Carvacrol and Eugenol - detailed description of the substances

Carvacrol (CV) is a phenolic monoterpenoid found in the essential oils of plants such as oregano (Origanum vulgare), thyme (Thymus vulgaris), lepidium flavum (Lepidium flavum), wild bergamot (Citrus aurantium bergamia) and others. It exhibits a wide range of bioactivities that can be valuable for clinical applications, including antimicrobial, antioxidant and anticancer properties. The antimicrobial activity is attributed to the free hydroxyl group, hydrophobic nature and phenolic structure of carvacrol. Recent studies on carvacrol have shown a significant potential agent against food-borne pathogens, especially Escherichia coli, Salmonella and Bacillus cereus. In addition, carvacrol exhibits significant antioxidant activity and has been successfully used, often in combination with thymol, as a phyto-additive to the diet to increase antioxidant status.

On the other hand, eugenol, also known as C10H12O2 or CH3C6H3, is a volatile phenolic compound. It is found in clove essential oil extracted from the buds and leaves of Eugenia caryophyllata trees. Eugenol is the main component (70-90%) of clove oil and contributes to its characteristic aroma. Traditionally, clove oil, which contains eugenol, has been used in traditional Chinese medicine for its antibacterial, antiseptic and antispasmodic properties.

Carvacrol and eugenol against Candida species

Carvacrol and eugenol are being widely studied for their potential as antifungal and antimicrobial agents. In particular, they are being tested against Candida species, especially in animal experimental models.

In a study focused on oral candidiasis, both carvacrol and eugenol showed significant antifungal activity by significantly reducing the number of Candida colony-forming units (CFUs) in the oral cavity over a treatment period of eight days. Microbiological and histopathological evaluations showed that both compounds effectively inhibited fungal growth. Carvacrol was particularly effective, completely preventing the colonization of filamentous fungi, while eugenol allowed only a small local presence of filamentous fungi. These results support the potential use of carvacrol and eugenol as alternative therapeutic options for oral candidiasis, acting comparably to the standard antifungal agent, nystatin [1].

In another study on vaginal candidiasis, both carvacrol and eugenol showed beneficial prophylactic and therapeutic effects against Candida albicans. Prophylactically, carvacrol effectively eliminated the presence of vaginal fungi, while eugenol achieved a significant reduction in Candida colonies after treatment. In particular, histological evaluations confirmed that treated rats showed no Candida in the vaginal lumen compared to control groups. These findings underscore the efficacy of carvacrol and eugenol as natural antifungal agents, suggesting their potential in the prevention and treatment of vaginal candidiasis [2].

In addition, a clinical study was conducted to evaluate the antifungal efficacy and potential synergistic effect of five essential oil components - cinnamaldehyde, α-pinene, limonene, eucalyptol and eugenol - against various Candida strains isolated from clinical vaginal samples. The results showed that cinnamaldehyde and eugenol exhibited the most significant antifungal activity, inhibiting all tested strains and showing a strong additive effect. Eugenol showed an average zone of inhibition (IZ) of 35.2 mm and eliminated fungal cells within 1 hour. These findings indicate that eugenol provides significant potential as a safe, natural treatment for candidiasis [3].

In addition, another study examined the combination of eugenol with lower, less toxic doses of amphotericin B (AmpB) to enhance antifungal activity and minimize toxicity against Candida albicans. The results showed that the combination of eugenol and AmpB resulted in significantly greater activity against Candida compared to treatment with either agent alone. The combination led to fungal cell death induced by reactive oxygen species (ROS) and mitochondrial hyperpolarization. Eugenol also appears to inhibit calcium channels and increase AmpB retention in fungal cells, leading to significant cell damage. These findings support the potential use of eugenol in combination with amphotericin B to effectively treat Candida infections while reducing the need for higher, more toxic doses of antifungal drugs [4].

Moreover, a clinical study on candidiasis evaluated the antifungal properties of clove essential oil (CEO) and eugenol (EUG). The researcher isolated Candida spp. from the mouths of patients with hematologic malignancies. The study showed that CEO and EUG were effective against all Candida strains tested, with minimum inhibitory concentrations (MICs) ranging from 0.25-2 mg / ml. Both natural products showed the ability to bind to ergosterol in the yeast cell membrane. In addition, interactions between CEO, EUG and various antifungal drugs - cetylpyridinium chloride,
chlorhexidine, silver nitrate and triclosan - showed synergistic or additive effects, with the exception of nystatin. These results highlight CEO and EUG as promising phytopharmaceuticals for topical use in the treatment of superficial candidiasis [5].

