Modeling The Sensitivity Profile Of Different Genotypes Of Methacycline-Resistant Staphylococcus Aureus To The Essential Oils Of Cymbopogon Citratus And Lippia Origanoides

Background: Bacterial resistance to conventional antibiotics poses a growing threat to human and animal health, prompting increased research into alternative treatments. Essential oils have emerged as promising candidates due to their ability to disrupt bacterial structures and processes. Methicillin-resistant Staphylococcus aureus (MRSA) remains a major concern in both human and animal communities, particularly in cases of bovine mastitis, where its resistance to multiple drugs complicates treatment. Although essential oils like those from Cymbopogon citratus and Lippia origanoides have shown potential antimicrobial properties, there is still a need for more consistent methods to evaluate their effectiveness, especially across different MRSA genotypes. This study investigates the antimicrobial activity of these essential oils against various MRSA strains isolated from bovine mastitis and analyzes the sensitivity patterns using advanced techniques like multivariate curve clustering, addressing critical gaps in our current understanding of essential oil efficacy. Materials and Methods: Nine MRSA strains were collected from cows with subclinical mastitis in northern Minas Gerais, Brazil. The strains were identified using PCR with the femA gene and classified into 10 genotypic profiles through RAPD-PCR. After being stored and reactivated, the strains were tested for antimicrobial susceptibility. Essential oils from C. citratus (OECC) and L. origanoides (OELO) were extracted by steam distillation, and their chemical composition was analyzed by gas chromatography-mass spectrometry. The antimicrobial activity of the oils was evaluated using the disk diffusion method, with varying concentrations applied to MRSA cultures. The diameter of inhibition zones was measured, and statistical analysis, including Tukey's test, quadratic regressions, and multivariate clustering, was used to compare the oils’ effects across different MRSA genotypes and other variables. Results: The main components of OECC were geranial (31.89%), β-myrcene (25.37%), and neral (24.62%), while OELO contained carvacrol (29.75%), o-cymene (15.33%), and γ-terpinene (11.03%). Both oils demonstrated dose-dependent antimicrobial activity against MRSA, with OECC effective at a concentration of 30 µl/ml and OELO at 60 µl/ml. Multivariate analysis revealed similar inhibition patterns across different MRSA genotypes, providing insight into how these oils’ effects can be interpreted in quantitative terms. Notably, OELO's antimicrobial activity against MRSA has not been reported before, and the study highlights the novel use of both oils on MRSA strains isolated from bovine milk. Conclusion: The study showed that C. citratus and L origanoides essential oils had varying effects on different MRSA genotypes, with the inhibition influenced by factors like genotypic profile and location. These results open the door for further research to explore how these oils affect genetically distinct strains and to uncover the mechanisms behind their antimicrobial action