**3. Antimicrobial activity of OEO**

The OEO's antimicrobial activity has been attributed to its compounds such as carvacrol and thymol, which are the main constituents responsible for the strong antimicrobial effects of oregano essential oil [2, 6]. They exhibit broad-spectrum activity against various bacteria, fungi, and even some viruses. These compounds disrupt the cell membranes and inhibit the growth and proliferation of microorganisms [10, 17]. The OEO damage disrupts in-membrane integrity, which affects pH homeostasis and equilibrium of inorganic ions [18]. Carvacrol has been shown to alter the electrolyte balance because of decrease in the intracellular potassium, increase in the extracellular potassium, and consequently the bacterial membrane potential [19]. But the effect of OEO goes beyond the bacterial membrane because a transfer of monoterpene to inside of bacteria and the interaction with their components is also suggested [20]. Another mechanism of antibacterial action has been found for the OEO, the inhibition of quorum sensing (QS) in *Escherichia coli* and *Pseudomonas aeruginosa*. The QS is a mechanism that modulates the expression of genes that allow to recognize the bacterial population density through the accumulation of specific signaling molecules to ensure the survival and pathogenesis [21]. The OEO has proven to have a wide spectrum of antibacterial activity and is one of the most inhibitory species. However, there are few references that compare the antimicrobial activity of *Origanum* gender species versus *Lippia origanoides* as well as the antibacterial activity against pathogenic and beneficial bacterial strains to animal health and production.

Our studies compared the minimum bactericidal concentration (MBC) of carvacrol, *O. vulgare* spp., and *L. origanoides*. Carvacrol presented the lowest value of MBC against *E. coli* (0.006 mg/mL) and *Salmonella typhimurium* (0.098 mg/mL), followed by *L. origanoides* against *E. coli*, and *O. vulgare L*. ssp. Hirtum and *O. vulgare* L. against *S. typhimurium*. The highest bactericidal activity against *S. enteritidis* was presented with carvacrol, *O. vulgare* L. ssp. Hirtum (high carvacrol), and *L. origanoides* (high thymol). In contrast, the lowest bactericidal activity was presented against beneficial bacteria with a higher value of MBC when they were compared with pathogenic bacteria. Except to *Bifidobacterium breve*, while carvacrol presented the highest bactericidal activity (1.56 mg/mL), L. *origanoides* had the lowest activity (50 mg/mL). The *O. majorana* essential oil showed the lowest bactericidal activity against pathogenic and beneficial bacteria. The higher bactericidal activity against pathogenic bacteria

was associated with the content of phenolic components carvacrol or thymol with respect to species such as *O. majorana* with a high content of sabinyl compounds. This study found that the OEO had a selective bactericidal effect against pathogenic and beneficial bacteria. The beneficial bacteria *Lactobacillus* and *Bifidobacterium* were less sensitive to OEO than the pathogens *Salmonella* and *E. coli* to both carvacrol and OEO high carvacrol and high thymol. These results give to OEO a potential use to maintain the intestinal eubiosis [12]. Other studies also concluded that the essential oil of *Lippia origanoides* H.B.K. presented antimicrobial action against *Staphylococcus aureus*, *Escherichia coli*, and *Candida albicans* strains [22]. The OEO from *Lippia origanoides* high thymol grown in Brazil also demonstrated antimicrobial activities against the foodborne bacteria *Bacillus cereus*, *B. subtilis*, and *Salmonella typhimurium*, but not against *Pseudomonas aeruginosa* [23]. It can be concluded that *L. Origanoides* presents a potential for the development of new phytotherapeutics.