In addition, another study focused on the effect of eugenol on biofilm formation by Candida species (Candida dubliniensis and Candida tropicalis) in HIV-infected patients. Biofilm formation greatly complicates infections, often leading to resistance to antimicrobials and host defense mechanisms. The results showed that eugenol effectively inhibited biofilm formation and metabolic activity in biofilms after 24 hours of treatment. In addition, eugenol exposure decreased the hydrophobicity of planktonic cells and significantly reduced their adhesion to HEp-2 cells and polystyrene surfaces. These findings confirm eugenol's potent antifungal properties against non-albicans Candida species, highlighting its dual efficacy in inhibiting both planktonic cell growth and biofilm formation on various surfaces [6]. In addition, the study evaluated the in vitro efficacy of eugenol against mixed biofilms of Candida albicans and Streptococcus mutans. Eugenol alone and in combination with antimicrobial drugs was effective against biofilms, showing strong synergy, especially with fluconazole and azithromycin. Eugenol significantly reduced the number of C. albicans cells in both single and mixed biofilms. At a concentration of 800 μg/ml, microscopic examination confirmed the removal of biofilm cells from glass surfaces. A time-dependent kill assay showed a dose-dependent eradication effect of eugenol on pre-formed biofilm cells. Importantly, eugenol showed strong synergy with fluconazole against CAJ-12 biofilms and with azithromycin against mixed biofilms, indicating strong antimicrobial interactions. These findings suggest that eugenol, especially in combination with fluconazole or azithromycin, is highly effective in controlling oral infections by targeting C. albicans and S. mutans biofilms [7].

The scientific study investigated the mechanisms of action of the main phenolic components of oregano and clove essential oils - carvacrol and eugenol - against Candida species. Their effects were also evaluated for therapeutic efficacy in the treatment of experimental oral candidiasis caused by Candida albicans in immunosuppressed rats. Carvacrol and eugenol had fungicidal effects on exponentially growing C. albicans. Interestingly, this fungicidal effect was accompanied by the release of absorbing substances at 280 nm. In an immunosuppressed rat model of oral candidiasis, treatment with carvacrol or eugenol significantly reduced the number of colonies collected from the mouth of rats treated for eight consecutive days compared to untreated rats
controls. Similar results were obtained with nystatin used as a reference treatment. In vitro results indicated that both carvacrol and eugenol exerted antiparasitic effects by damaging cellular integrity [8].

In addition, another study evaluated the efficacy of eugenol and fluconazole in the treatment of Candida keratitis using an experimental model. The results showed that the minimum inhibitory concentrations (MICs) of eugenol and fluconazole against C. albicans were 2 mg/ml and >0.4 mg/ml, respectively. The study showed that at least 75% eyes treated with eugenol fully recovered from keratitis, and the remaining 25% showed significant improvement compared to the control group. The results indicate that eugenol is a natural, safe and effective antifungal drug for the treatment of fungal keratitis, effective whether treatment was started immediately or four days after the induction of keratitis [9]. Moreover, the study evaluated three potent eugenol tosylate congeners (ETC-5, ETC-6, ETC-7) for their effects on key virulence factors of Candida albicans. ETCs significantly reduced C. albicans adherence, completely inhibited morphogenesis at the minimum inhibitory concentration (MIC) and significantly reduced biofilm formation. They also inhibited enzymatic activity and down-regulated virulence-related genes. These findings suggest that these novel ETCs effectively target and inhibit major virulence factors in C. albicans, preventing its transition from a commensal to a pathogenic state [10].

Another study of eugenol's antifungal potential showed that at a concentration of 1.0% v/v, eugenol effectively inhibited the growth of C. albicans and was fungicidal. It caused leakage of cellular contents and increased cell permeability. Microscopic analysis revealed disruption of the cell wall structure of C. albicans under the influence of eugenol. This suggests that eugenol disrupts the integrity and morphology of the cell wall, ultimately inhibiting fungal growth [11]. Moreover, another study showed that eugenol-derived imidazole 13 exhibited remarkable potency against Candida albicans and minimal toxicity. The results also revealed that the derivative compounds interfered with fungal ergosterol biosynthesis, a key process in fungal survival, and interacted with a key enzyme involved in this pathway. These findings underscore the potential of derivative compounds as candidates for the development of new antifungal therapies [12].

A study of mechanisms against fungal infections has shown that eugenol binds to the Candida cell membrane, interfering with ergosterol biosynthesis and causing cell wall and membrane damage. It also inhibits the formation of nucleated tubules, reduces oxidative stress in fungal cells and increases cell membrane permeability. In addition, eugenol inhibits fungal adhesion to surfaces, prevents biofilm formation and interferes with the
biofilm formation. These actions make eugenol a potent agent against candidiasis, especially for mucocutaneous forms such as oral and vulvar and vaginal infections. However, further studies, including clinical trials and molecular analyses, are needed to fully understand its therapeutic potential and develop new eugenol-based antifungal agents [13].

