insect kg-1).
Project description:Antibiotics are becoming ineffective against resistant bacteria. The use of essential oils (EOs) may constitute an alternative solution to fight against multidrug-resistant bacteria. This study aims to determine the chemical composition of EOs from five populations of the endemic Algerian Origanum glandulosum Desf. and to investigate their potential antibacterial activity against multidrug-resistant uropathogenic E. coli strains. The EOs were obtained by hydrodistillation and their composition was investigated by gas chromatography/mass spectrometry (GC/MS). The antibacterial activity was evaluated by the disc diffusion method against eight E. coli strains (six uropathogenic resistant and two referenced susceptible strains). Minimum inhibitory and bactericidal concentrations (MIC/MBC) were obtained by the broth microdilution method. The main EO components were thymol (15.2-56.4%), carvacrol (2.8-59.6%), ?-terpinene (9.9-21.8%) and p-cymene (8.5-13.9%). The antibacterial tests showed that all the EOs were active against all the strains, including the multidrug-resistant strains. The EO from the Bordj location, which contained the highest amount of carvacrol (59.6%), showed the highest antibacterial activity (inhibition diameters from 12 to 24.5 mm at a dilution of 1/10). To our knowledge, this is the first description of the activity of O. glandulosum EOs against resistant uropathogenic strains. Our study suggests that O. glandulosum EO could be used in some clinical situations to treat or prevent infections (e.g., urinary tract infections) with multidrug-resistant strains.
Project description:Type 2 diabetes mellitus (T2DM) is a metabolic disorder characterized by unpaired blood glycaemia maintenance. T2DM can be treated by inhibiting carbohydrate hydrolyzing enzymes (?-amylases and ?-glucosidases) to decrease postprandial hyperglycemia. Acarbose and voglibose are inhibitors used in clinical practice. However, these drugs are associated with unpleasant gastrointestinal side effects. This study explores new ?-amylase inhibitors deriving from plant volatile specialized metabolites. Sixty-two essential oils (EOs) from different plant species and botanical families were subjected to ?-amylase in vitro enzymatic assay and chemically characterized using gas chromatography coupled to mass spectrometry. Several EOs were found to be potential ?-amylase inhibitors, and Eucalyptus radiata, Laurus nobilis, and Myristicafragrans EOs displayed inhibitory capacities comparable to that of the positive control (i.e., acarbose). A bio-guided fractionation approach was adopted to isolate and identify the active fractions/compounds of Eucalyptus radiata and Myristica fragrans EOs. The bio-guided fractionation revealed that EOs ?-amylase inhibitory activity is often the result of antagonist, additive, or synergistic interactions among their bioactive constituents and led to the identification of 1,8-cineole, 4-terpineol, ?-terpineol, ?-pinene, and ?-pinene as bioactive compounds, also confirmed when they were tested singularly. These results demonstrate that EO oils are a promising source of potential ?-amylase inhibitors.
