Main constituents (>1%) of
Mesosphaerum suaveolens (Lamiaceae) is a medicinal plant commonly used in Brazil for the treatment of diseases related to the digestive tract and respiratory diseases, so we hypothesized that the essential oil of this species may have antibacterial activity. Thus, we aimed to evaluate the in vitro antibacterial and modulatory activity of the essential oil of M. suaveolens as well as to characterize its chemical composition. The identification of the constituents was performed by gas chromatography-flame ionization detector (GC-FID) and the antibacterial and modulating activity by the plate microdilution method. We found the oil had sesquiterpene β-caryophyllene as the major component. This compound may account for the antibacterial activity against Staphylococcus aureus strains, since the essential oil had a MIC of 64 μg/mL for the standard strain and 256 μg/mL for the multiresistant strain, demonstrated that the oil does not exhibit drug modulating activity. Thus, M. suaveolens oil has bioactive compounds which can be used in the preparation of drugs.
- Hyptis suaveolens
- Escherichia coli
- Pseudomonas aeruginosa
- Staphylococcus aureus
Bacterial infections are major problems in medicine due to the indiscriminate use of antibiotics that eventually select resistant microorganisms, which in turn proliferate . Among the bacteria that cause infections stand out
It has been reported that the mechanisms of bacterial resistance include the efflux pumps, which expel the antibiotic, in addition, the bacteria are capable of altering the target of the antibiotic for mutation or enzymatic inactivation and alteration of the permeability of the bacterium to the drug . Thus, antibiotics alone cannot inhibit bacterial growth so that substances that modulate their effect are necessary in order to potentiate the action of the drug [6, 7].
These substances capable of modulating standard drugs can be found in plants, since these have constituents with antibacterial actions derived from their secondary metabolism, mainly the aromatic herbs, because their essential oils have diverse biological and pharmacological activities [8, 9]. Among the botanical families most rich in aromatic plants is Lamiaceae, which is well known for its representatives as sources of essential oils used in cooking, aromatherapy and medicine [10, 11]. Among the species of this family, the species
Thus, due to increasing bacterial resistance to drugs and the search for new bioactive sources, this research aims to evaluate the
2.1 Chemical composition of essential oil
The essential oil of
|Compounds||Molecular formula||RI a||RI b||Oil|
2.2 Minimal inhibitory concentration (MIC)
According to Table 2, the essential oil of
|Strains standards (ATCC)||≥1024||≥1024||64|
2.3 Modulation of drugs
According to Figure 3, it was demonstrated that the essential oil of
Although the leaves of
However, it is possible to observe that there is antibacterial action against the standard strains of
Thus, the oil has a source of β-caryophyllene, such sesquiterpene is found to be the majority compound; however, the oil of this species shows heterogeneity according to internal (genetic) and external factors (origin, mode of collection, collection period, etc.) . To avoid large variations in the chemical composition of the oil, the collections should be standardized, such as collection times, period of the year, as well as to identify if the individual is under herbivorous attack .
This variation in the essential oil explains why some works show the antibacterial action of the essential oil, as Tesch et al. , where the oil showed activity against
In addition to antimicrobial activities, the products of plant origin can have a drug modulating action, and although
4. Materials and methods
4.1 Collection of botanical material
Fresh leaves of
4.2 Extraction of essential oil
After drying, the leaves were packed in a volumetric flask containing 4 L of distilled water and subjected to constant boiling for 2 hours. Then the essential oil was collected and stored in an amber bottle under constant refrigeration until the conduction of the chemical analyzes and microbiological tests .
4.3 Phytochemical analysis of essential oil by gas chromatography (GC-FID)
For gas chromatography (GC), the Agilent Technologies 6890 N GC-FID system, equipped with DB-5 capillary column with the following specifications: 30 m of length, 0.32 mm and 0.50 μm of film thickness was used, which was connected to an FID detector. The temperature ramp consisted of: Initial temperature of 60°C for 1 min and was raised to 3° C/min until reaching 180°C .
4.4 Identification of the components
As for the identification, the terpenes were identified as to the of retention index (RI). In addition, they were compared with two spectral libraries, Nist and Wiley, and data in the literature .
4.5 Antibacterial activity
4.5.1 Bacterial strains, culture media and drugs
For the antibacterial tests, standard strains were used to determine minimum inhibitory concentration (MIC), being
|Urine culture||Cephalothin, cephalexin, cefadroxil, ceftriaxone, cefepime, ampicillin-sulbactam|
|Uroculture||Amikacin, imipenem, ciprofloxacin, levofloxacin, piperacillin-tazobactam, ceftazidime, meropenem, cefepime|
|Rectal swab culture||Cefadroxil, cephalexin, cephalothin, oxacillin, penicillin, ampicillin, amoxicillin, moxifloxacin, ciprofloxacin, levofloxacin, ampicillin-sulbactam, amoxilin/ac. Clavulanic, erythromycin, clarithromycin, azithromycin, clindamycin|
As for the culture medium for the antibacterial assays, Brain Heart Infusion (BHI) was prepared according to the measures recommended by the manufacturer. While for
4.5.2 Minimal inhibitory concentration (MIC)
It was followed the methodology employed in the work Bezerra et al.  for the determination of the Minimum Inhibitory Concentration (MIC). In this study, concentrations ranging from 1 to 1024 μg/mL of the essential oil of
4.5.3 Effect modulator of antibiotics
To assess the modulating effect of essential oil, sub-inhibitory concentrations (MIC/8) of the product against multidrug-resistant bacteria were used. For that, concentrations of standard antibiotics (1–1024 μg/mL) were added to microdilution plates containing BHI (10%) and bacteria inoculum, as well as volatile
4.6 Statistical analysis
The results were analyzed in the GraphPad Prism program, version 6, in which the data were analyzed by Anova One-way and followed by post hoc Tukey test and were considered significant when
The essential oil of
The authors thank the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), and the Fundação Cearense de Apoio ao Desenvolvimento Científico e Tecnológico (FUNCAP).
Conflict of interest
The authors declare no conflict of interest.
This research received no external funding.