Moreover, one study examined the antifungal properties of eugenol and its interaction with the antifungal drug nystatin against Candida albicans. The results indicated that eugenol has antifungal properties against C. albicans [14]. In addition, a study on carvacrol revealed its significant antifungal activity against Candida species, including C. albicans and Nakaseomyces glabratus. Carvacrol was found to disrupt the integrity of fungal vacuoles, leading to impairment of vacuolar functions necessary for fungal growth and morphogenesis. This disruption results in reduced filament formation and defective fungal structures. These findings point to the inclusion of carvacrol in antifungal treatment strategies, especially as an alternative in the fight against increasing antifungal resistance [15].

In addition, the combination of the antifungal drug voriconazole with carvacrol against various Candida species was tested in a scientific study. Carvacrol showed significant antifungal activity with MICs averaging 66.87 μg / ml for C. albicans, 75 μg / ml for C. glabrata and 95 μg / ml for C. krusei. Voriconazole had different levels of efficacy, and the combination of carvacrol and voriconazole showed synergistic effects [16]. Another study evaluated the antifungal efficacy of carvacrol against C. auris using a microdilution method to determine MICs, which ranged from 125 to 500 μg/ml. Carvacrol was found to induce oxidative stress in C. auris, as evidenced by a significant increase in antioxidant enzyme activity and lipid peroxidation levels. This oxidative stress is a potential mechanism for its antifungal activity [17]. Additionally, the study examined the potential of carvacrol as an effective antifungal agent against Candida albicans. The results showed that carvacrol treatment elevated oxidative stress, disrupted mitochondrial function and increased calcium levels, all of which are indicative of cellular stress and apoptosis. Importantly, the study showed that carvacrol induces apoptosis in C. albicans through activation of calcineurin, a key signaling pathway. These findings confirm that carvacrol effectively controls C. albicans through a variety of mechanisms, including direct antifungal activity and immune modulation [18].

Another study also examined the antifungal mechanisms of thymol and carvacrol against Candida albicans. The results revealed that exposure to thymol and carvacrol induced oxidative stress and weakened the antioxidant defense systems of C. albicans, leading to membrane damage and
toxic radical cascade mediated by lipid peroxidation. The results suggest that carvacrol threatens the viability of C. albicans by inducing oxidative stress and interfering with cellular antioxidant mechanisms [19].

What's more, a scientific study examined the potential of carvacrol in the treatment of oral candidiasis. Samples were taken from dental clinic patients, particularly denture wearers. Candida fungi were cultured to evaluate their sensitivity to carvacrol and nystatin. Carvacrol showed significant antifungal activity against all Candida species tested, with an average minimum inhibitory concentration (MIC) of 24.96 μg/ml and a minimum fungicidal concentration (MFC) of 23.48 μg/ml. Compared to nystatin, carvacrol showed lower MICs, and when combined with nystatin, it increased antifungal efficacy. These results suggest that carvacrol may be an effective treatment for oral candidiasis, offering a promising alternative to antifungal therapy [20]. Another study evaluated the combined effects of carvacrol and thymol on the growth of single and mixed biofilms of Candida albicans and Staphylococcus epidermidis. The combination of carvacrol and thymol showed strong microbicidal activity, effectively eliminating highly tolerant spore cells in biofilms. This significantly reduced biofilm viability and structural integrity, suggesting a reduced risk of resistance development [21]. Interestingly, the study examined the potential of incorporating eugenol, the main ingredient in clove oil, into a dental paste called Orabase. The researchers aimed to evaluate the antifungal potential of eugenol in a formulation suitable for oral use. The results showed that Orabase formulations containing eugenol exhibited significant antifungal activity with optimal physical properties for oral use. The formulation provided a controlled and gradual release of eugenol, effectively combating the fungal infection, and exhibited strong adhesive properties, providing prolonged contact with the affected areas of the oral cavity. These findings suggest that the inclusion of eugenol in Orabase is a viable and innovative approach to improving the treatment of oral candidiasis [22].

Carvacrol and eugenol against Escherichia coli

The research study examined the use of carvacrol and eugenol as potential treatments for urinary tract infections (UTIs) caused by multidrug-resistant strains of E. coli, commonly found in hospitals and community settings. These bacteria often communicate and organize their harmful activities through a process known as quorum sensing (QS). By disrupting QS, carvacrol and eugenol can help treat infections that would otherwise
So far, they are resistant to many antibiotics.