Project description:Plants are considered green resources for thousands of bioactive compounds. Essential oils (EOs) are an important class of secondary compounds with various biological activities, including allelopathic and antimicrobial activities. Herein, the present study aimed to compare the chemical profiles of the EOs of the widely distributed medicinal plant Calotropis procera collected from Saudi Arabia and Egypt. In addition, this study also aimed to assess their allelopathic and antimicrobial activities. The EOs from Egyptian and Saudi ecospecies were extracted by hydrodistillation and analyzed via GC-MS. The correlation between the analyzed EOs and those published from Egypt, India, and Nigeria was assessed by principal component analysis (PCA) and agglomerative hierarchical clustering (AHC). The allelopathic activity of the extracted EOs was tested against two weeds (Bidens pilosa and Dactyloctenium aegyptium). Moreover, the EOs were tested for antimicrobial activity against seven bacterial and two fungal strains. Ninety compounds were identified from both ecospecies, where 76 compounds were recorded in Saudi ecospecies and 33 in the Egyptian one. Terpenes were recorded as the main components along with hydrocarbons, aromatics, and carotenoids. The sesquiterpenes (54.07%) were the most abundant component of EO of the Saudi sample, while the diterpenes (44.82%) represented the mains of the Egyptian one. Hinesol (13.50%), trans-chrysanthenyl acetate (12.33%), 1,4-trans-1,7-cis-acorenone (7.62%), phytol (8.73%), and myristicin (6.13%) were found as the major constituents of EO of the Saudi sample, while phytol (38.02%), n-docosane (6.86%), linoleic acid (6.36%), n-pentacosane (6.31%), and bicyclogermacrene (4.37%) represented the main compounds of the Egyptian one. It was evident that the EOs of both ecospecies had potent phytotoxic activity against the two tested weeds, while the EO of the Egyptian ecospecies was more effective, particularly on the weed D. aegyptium. Moreover, the EOs showed substantial antibacterial and antifungal activities. The present study revealed that the EOs of Egyptian and Saudi ecospecies were different in quality and quantity, which could be attributed to the variant environmental and climatic conditions. The EOs of both ecospecies showed significant allelopathic and antimicrobial activity; therefore, these EOs could be considered as potential green eco-friendly resources for weed and microbe control, considering that this plant is widely grown in arid habitats.
Project description:Cutaneous myiasis is a severe worldwide medical and veterinary issue. In this trial the essential oil (EO) of the Andean medicinal plant species Clinopodium nubigenum (Kunth) Kuntze was evaluated for its bioactivity against the myiasis-inducing blowfly Lucilia sericata (Meigen) (Diptera Calliphoridae) and compared with that of the well-known medicinal plant species Lavandula angustifolia Mill. The EOs were analysed and tested in laboratory for their oviposition deterrence and toxicity against L. sericata adults. The physiology of EO toxicity was evaluated by enzymatic inhibition tests. The antibacterial and antifungal properties of the EOs were tested as well. At 0.8 ?L cm-2, both EOs completely deterred L. sericata oviposition up to 3 hours. After 24 h, the oviposition deterrence was still 82.7% for L. angustifolia and the 89.5% for C. nubigenum. The two EOs were also toxic to eggs and adults of L. sericata. By contact/fumigation, the EOs, the LC50 values against the eggs were 0.07 and 0.48 ?L cm-2 while, by topical application on the adults, LD50 values were 0.278 and 0.393 ?L per individual for C. nubigenum and L. angustifolia EOs, respectively. Inhibition of acetylcholine esterase of L. sericata by EOs (IC50 = 67.450 and 79.495 mg L-1 for C. nubigenum and L. angustifolia, respectively) suggested that the neural sites are targets of the EO toxicity. Finally, the observed antibacterial and antifungal properties of C. nubigenum and L. angustifolia EOs suggest that they could also help prevent secondary infections.
Project description:The aim of this study was to analyze the antibacterial activity of four essential oils (EOs), Melaleuca alternifolia, Eucalyptus globulus, Mentha piperita, and Thymus vulgaris, in preventing the development and spread of extended-spectrum ?-lactamase (ESBL)-producing Escherichia coli and Klebsiella pneumoniae, metallo-beta-lactamase (MBL)-producing Pseudomonas aeruginosa and carbapenemase (KPC)-producing Klebsiella pneumoniae. A total of 60 strains were obtained from the stock collection from the Microbiology Laboratory of Hesperia Hospital, Modena, Italy. Twenty ESBL-producing E. coli, 5 K. pneumoniae, 13 KPC-producing K. pneumoniae, and 20 MBL-producing P. aeruginosa were cultured and reconfirmed as ESBL and carbapenamase producers. Polymerase chain reaction was used for the detection of genes responsible for antibiotic resistance (ESBL and KPC/MBL). Antibacterial activity of the EOs was determined using the agar disk diffusion assay, and minimal inhibitory concentrations (MICs) were also evaluated. Lastly, adhesion capability and biofilm formation on polystyrene and glass surfaces were studied in 24 randomly selected strains. M. alternifolia and T. vulgaris EOs showed the best antibacterial activity against all tested strains and, as revealed by agar disk diffusion assay, M. alternifolia was the most effective, even at low concentrations. This effect was also confirmed by MICs, with values ranging from 0.5 to 16 µg/mL and from 1 to 16 µg/mL, for M. alternifolia and T. vulgaris EOs, respectively. The EOs' antibacterial activity compared to antibiotics confirmed M. alternifolia EO as the best antibacterial agent. T. vulgaris EO also showed a good antibacterial activity with MICs lower than both reference antibiotics. Lastly, a significant anti-biofilm activity was observed for the two EOs (*P < 0.05 and **P < 0.01 for M. alternifolia and T. vulgaris EOs, respectively). A good antibacterial and anti-biofilm activity of M. alternifolia and T. vulgaris EOs against all selected strains was observed, thus demonstrating a future possible use of these EOs to treat infections caused by ESBL/carbapenemase-producing strains, even in association with antibiotics.
