Title : Combination of essential oils and tetracycline to restore antibiotic activity against tetracycline-resistant Salmonella enterica strains
Abstract:
Abstract: Short Description of what will be discussed during the presentation (about 250 - 500 words) Salmonellosis is the second foodborne zoonosis in Europe. Pig meat and derived products are important sources for salmonellosis in humans, because of a high prevalence of Salmonella spp. on pig carcasses (EFSA, 2021). Administration of oral antibiotics is very common in intensive pig farms and contributes to the development of antimicrobial resistance (AMR). Salmonella spp. strains isolated from the swine food chain are generally resistant to more than three classes of antibiotics (Lauteri et al., 2022), among which the tetracyclines compounds have gained common attention (EFSA, 2022). Hence, the “One Health” approach to contain AMR is mandatory. Nowadays, alternative strategies have been evaluated to overcome AMR, including the use of essential oils (EOs) as antimicrobials. EOs strike multiple targets in bacterial cells and therefore make it difficult to stimulate the development of resistance phenomena (De?irmenci & Erkurt, 2020).
Considering this, the present study evaluates the antimicrobial effectiveness of the combination of tetracyclines compounds (Tc) with three EOs: Coridothymus capitatus (CC), Thymus capitatus L. (TC), and Thymus serpyllum (TS) EOs against 11 tetracycline-resistant Salmonella enterica strains isolated from the swine food chain. The synergistic effect between tetracycline and each EOs was evaluated calculating the Fractional Inhibitory Concentration index. Through the Principal component analysis (PCA) analysis, the influence of the EOs phytocomplex was assessed, to understand which compounds determined the antimicrobial activity in the presence of Tc. The combination between the EOs and Tc compounds caused a clear reduction of the effective antibiotic concentration (from 256 to 4 μg/mL) for each S. enterica strain, suggesting a restoration of susceptibility to the treatment. Moreover, the combination between Tc and CC EO exhibited the highest synergistic effect (73%). The positive correlation observed between the EOs terpenoid compounds and Tc, through PCA analysis, suggested that carvacrol, linalool, sabinene and thymol could exert a synergistic effect with Tc compounds. Hence, this study demonstrates that the use of EOs could represent a promising strategy to restore the bacterial stress caused by Tc treatment, overcoming resistance in S. enterica.
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- EFSA, Zoonoses, foodborne outbreaks and antimicrobial resistance guidance for reporting 2022 data. EFSA J. 2023, 20:EN-7827.
- Lauteri, C., Maggio, F., Serio, A., Festino, A.R., Paparella, A., Vergara, A. Overcoming multidrug resistance in Salmonella spp. isolates obtained from the swine food chain by using essential oils. An in vitro study. Front. Microbiol., 2022, 12:808286.
Audience take Away:
- The combination of essential oils with antibiotics could be a strategy to overcome AMR, restoring bacterial susceptibility to the treatments.
- Corydothymus capitatus EO showed the highest synergistic effect with tetracyclines.
- PCA showed that some EO components, and namely carvacrol, linalool, sabinene and thymol, can exert interesting synergistic effects with tetracycline compounds.