The study showed that a significant number of E. coli isolates from urine samples of patients in Egypt were resistant to multiple antibiotics. In particular, 94% of the 67 isolates tested showed multi-drug resistance, and nearly half of them were identified as uropathogenic E. coli (UPEC), which are specifically associated with URI. Eugenol proved particularly effective, reducing biofilm formation by more than 50% under typical body temperature conditions. Moreover, carvacrol and eugenol also significantly reduced the activity of QS genes in bacteria, suggesting that they may impair the bacteria's ability to coordinate attacks. When carvacrol and eugenol were combined with conventional antibiotics, they significantly increased the effectiveness of antibiotics, showing potential as a complementary treatment to help overcome antibiotic resistance [23].

Another study focused specifically on the antimicrobial potential of carvacrol against E. coli bacteria that produce extended-spectrum β-lactamases (ESBLs). Carvacrol showed significant antimicrobial activity, completely inhibiting the growth of E. coli within 2 hours of exposure. It induced reactive oxygen species production, bacterial membrane depolarization and cell death. Even at subinhibitory concentrations, carvacrol reduced the motility and invasion capacity of E. coli, indicating its potential as an alternative treatment option [24].
What's more, another study tested whether combining citrus fruit extracts (CFEs), such as lime, lemon and calamansi, with essential oil components (EOCs), particularly carvacrol and thymol, could increase their antimicrobial efficacy. The study tested the effects of these extracts and essential oils both separately and together on various bacteria, including E. coli O157:H7, Salmonella Typhimurium and Listeria monocytogenes at room temperature. Used separately, neither citrus extracts (at concentrations below 20%) nor essential oils (at 2.0 mM or 0.032%) were able to effectively kill the bacteria. However, when combined, these agents showed significant synergy, completely eliminating all bacteria tested. The results suggest that combining citrus fruit extracts with essential oils such as carvacrol and thymol can significantly improve their antimicrobial properties [25]. In addition, the study examined the effects of sublethal exposure to essential oils (EOs) such as thymol (Thy), carvacrol (Car) and trans-cinnamaldehyde (TC) on the virulence characteristics of Escherichia coli O157:H7, a harmful bacterium often associated with foodborne illness. The results showed that sublethal doses of Thy, Car and TC significantly reduced the motility, biofilm formation and efflux pump activity of E. coli O157: H7. These effects were found to be reversible - meaning that they returned to normal levels after removal of EO exposure - demonstrating that these conditions did not induce permanent changes in these
virulence characteristics. Importantly, the study also showed that there was no increase in antibiotic resistance or significant changes in the bacteria's ability to adhere to or invade human cells [26].

Antifungal potential of carvacrol and eugenol

A scientific study examined the potential of eugenol against the fungus Trichophyton rubrum, a common cause of chronic dermatophytosis and often resistant to antifungal drugs. The results showed that eugenol had an MIC of 256 μg/ml, effectively inhibiting the growth of 50% strains of T. rubrum tested. The study also observed a significant reduction in mycelial growth (the vegetative part of the fungus) and conidia germination (the process of germinating fungal spores), indicating a strong antifungal effect. Moreover, eugenol caused noticeable morphological changes in the fungus, including the formation of broad, short and twisted stipules (the long filamentous branches of the fungus), along with a decrease in conidiogenesis (the formation of conidia or asexual spores). These antifungal effects are thought to be due to eugenol's action on the fungus' cell wall and cell membrane, in particular its ability to inhibit ergosterol biosynthesis. Ergosterol is a key component of fungal cell membranes, essential for their integrity and functionality. By interfering with this process, eugenol disrupts the cell structure and growth mechanisms of the fungus [27]. The findings underscore eugenol's potential as a potent antifungal agent, suggesting that it may be a promising alternative for treating infections caused by T. rubrum, especially for those strains that are resistant to existing antifungal drugs.

In another study examining eugenol's antifungal activity, researchers tested its activity against various fungi, including species of aspergilli (Aspergillus Niger, Aspergillus terreus and Emericella nidulans), penicilli (Penicillium expansum, Penicillium glabrum and Penicillium italicum) and fusaria (Fusarium oxysporum and Fusarium avenaceum). The study showed that eugenol's ability to inhibit fungal growth varied significantly among different strains and species. A concentration of 100 mg/liter was identified as the key threshold for growth inhibition of P. expansum, P. glabrum, P. italicum, A. niger and E. nidulans, above which eugenol's effect was mainly fungistatic, meaning that it could prevent further growth but not kill the fungi. In the case of A. terreus and F. avenaceum, growth inhibition was achieved at a slightly higher concentration of 140 mg/liter. It is worth noting that the growth of F. oxysporum was completely stopped at a concentration of 150 mg/litr, indicating a particularly strong antifungal effect against this species [28].

