**3. Discussion**

*Essential Oils - Bioactive Compounds, New Perspectives and Applications*

**Compounds Molecular formula RIa RIb Oil**

α-Thujene C10H16 989 931 1.09 Sabinene C10H16 976 976 15.94 β-Pinene C10H16 980 980 2.01 α-Phellandrene C10H16 1006 1005 1.38 α-Terpinene C10H16 1019 1018 1.05 Limonene C10H16 1031 1031 5.19 1-8-Cineole C10H18O 1037 1033 3.04 γ-Terpinene C10H16 1060 1061 2.47 Terpinen-4-ol C10H18O 1178 1177 6.62 δ-Elemene C15H24 1335 1338 1.17 β-Caryophyllene C15H24 1421 1418 20.37 γ-elemene C15H24 1435 1433 1.04 α-humulene C15H24 1453 1454 1.17 Germacrene D C15H24 1481 1480 5.21 Bicyclogermacrene C15H24 1501 1488 7.02 Spathulenol C15H24O 1576 1576 11.09 Caryophyllene oxide C15H24O 1580 1581 3.18 Cubenol C15H26O 1641 1642 1.07 **Monoterpene hydrocarbons C10Hn 29.13 Sesquiterpene hydrocarbons C15Hn 35.98 Phenylpropanoids CnHnOn 25.00 Total identified (%) 90.11**

**144**

**Table 2.**

*a*

**Table 1.**

**2.3 Modulation of drugs**

*Retention indices from literature.*

*bacterial (ATCC) and multiresistant strains.*

and the treatments.

According to **Figure 3**, it was demonstrated that the essential oil of *M. suaveolens* does not have the capacity to modulate the antibiotics, gentamicin, imipinem, and norfloxacin, since there was no significant difference between the control group

*Minimal inhibitory concentration (μg/mL) of essential oil of* Mesosphaerum suaveolens *against conventional* 

*coli*

*Staphylococcus aureus*

**%**

**Strains** *Pseudomonas aeruginosa Escherichia* 

*Relative proportions of the essential oil constituents were expressed as percentages.*

*Retention indices experimental (based on homologous series of n-alkane C7-C30). <sup>b</sup>*

*Main constituents (>1%) of* Mesosphaerum suaveolens *essential oil.*

Strains standards (ATCC) ≥1024 ≥1024 64 Multi-resistant Strains ≥1024 ≥1024 256

Although the leaves of *M. suaveolens* are used in folk medicine for the treatment of diseases related to the gastrointestinal and respiratory tract [12], it has been demonstrated that the volatile terpenes of the species are not related to this action, since in the in the present study, this product did not present antibacterial action at concentrations of clinical relevance for two of the three strains used [23].

However, it is possible to observe that there is antibacterial action against the standard strains of *S. aureus* multiresistants. This can be explained by the mechanisms of action that some natural products have, such as the ability to disintegrate their cytoplasmic membranes, as well as destabilization of the proton motive force, electron flow, active transport and cellular content coagulation [24]. In addition, activity against *S. aureus* can be linked to the major compound of the study oil, β-caryophyllene, since this sesquiterpene exhibits antibacterial activity, especially against Gram-positive bacteria [25].

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.) [26]. 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 [8].

This variation in the essential oil explains why some works show the antibacterial action of the essential oil, as Tesch et al. [27], where the oil showed activity against *E. coli* ATCC 25922 (MIC 350 μL/mL), *Klebsiella pneumoniae* ATCC 23357 (MIC 300 μL/mL), *Salmonella* Typhi CDC57 (MIC 400 μL/mL). In this study, the natural product presented eucalyptol (C10H18O) and fenchone (C10H16O) as the main compounds.

In addition to antimicrobial activities, the products of plant origin can have a drug modulating action, and although *M. suaveolens* does not present such action, it is seen that in members of the Lamiaceae family, some species present such action. Among the species is *Origanum vulgare* L., where its essential oil has a modulating action of the tetracycline drug against bacterial strains of *S. aureus* IS-58, which had the TetK tetracycline efflux protein [28].
