ORIGANUM VULGARE ESSENTIAL OIL AND CARVACROL: NATURAL ALTERNATIVES AGAINST RESISTANT BACTERIA

: Bacteria that are resistant to several antibiotics are a serious One Health problem, as new alternatives for treatment do not appear at the same speed. Thus, the aim of this work was to carry out a survey of studies involving the activity of the essential oil of O. vulgare and its isolated compound carvacrol on antibiotic-resistant bacteria. To this end, a qualitative review of the literature was carried out in the PubMed database from 2015 to 2020. Both for the essential oil and for the isolated compound, the inhibitory action extends to strains often associated with difficult-to-treat infections such as oxacillin and vancomycin-resistant Staphylococcus aureus , β-lactamase-producing strains, carbapenemases, among others. The point that distinguishes the studies is the type of methodology used in the tests, with studies with carvacrol more directed towards mechanisms of molecular action and application in cells and animals, while those with oils are more preliminary. Although these substances have potential to control resistant bacteria, more research is needed to enable their use.


INTRODUCTION
There were many benefits of using antimicrobials, especially in the 20th century. However, in a short period of time, antibiotic-resistant bacteria emerged causing great concern with regard to human and animal welfare (FALEIRO; MIGUEL, 2013).
Over time, the excessive and indiscriminate use of these drugs resulted in the spread of these resistant bacteria and became a public health problem worldwide. In addition, antimicrobial resistance associated with the use of these antibiotics culminates in reduced effectiveness and likelihood of cure during the treatment of common bacterial diseases (CHENG et al., 2016).
Between 2012-2015, the microorganisms considered the main cause of infections in Brazilian hospitals were Klebsiella pneumoniae, coagulase-negative Staphylococcus (ECN), Staphylococcus aureus, Acinetobacter spp. and Pseudomonas aeruginosa. In addition, the rate of antibiotic resistance is high, and in the case of S. aureus, about 60% of the isolates were resistant to oxacillin (BRAZIL, 2016).
The biggest problem related to their presence is that the growing number of resistant strains is not accompanied by the research and development of new antimicrobials. In 2004, only 1.6% of the drugs under development by the world's largest pharmaceutical companies were antibiotics. This reduced production has several causes, including the typically very limited duration of treatments, which makes them less profitable than drugs for use in chronic diseases. Another reason is Characterized by a prominent odor, formed by the secondary metabolism of plants, essential oils are complex and volatile natural compounds extracted from various aromatic plants (BAKKALI et al., 2008). They are liquid, volatile, limpid and rarely colored products, liposoluble and soluble in organic solvents, with a density generally lower than that of water. They can be synthesized in various plant organs such as buds, flowers, leaves, stems, twigs, seeds, fruits, roots, wood or bark and are stored in secretory cells, cavities, channels, epidermal cells or glandular trichomes (BURT; REINDERS, 2003;BAKKALI et al., 2008). They can contain from twenty to sixty components in different concentrations and have mainly terpenes, terpenoids and other aromatic and aliphatic constituents characterized by low molecular weight. In nature, they play an important role in plant protection as antibacterial, antiviral, antifungal, insecticide and also against herbivores (BAKKALI et al., 2008).
Because of these activities present in essential oils and their compounds, these can be effective against multiresistant bacteria, but efforts should be made to improve the use of these promising substances for the treatment of infections (FALEIRO; MIGUEL, 2013).
An example of an essential oil known for its antimicrobial potential is the essential oil of Origanum vulgare, popularly known as oregano, which has several biological properties in addition to antimicrobial as an antioxidant, and antimutagenic, being mainly composed of phenolic components such as thymol and carvacrol has been widely studied against multiresistant microorganisms (GULLUCE et al., 2012;BEDOYA-SERNA et al., 2018).
Therefore, this review aims at the collection of scientific articles that relate the essential oil of Origanum vulgare and carvacrol as natural alternatives against resistant bacteria.

METHODOLOGY
A qualitative literature review was carried out (PEREIRA et al., 2018), where the research was based on articles available in the PubMed databases, from 2015 to 2020.
As inclusion criteria, articles related to essential oil and isolated compound used to combat bacteria were selected, including studies carried out in vitro, in vivo and ex vivo. Articles that were not available in full and review studies were excluded.

ANTIBACTERIAL ACTION OF ORIGANUM VULGARE
The literature has reported the inhibitory activity of the essential oil of Origanum vulgare  coli and Streptococcus typhimurium were tested against essential oils from various aromatic plants. Although studies reveal the potent antimicrobial activity of EOOV, its strong odor and taste may limit its application. In this sense, the use of nanoparticles can be an option for the applicability of this oil. Silver nanoparticles and EOOV showed bactericidal effects against Gram-positive and Gram-negative. When combined, the products exhibited additive or synergistic antibacterial effects for strains such as methicillin-resistant S. aureus (MRSA), E. coli producing extended-spectrum βlactamase (ESBL) and E. coli producing carbepenemase (SCANDORIEIRO et al., 2016).
Biofilm-producing strains also cause difficult-to-treat infections. Thus, EOOV was evaluated on the biofilm of Gram-positive bacteria and in association with antibiotics such as norfloxacin, oxacillin and gentamicin. The interaction of essential oils and norfloxacin was effective in destroying the biofilm, suggesting that the combination of antimicrobials from different sources may be promising therapeutic strategies (ROSATO et al., 2020).
In an attempt to discover new healing and treatment strategies, several researchers have been researching the different aspects of medicinal plants. Castronovo et al. (2020)  When evaluating the mechanisms of action against Salmonella Enteritidis, Barbosa et al. (2020) saw that sublethal concentrations of EOOV can lead to bacterial death acting at different levels: alteration of stress-related chaperones and proteins; alteration in cell communication and penetration into the bacterial cell acting on the synthesis of genetic material.
Another widely studied potential of EOOV is its role as a preservative in animal products, especially cheeses (KIM; MARSHALL; WEI, 1995;GULLUCE et al., 2012;GURDIAN et al., 2017;BEDOYA-SERNA et al., 2018;KHORSHIDIAN et al., 2018;SANTOS et al., 2022). Thus, studies on the use of EOOV in food preservation should be further developed, thus seeking alternatives for the use of this EO as a natural way of preserving food.