Another study in mice showed that eugenol was effective in reducing the severity of keratitis. It achieved
this by reducing inflammatory cell infiltration, decreasing the expression of pro-inflammatory cytokines and lowering the fungal load in the eye. Additionally, in human corneal epithelial cells, eugenol was found to reduce the production of pro-inflammatory cytokines. Its anti-inflammatory properties were attributed to activation of the Nrf2/HO-1 signaling pathway, which plays an important role in cellular defense mechanisms against stress and injury. Moreover, eugenol showed strong antifungal activity against Aspergillus fumigatus. It inhibited fungal growth, prevented the fungus from adhering to host cells and damaged the structural integrity of fungal biofilms. This antifungal activity is thought to be due to eugenol's ability to disrupt the fungus' cell membrane and interfere with the synthesis of ergosterol, an essential component of the fungus' cell wall. These findings suggest that eugenol may be an effective therapeutic option for treating fungal keratitis, offering dual benefits by reducing inflammation and combating fungal infection [30].

Human study on eugenol against vaginal candidiasis

Eugenol was evaluated for efficacy in the treatment of vaginal candidiasis (VC) in a comprehensive study along with thymol in a vaginal formulation. The study included 459 patients from 23 Italian gynecological departments who were randomly assigned to different treatments based on their diagnosis of bacterial vaginitis (BV) or vaginal candidiasis. For those diagnosed with BV, the treatment options compared were a daily rinse containing thymol and eugenol for a week and standard treatment with vaginal suppositories containing econazole, applied every night for three days. The results showed that thymol and eugenol applied vaginally were as effective as econazole in reducing symptoms of vaginal candidiasis. The study underscores the potential of eugenol as an effective antifungal agent capable of reducing dependence on conventional antifungal drugs. These findings are important because they suggest that natural remedies such as eugenol may be as effective as traditional treatments for fungal infections such as vaginal candidiasis [29].

Antiviral potential of carvacrol and eugenol

In a detailed study of carvacrol's antiviral properties, the researchers focused on its efficacy against herpes simplex virus (HSV) in vitro. The study used the BSC-1 cell model to examine how carvacrol can combat HSV, specifically analyzing its ability to prevent infection, treating the
infected cells and direct inactivation of the virus. The study showed that carvacrol was effective in all three scenarios, with half-maximal effective concentrations (EC50) for HSV-2-infected cells of 0.43, 0.19 and 0.51 mmol / l, respectively. Carvacrol was particularly effective in reducing transcription and protein levels of several key viral factors and cytokines that are typically elevated during HSV-2 infection. The study showed that HSV-2 infection often leads to a reduction in intracellular protein ubiquitination, a critical process for cellular health that carvacrol effectively reversed. This suggests that carvacrol not only prevents viral replication, but also helps restore cellular functions disrupted by the virus. Overall, the findings reveal that carvacrol has significant antiviral properties, particularly against HSV-2, by inhibiting virus growth and modulating the host cell's immune response [31].

What's more, another study examined the antiviral effects of oregano oil, specifically its components carvacrol and thymol, against HIV and SIV (simian immunodeficiency virus). In contrast to their limited efficacy against other viruses, such as hepatitis C, Zika and influenza, carvacrol and thymol effectively blocked the fusion of the HIV virus with target cells, an important step in the virus' life cycle. Studies have shown that carvacrol works by removing cholesterol from the HIV-1 envelope membrane, thereby interfering with the virus' ability to enter and infect host cells. This disruption is important because fusion of the virus with the host cell is a key mechanism of HIV spread. The study identified specific changes (mutations) in the viral fusion protein gp41 as a mechanism for the development of resistance. Further studies of the structure-activity relationship between carvacrol and thymol led to the identification of specific molecular motifs key to their antiviral activity and the development of new, more potent analogs [32].

In addition, the efficacy of carvacrol against influenza A was tested using an extract of Mosla chinensis Maxim, a plant traditionally used in Chinese medicine to treat symptoms associated with cold and flu. The study used mouse models infected with influenza A virus to evaluate the therapeutic potential of carvacrol. The results were promising, showing that treatment with carvacrol significantly reduced lung tissue damage and attenuated the immune system response. It achieved these effects by adjusting the balance of T helper cell types and lowering key pathways involved in viral recognition and inflammation. These findings support the traditional use of carvacrol-rich plants in the treatment of respiratory infections and suggest its
usefulness as an alternative or complementary treatment for influenza [33].

