Antimicrobial activity of diverse chemotypes ofLippia graveolensagainstAeromonas hydrophilaisolated from tilapia

Abstract Objetive This study aimed to evaluate the antimicrobial efficacy of essential oil (EO) from diverse chemotypes of Lippia graveolens against oxytetracycline-resistant Aeromonas hydrophila , which primarily affects the tilapia aquaculture ( Oreochromis sp) in Guatemala. Methodology L. graveolens were collected in three departments in Guatemala, the EO was obtained by hydrodistillation and characterized by gas chromatography and mass spectrometry (GC/MS). Subsequently, an antimicrobial assay was conducted by screening the disk and dilution susceptibility tests, and evaluation of synergistic interactions among the chemotypes, each test being carried out in triplicate. Results The analysis revealed the presence of twenty-seven compounds in the EO obtained from the chemotypes, the main class being monoterpene. The major constituents identified were cis-Dihydro-β-terpineol (8.84%) in chemotype I, carvacrol (51.82%) in chemotype II, and thymol (79.62%) in chemotype III. All EO chemotypes of L. graveolens demonstrated the ability to inhibit the A. hydrophila growth. Thymol chemotype exhibited the strongest inhibitory effect against bacterial growth, with a minimum inhibitory concentration (MIC) of 92.4 µg/mL and a minimum bactericidal concentration (MBC) of 184.8 µg/mL. Furthermore, the results suggest that there is no synergistic or additive effect when combining different chemotypes of L. graveolens . Conclusions This the first report of L. graveolens chemotypes exhibiting antimicrobial activity against oxytetracycline-resistant A. hydrophila . The findings suggest the chemotype thymol could be a potential treatment for infections in the tilapia aquaculture in Guatemala.