Antibacterial Evaluation of Tricyclic Antidepressants Against S. aureus and the Possible Pathways of the Mechanism of Action

The resistance of <i>Staphylococcus aureus</i> to conventional pharmacological treatments has gradually increased. Thus, new therapeutic strategies are needed. Three tricyclic antidepressants (TCAs), amitriptyline (AMT), nortriptyline (NOR), and clomipramine (CLO), stand out with potential in this regard. Thus, the objective of this study was to evaluate the antibacterial activity of TCAs against <i>S. aureus</i>. The methodology used broth microdilution, checkerboard, flow cytometry, fluorescence microscopy, and scanning electron microscopy (SEM) techniques. The results showed that the minimum inhibitory concentration (MIC) of AMT was 256 µg/mL, while the MIC of NOR was 128 µg/mL, and the MIC of CLO was between 64 and 128 µg/mL. The TCAs exhibited bactericidal activity. In the analysis of the association with oxacillin (OXA), AMT exhibited 75% synergism, while NOR and CLO obtained 62.5%. In combination with vancomycin (VAN), AMT and NOR presented 100% additive interactions, while CLO exhibited 62.5% indifferent interactions. The mechanism of TCAs, isolated and combined with OXA, was associated with a reduction in cell viability, resulting from their action on the bacterial genetic material and generation of oxidative stress. Furthermore, the action of the drugs produced intense morphological changes in the bacterial cells. In conclusion, TCAs are a potential alternative for antistaphylococcal therapy.