In addition, one study examined the therapeutic effect of carvacrol on nasal septum perforations in rabbits. The study involved twenty-one male New Zealand rabbits, divided into three groups, with perforated nasal septa and then treated with various interventions. After two weeks, the results showed a significantly higher perforation closure rate in the group treated with carvacrol compared to the others. In particular, histopathological analysis showed increased cartilage regeneration and increased connective tissue density in this group. The study concluded that topical application of carvacrol could significantly improve healing of nasal septal perforations, potentially reducing the need for surgical intervention [34].

Eugenol for allergic rhinitis

The study evaluated the effect of methyl eugenol on aquaporin 5 (AQP5) expression in the nasal mucosa of rats suffering from allergic rhinitis. A total of 128 Wistar rats were divided into several groups, including normal control, allergic rhinitis model control, budesonide positive control and four different methyleugenol dosage groups. The results showed that methyl eugenol treatment led to a significant increase in AQP5 expression compared to the allergic rhinitis model control, with effects comparable to budesonide after two weeks. The study suggests that methyl eugenol may be effective in reducing nasal mucosal edema and glandular secretion, indicating a potential new treatment for allergic rhinitis symptoms [35].

Eugenol against herpes simplex viruses HSV-1 and HSV-2.

Eugenol was also tested against herpes simplex viruses HSV-1 and HSV-2. In vitro studies showed that eugenol effectively blocked replication of these viruses. The specific doses of eugenol needed to inhibit 50% virus activity (IC50) were found to be 25.6 micrograms per milliliter for HSV-1 and 16.2 micrograms per milliliter for HSV-2. Importantly, these concentrations showed no toxicity in cytotoxicity tests conducted up to a maximum dose of 250 micrograms per milliliter. Moreover, when eugenol was combined with acyclovir, a commonly used antiviral drug, the mixture showed synergistic effects, meaning that the combination was more effective in inhibiting herpes viruses than either compound alone. In addition to its in vitro efficacy, eugenol also showed potential in vivo benefits: when applied topically, it delayed the onset of keratitis, an eye disease often caused by herpes virus infections, in a mouse model.
These findings underscore the potential of eugenol as a therapeutic option to treat or cure herpes virus infections [36].

Carvacrol and eugenol against bacterial infections

Various studies have demonstrated the antibacterial properties of carvacrol and eugenol in animal and laboratory models. One study highlighted the synergistic effect of eugenol and the probiotic Lactobacillus plantarum ZS2058 (ZS2058) against Salmonella infections in mice. Eugenol showed selective antimicrobial activity that was more potent against Salmonella than ZS2058 alone during in vitro tests. The combination treatment significantly improved the survival rates of infected mice from 60% to 80%, a significant improvement over the effect of each agent alone. The combination proved to be twice as effective as ZS2058 alone and six times more effective than eugenol alone in preventing Salmonella infection [37].

In addition, the researchers evaluated the antimicrobial efficacy of trans-cinnamaldehyde (TC) and eugenol (EG) against Acinetobacter baumannii. The results showed that both TC and EG significantly reduced the adhesion of A. baumannii to human keratinocytes (HEK001) by about 2 to 3 log10 CFU/ml, a significant reduction indicating strong antimicrobial activity. Moreover, the compounds also reduced the invasion of these cells by a similar amount. When biofilm formation, which is a critical factor in the persistence and resistance of infections, was tested, both TC and EG showed a reduction in biofilm mass of about 1.5 to 2 log10 CFU/mL after 24 hours and 2 to 3.5 log10 CFU/mL after 48 hours compared to controls [38].

Another study also evaluated the antitubercular activity of eugenol (EUG) and its derivatives against Mycobacterium tuberculosis (Mtb) and nontuberculous mycobacteria (NTM), as well as their interactions with traditional antituberculosis drugs. Eugenol and its derivatives not only inhibited the growth of Mtb and non-tuberculous mycobacteria (NTM), but also showed synergistic effects with established anti-tuberculosis drugs such as rifampicin, isoniazid, ethambutol and pyrazinamide. The study specifically highlighted that these combinations were more effective than the drugs alone, especially against multidrug-resistant Mtb strains [39].

In addition, one study examined the use of carvacrol as a therapeutic agent against Campylobacter jejuni. They used a clinical mouse model to evaluate its effectiveness in treating campylobacteriosis, an infection caused by a common zoonotic pathogen. The results showed that by the sixth day after infection, mice treated with carvacrol
showed a significant reduction in pathogen burden - two log orders lower than control mice - and exhibited milder disease symptoms compared to placebo-treated mice. The therapeutic benefits of carvacrol were not limited to the gastrointestinal tract, as evidenced by reduced intestinal apoptosis, reduced pro-inflammatory immune response, increased colonic epithelial cell proliferation and lower systemic inflammatory markers such as IFN-γ, TNF, MCP-1 and IL-6. In addition, carvacrol effectively prevented the spread of C. jejuni to extraintestinal sites such as the liver, kidneys and lungs. These findings underscore the potential of carvacrol as a promising treatment for campylobacteriosis [40].

