*2.6. Antibacterial Activity*

The antibacterial effectiveness of *Origanum compactum* hydroethanolic extract was tested against two Gram-negative bacteria (*Escherichia coli* and *Salmonella typhimirium*) and two Gram-positive bacteria (*Staphyloccocus aureus* and *Listeria monocytogenes*) through a broth microdilution assay. Tested concentrations for MIC and MBC were 166.66, 83.33, 41.66, 20.83, 10.41, 5.20, 2.60, 1.30, 0.65 and 0.32 mg/mL. Table 3 summarizes the results. The MIC values for *Origanum compactum* hydro-ethanolic extract against all tested bacteria ranged from 1.30 ± 0.11 to 41.66 ± 0.19 mg/mL. The extract displayed a bacteriostatic activity against *Escherichia coli* and *Salmonella typhimirium* with MBC/MIC values of 32 and 8, respectively, and a bactericidal activity against and *Staphyloccocus aureus* and *Listeria monocytogenes* with MBC/MIC values of 4 and 2, respectively.

**Table 3.** Determination of minimum inhibitory concentration and minimum bactericidal concentration exhibited by *Origanum compactum* ethanolic extract against bacterial strains (mg/mL).


The ethanolic extract of *Origanum compactum* was previously tested against *Escherichia coli* and *Staphyloccocus aureus*, and both strains were sensible to the extract [3].

The resistance of *Escherichia coli* and *Salmonella typhimirium* is related to the fact that Gram-negative bacteria are more resistant than Gram-positive bacteria to the majority of antibacterial agents. The resistance of Gram-negative bacteria is attributed to the hydrophilic nature of the membrane, which prevents the passage of hydrophobic molecules such as polyphenols. *Escherichia coli* have a bacterial wall where lipopolysaccharides are abundant and inhibit hydrophobic molecules from passing through the membrane [3].

The antibacterial effect of the ethanolic extract of *Origanum compactum* could be attributed to its phenolic composition. Indeed, the antibacterial activity of rosmarinic acid has been studied and proved against several bacterial strains. Even so, the molecular mechanisms and pathways explaining its biological activities have not been thoroughly investigated [30].