ANTIBACTERIAL ACTION OF CARVACROL
The antimicrobial activity is a result of the interaction of essential oil components, but, in some cases, compounds tested in isolation were also effective in controlling microorganisms. The activities of EOs of the genus Thymus and Origanum, for example, have been attributed to their phenolic components such as thymol and carvacrol (KIM; MARSHALL; WEI, 1995;BURT;REINDERS, 2003;BUSATTA et al., 2007).
Thymol and carvacrol are structurally similar components of EOOV. Generally, the antimicrobial activities of EO are difficult to correlate with a specific compound due to its complexity and variability; however, some researchers have stated that there is an association between the chemical composition of the most predominant compounds in the essential oil and the antimicrobial activity (EL ABED et al., 2014).
Carvacrol is responsible for increasing the permeability of the microbial cytoplasmic membrane, causing loss of cytoplasmic ATP. This action is due to its ability to interact with the cytoplasmic membrane, being able to dissolve in the lipid bilayer, aligning itself between the fatty acid chains (ARAUJO; LONGO, 2016). The presence of the hydroxyl group (OH) in the molecule of these phenolic compounds is an important agent against bacteria (ULTEE; BENNIK; MOEZELAAR, 2002).
Carvacrol is one of the major compounds in OEOV and in the essential oil of several other plants, so it is often evaluated in isolation for its potential against several pathogens. In this sense, strains of S. aureus were isolated from pasteurized milk and shrimp where antibiotic resistance was detected in 80% of them and about 34% were resistant to oxacillin and vancomycin (OVRSA).
Despite this, all were sensitive to carvacrol by the disk diffusion method and by the microdilution test, carvacrol had MIC values of 0.25 mg/mL and MBC of 0.5 mg/mL against OVRSA (VASCONCELOS et al., 2017).
Extended spectrum β-lactamase-producing bacteria (ESBL) encode the β-lactamase enzyme that confers resistance to most β-lactam antibiotics, generating a great constant challenge to antibiotic therapy. E. coli ESBL was inhibited by carvacrol with MIC of 450 μg/ml. This action was timedependent with a reduction of 2 log CFU/mL after sixtym minutes and complete inhibition after two hours. According to the authors, carvacrol has the ability to change the integrity of the membrane, resulting in the release of cellular content with potential application in bacteria causing urinary tract infection (KHAN et al., 2017).
Due to its antimicrobial activity, carvacrol was used in association with cinnamaldehyde to inhibit Acinetobacter baumannii. The mixture increased the expression of heat shock proteins, such as groES, groEL, dnaK, clpB and the catalase katE, and it was observed that carvacrol exerts a potent bactericidal activity, leading the bacteria to synthesize reactive oxygen species in response to the stress caused by it (MONTAGU et al., 2016).
In the current scenario, the interest in using natural antimicrobials in animal production has increased and compounds of essential oils have been evaluated to reduce colonization by pathogens.
Thus, Szott et al. (2020) added carvacrol to the feed (120 mg/kg of feed) of birds before slaughter age and observed a significant reduction in colonization by C. jejuni in the initial period of growth, opening space for studies to confirm the efficacy and commercial suitability and economical of the compost. Giovagnoni et al. (2020) analyzed the integrity of the Caco-2 cell monolayer and the findings indicate that carvacrol and thymol are candidate compounds for the control of Salmonella Typhimurium.
To promote the best antibacterial action, carvacrol was incorporated into nanoparticles and these were incorporated into dissolution microneedles in order to promote direct action on infected wounds. Effectiveness in releasing carvacrol at the wound site and a two-to four-fold increase in antimicrobial activity were observed in an ex vivo model (MIR et al., 2020). Otherwise, García-Salinas et al. (2018) evaluated the components of essential oils and observed action against E. coli, S. aureus and biofilm. An interesting fact of this research is that carvacrol, cinnamaldehyde and thymol presented lower cytotoxicity than chlorhexidine, usually used as a sanitizer.

CONCLUSIONS
The antibacterial activity of EOOV and carvacrol has been widely reported in the literature, mainly associated with the control of foodborne pathogens due to the plant's spice character.
However, when research is restricted to antibiotic-resistant bacteria, the number of works significantly reduces. Publications involving the EOOV show the use of more preliminary methodologies such as disk-diffusion and determination of the minimum inhibitory and bactericidal concentration. There is still a paucity of data on the mechanisms of antibacterial action. As for carvacrol, which integrates the composition of several essential oils, techniques aimed at antibacterial action are observed, as well as the molecular mechanisms of this activity, as well as tests applied to more complex models. The potential of EOOV and carvacrol as alternatives for the control of antibiotic-resistant bacteria alone or in association with other antimicrobial substances is undeniable.
There is an urgent need for therapeutic alternatives to control resistant microorganisms. Thus, substances extracted from spice plants, due to their low toxic potential, should be further studied, particularly on the molecular basis of their antibacterial mechanism of action. In this way, it will be possible to move towards its use in the promotion of single health.

ACKNOWLEDGEMENT
The Universidade Paranaense -UNIPAR and the National Council for Scientific and Technological Development and the Coordination for the Improvement of Higher Education Personnel for the granting of a scholarship and tuition fee for the Support Program for Postgraduate Studies in Private Education Institutions.