Interestingly, the study looked at improving the treatment of chronic wound infections using carvacrol-containing nanoparticles. The results showed that the release of carvacrol from the nanoparticles was significantly increased in the presence of bacteria, suggesting an effective on-demand delivery mechanism. Encapsulation of carvacrol in PCL nanoparticles also increased its antimicrobial activity by 2-4 times. Dermatokinetic studies showed that micro-needles containing PCL carvacrol nanoparticles significantly improved carvacrol retention in the skin to 83.8% after 24 hours, compared to only 7.3% for micro-needles containing free carvacrol. This innovative delivery system has the potential to improve the treatment of infected chronic wounds, overcoming the limitations of traditional treatments and providing a targeted approach to fighting infection in necrotic tissue [41].

In addition, the researchers evaluated the antimicrobial potential of carvacrol against carbapenem-resistant Klebsiella pneumoniae (CRKP). They focused on this pathogen due to its resistance to carbapenem antibiotics and polymyxin. The results showed that carvacrol was able to eliminate all the bacterial cells tested within four hours of in vitro exposure. In addition, the efficacy of carvacrol was also tested in vivo using a mouse model infected with Klebsiella pneumoniae carbapenemase producers (KPC). The results of the in vivo test showed that treatment with carvacrol significantly improved survival rates, reduced the bacterial load in the peritoneal lavage and had a positive effect on immune response markers such as white blood cell count and platelet levels. These results suggest that carvacrol may be an effective alternative for treating infections caused by CRKP, a pathogen known to be extremely resistant to many drugs[42].

Another study looked at carvacrol as a preventive treatment for campylobacteriosis, a gastrointestinal disease caused by Campylobacter jejuni, which is known to lead to post-infection autoimmune complications. The study showed that although carvacrol prophylaxis did not change the burden of gastrointestinal pathogens or affect the composition of the human commensal intestinal microflora, significantly improved clinical outcomes. In particular, treatment with carvacrol decreased apoptosis in colonic epithelial cells and reduced pro-inflammatory immune responses in both the gut and extraintestinal organs such as the liver and spleen. These findings suggest that carvacrol may be a valuable non-antibiotic prophylactic agent to alleviate symptoms of acute campylobacteriosis and potentially reduce the risk of subsequent autoimmune complications [43].

The researchers also worked on the efficacy of eugenol against methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-sensitive S. aureus (MSSA). The study used both in vitro and in vivo models. The results showed that eugenol significantly inhibited the growth of MRSA and MSSA biofilms in a concentration-dependent manner, effectively eliminating previously established biofilms at concentrations at or above the minimum inhibitory concentration (MIC). In vivo, eugenol at concentrations below the MIC reduced S. aureus colonization in the rat middle ear by 88%, disrupted cell membranes, led to leakage of bacterial contents and downregulated genes associated with biofilm and enterotoxin production. Importantly, a significant synergy was observed when eugenol was combined with carvacrol, increasing the elimination of established biofilms [44].

Carvacrol for bacterial vaginitis (BV)

A study was also conducted on the antimicrobial properties of carvacrol against Gardnerella spp. which are important in the pathology of bacterial vaginitis (BV). The study evaluated the single and combined effects of carvacrol, ρ-cymene and linalool on both planktonic cultures and biofilms of Gardnerella spp. The results showed that carvacrol had a strong synergistic effect in inhibiting planktonic cultures. At the sub-MIC level, carvacrol and linalool were particularly effective against biofilm cells. These compounds were also shown to effectively disrupt biofilm integrity, preventing regeneration and regrowth after exposure to fresh medium. Importantly, the essential oils and their constituents showed no cytotoxic effects in a reconstituted model of human vaginal epithelium. These results suggest that carvacrol, along with ρ-cymene and linalool, may be a viable alternative to traditional antibiotics in the treatment of BV [45].

