## 4 Discussion  
The present study demonstrates significant differences in antimicrobial activity when essential oils are combined with vitamin C, compared to their individual application. Notably, the combination of oregano essential oil (OEO) and vitamin C resulted in a pronounced decrease in MIC, MBC and MFC values against _E. coli_ and _C. albicans_, suggesting a synergistic effect. The MIC of OEO combined with vitamin C was several-fold lower than that of pure OEO, indicating that vitamin C enhances antimicrobial efficacy. However, a potential antagonistic effect was observed against _S. aureus_, where the combination was less effective than the essential oil alone. A similar pattern was observed for thym essential oil (TEO) combined with vitamin C. While no synergy was detected against _E. coli_ and _S. aureus_, enhanced antifungal activity was noted against _C. albicans_. Importantly, vitamin C alone did not exhibit antimicrobial activity at the tested concentrations (1-20 mg/mL), which aligns with previous studies reporting its lack of direct antimicrobial effects in neutral  
Figure 6: Functional clustering of predicted molecular targets modulated by carvacrol, thymol and vitamin C. Each node represents a biological process, with key proteins or genes indicated in parentheses. Lines denote functional associations. The clusters highlight processes relevant to antimicrobial action and host modulation, including oxidative stress, signal transduction, mitochondrial biogenesis, DNA replication, quorum sensing and cell wall integrity. conditions [32; 33]. This observation supports the idea that vitamin C may modulate the physicochemical environment rather than act as a direct antimicrobial agent [34; 35; 36]. Moreover, vitamin C, being a weak organic acid, may reduce the pH of the surrounding medium, thereby influencing the ionization and diffusion of essential oil constituents [34; 37; 38]. The observed antagonistic effect against _S. aureus_ may reflect interference between the molecular targets or competitive interactions among active compounds, which has been documented in previous studies on essential oil combinations [39]. These findings support the hypothesis that vitamin C may act as a synergistic adjuvant, enhancing the antimicrobial effects of certain plant-derived compounds. This is consistent with evidence that vitamin C and related redox-active compounds can influence immune signaling pathways such as NF-\(\kappa\)B and Nrf, which are also known to modulate inflammatory responses and cellular defense mechanisms [40; 41; 42]. However, the effects are strain-specific, highlighting the complexity of phytochemical interactions. Similar synergistic, additive and antagonistic interactions have been reported in the literature [43; 44]. For instance, [PERSON] et al. reported antagonistic effects when thyme oil was combined with parsley, lavage and basil oils [44]. Likewise, the combination of amoxicillin with methanolic extracts of _Tetraclinis articulata_ showed reduced activity against _S. aureus_[45]. In fact, true synergy is relatively rare, whereas additive or even antagonistic effects are more commonly observed among plant-derived compounds [46; 47]. One possible explanation for the antagonism observed against _S. aureus_ is the competition between bioactive components of essential oils for shared molecular targets, or chemical interactions that reduce efficacy [35; 43]. Additionally, vitamin C might alter the ionization state of essential oil constituents through pH modulation, which can influence their biological activity. This mechanism has been discussed in relation to acidic shifts in the medium that affect essential oil solubility and reactivity [37; 38]. The absence of a pH-matched control in this study limits our ability to fully separate pH effects from compound-specific interactions [39]. This limitation has now been acknowledged. Discrepancies between broth and agar dilution methods were also observed, particularly for _S. aureus_.