Project description:The present study aimed to evaluate the synergistic effects of the crude ethyl acetate extract (CEAE) from endophytic actinomycete MPT42 and essential oil (EO) of the same host plant Litsea cubeba. The isolate MPT42, exhibiting broad-spectrum antimicrobial activities and harboring all three antibiotic-related biosynthetic genes pks-I, pks-II, and nrps, was identified as Streptomycete griseorubens based on an analysis of the morphology, physiology, and 16S rDNA sequence. Minimum inhibitory concentrations (MICs) and the fractional inhibitory concentration index were used to estimate the synergistic effects of various combined ratios between CEAE or antibiotics (erythromycin, vancomycin) and EO toward 13 microbial strains including pathogens. L. cubeba fruit EO, showing the main chemical constituents of 36.0% citral, 29.6% carveol, and 20.5% limonene, revealed an active-low against tested microbes (MICs ? 600 ?g/mL). The CEAE of S. griseorubens culture exhibited moderate-strong antimicrobial activities against microbes (MICs = 80-600 ?g/mL). Analysis of the mechanism of action of EO on Escherichia coli ATCC 25922 found that bacterial cells were dead after 7 h of the EO treatment at 1 MIC (5.5 mg/mL), where 62% cells were permeabilized after 2 h and 3% of them were filament (length ? 6 ?m). Combinations of CEAE, erythromycin, or vancomycin with EO led to significant synergistic antimicrobial effects against microbes with 4-16 fold reduction in MIC values when compared to their single use. Interestingly, the vancomycin-EO combinations exhibited a strong synergistic effect against five Gram-negative bacterial species. This could assume that the synergy was possibly due to increasing the cell membrane permeability by the EO acting on the bacterial cells, which allows the uptake and diffusion of antimicrobial substances inside the cell easily. These findings in the present study therefore propose a possible alternative to combat the emergence of multidrug-resistant microbes in veterinary and clinics.
Project description:This study investigated the effects of dietary essential oils (EOs) on intestinal microbial composition and metabolic profiles in weaned piglets. The piglets were fed the same basal diet supplemented with EOs (EO) or without EOs (Con) in the current study. The results showed that the body weight gain was significantly increased, while the diarrhea incidence was significantly reduced in the EO group. In addition, EOs could modify the intestinal microbial composition of weaned piglets. The relative abundances of some beneficial bacterial species such as Bacilli, Lactobacillales, Streptococcaceae, and Veillonellaceae were significantly increased in the EO group. Metabolomics analysis indicated that protein biosynthesis, amino acid metabolism, and lipid metabolism were enriched in the EO group. And correlation analysis demonstrated that some gut bacterial genera were highly correlated with altered gut microbiota-related metabolites. Taken together, this study indicated that dietary EOs not only altered microbial composition and function but modulated the microbial metabolic profiles in the colon, which might help us understand EOs' beneficial effects on intestinal health of weaned piglets.