Eugenol against leishmaniasis

Researchers have investigated the therapeutic role of eugenol oleate in visceral leishmaniasis (VL), a serious disease found mainly in tropical and subtropical areas. They used a mouse model to study how well eugenol oleate can remove the parasite
causing the disease. The results were promising: it removed about 86.5% of parasites in the liver and 84.1% in the spleen. The study showed that eugenol oleate helps the immune system better fight the disease by shifting the immune response toward a Th1 profile, which is more effective against such infections. This happens by activating certain pathways in immune cells that lead to the production of important molecules (such as IL-12 and IFN-γ) that help kill parasites. These findings suggest that eugenol oleate may be a useful treatment for VL [46]. Moreover, another study looked at a eugenol derivative for the treatment of cutaneous leishmaniasis (CL), a type of leishmaniasis that attacks the skin and is a major health problem in more than 98 countries. There are currently no vaccines for CL, and treatment often has serious side effects. The eugenol derivative showed good potential in laboratory tests, effectively killing the parasites and showing less toxicity to human cells compared to some existing drugs. It was particularly effective when administered orally to infected mice, reducing both visible symptoms and parasite numbers, similar to some treatments injected into lesions [47].

Eugenol for dental health

Interestingly, the study compared the efficacy of eugenol-based toothpaste and 0.2% chlorhexidine gel in preventing alveolar osteitis, a painful condition that can occur after the extraction of third molars (wisdom teeth). The study involved 270 patients undergoing wisdom teeth extraction. These patients were divided into three groups: one treated with chlorhexidine gel, another with eugenol-based paste, and a control group that received no postoperative treatment. At seven days after surgery, the incidence of alveolar osteitis was significantly lower in the eugenol group, with no reported cases, compared to 2% in the chlorhexidine group and 10% in the control group. The study concluded that eugenol-based paste was more effective than chlorhexidine gel in preventing alveolar osteitis, and provided better results in terms of reducing postoperative pain, inflammation and promoting wound healing [48].

Another study focused on the development and evaluation of eugenol-containing nanocapsules for the treatment of periodontal infections. The in vitro release of eugenol from these nanocapsules showed a controlled, biphasic pattern, suggesting an effective release mechanism. In addition, cell viability tests showed that the nanocapsules were non-toxic. In vivo tests on a rat model of induced periodontitis showed that eugenol nanocapsules effectively
prevented bone resorption and improved gingival epithelial tissue compared to the control group. These findings show that eugenol-containing nanocapsules may be a promising option to enhance the therapeutic effects of eugenol in the treatment of periodontal infection [49].

Eugenol for contact dermatitis

In addition, one study examined the potential of eugenol, encapsulated in polymeric nanocarriers, to treat contact dermatitis, a common inflammatory skin condition. Although eugenol has beneficial anti-inflammatory and antioxidant properties, its direct application can be problematic due to its volatility, insolubility and potential skin irritation. The study tested the effects of eugenol and its nanoencapsulated form on human neutrophils and keratinocytes. While eugenol proved safe and beneficial to neutrophils, it showed cytotoxic effects on keratinocytes. However, when eugenol was encapsulated in nanocarriers, it significantly reduced these cytotoxic effects. In vivo tests using a mouse model of irritant contact dermatitis showed that nano-encapsulated eugenol (NCEUG) effectively reduced inflammation, ear swelling and leukocyte infiltration and IL-6 levels compared to standard eugenol solution. This suggests that nano-encapsulation of eugenol not only mitigates its irritant effects, but also enhances its therapeutic properties, making it a promising treatment for contact dermatitis [50].

Summary

Carvacrol and eugenol have shown potential antibacterial and antifungal activity against various fungal and bacterial species. They may provide effective alternative therapies for various bacterial and fungal infections. Carvacrol, found in plants such as oregano and thyme, and eugenol, mostly found in clove oil, are effective against pathogens such as Candida species and Escherichia coli. Research has underscored their potential for treating conditions such as oral and vaginal candidiasis, where they have proven as effective as standard treatments in reducing symptoms and eliminating the infection. For example, carvacrol and eugenol significantly reduced Candida colony-forming units in the mouth and eliminated fungi in the vagina, respectively. Their mechanisms of action include disrupting cell membranes, inhibiting key biosynthetic processes in pathogens, and enhancing the efficacy of conventional antimicrobials through synergistic effects. Moreover, their antifungal properties include treatment of diseases caused by dermatophytes and fungi responsible for keratitis, as indicated by their ability to inhibit growth, reduce virulence and disrupt biofilms. This dual functionality makes carvacrol and eugenol particularly valuable in medical conditions where there is resistance to standard drugs. In summary, the integration of carvacrol and eugenol into treatment regimens can significantly improve therapeutic outcomes against fungal and microbial infections. Their natural origins combined with their powerful bioactive properties support their potential as alternatives to synthetic antimicrobials.

Disclaimer

This article was written for educational purposes and is intended to raise awareness of the substance being discussed. It is important to note that the substance discussed is a substance, not a specific product. The information contained in the text is based on available scientific research and is not intended to serve as medical advice or promote self-medication. The reader should consult any health and treatment decisions with a qualified health professional.

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