Inhibition of quorum sensing regulation and stress tolerance by Rhodomyrtus tomentosa extracts and rhodomyrtone as an alternative treatment for zoonotic pathogens

Background and Aim: Staphylococcus aureus is a zoonotic pathogen with significant public health and economic implications. Its ability to tolerate environmental stress and regulate virulence through quorum sensing contributes to its persistence and pathogenicity. Rhodomyrtus tomentosa and its bioactive compound rhodomyrtone have demonstrated antimicrobial properties against Gram-positive, multidrug-resistant bacteria. This study aimed to evaluate the effects of these agents on quorum sensing inhibition and stress tolerance in S. aureus and Pseudomonas aeruginosa, providing insights into their potential as alternative antimicrobial strategies. Materials and Methods: The anti-quorum sensing activity of R. tomentosa extracts was assessed using Chromobacterium violaceum as a bioindicator. In addition, the effects on P. aeruginosa swarming motility were evaluated. Stress tolerance in S. aureus was examined by subjecting treated cells to acidic (pH = 5.0), alkaline (pH = 9.0), osmotic (7.5% NaCl), heat (43°C), and oxidative (1 mM H₂O₂) stress conditions. The survival rates were determined through colony-forming unit (CFU) counts following treatment with rhodomyrtone and ethanol leaf extracts. Results: The ethyl acetate fraction of R. tomentosa leaf extract exhibited the highest violacein inhibition, followed by the ethanol extract. At 256 μg/mL, these extracts permitted P. aeruginosa colony formation but inhibited its swarming motility. Regarding stress tolerance, no surviving S. aureus cells were detected under any stress condition after 3–6 h of treatment with 2 × minimum inhibitory concentration (MIC) (1 μg/mL) of rhodomyrtone. In addition, 4 × MIC (128 μg/mL) of the ethanol leaf extract inhibited pathogen survival under all tested stress conditions except for alkaline and oxidative stresses. Conclusion: The findings suggest that R. tomentosa extracts and rhodomyrtone effectively inhibit quorum sensing and stress tolerance, offering a promising alternative antimicrobial approach. These compounds could be utilized in veterinary medicine and food safety to mitigate zoonotic pathogen contamination and combat antibiotic-resistant infections. Keywords: anti-quorum sensing, Pseudomonas aeruginosa, rhodomyrtone, Rhodomyrtus tomentosa, Staphylococcus aureus, stress tolerance.