Search

Objective: Efflux pumps are transmembrane proteins associated with bacterial resistance mechanisms. Bacteria use these proteins to actively transport antibiotics to the extracellular medium, preventing the pharmacological action of these drugs. This study aimed to evaluate in vitro the antibacterial activity of 1,8-naphthyridines sulfonamides, as well as their ability to inhibit efflux systems of Staphylococcus aureus strains expressing different levels of the NorA efflux pump. Methods: The broth microdilution test was performed to assess antibacterial activity. Efflux pump inhibition was evaluated in silico by molecular docking and in vitro by fluorometric tests, and the minimum inhibitory concentration (MIC) was determined. The MIC was determined in the association between 1,8-naphthyridine and norfloxacin or ethidium bromide. Results: The 1,8-naphthyridines did not show direct antibacterial activity. However, they effectively reduced the MIC of multidrug-resistant bacteria by associating with norfloxacin and ethidium bromide, in addition to increasing the fluorescence emission. In silico analysis addressing the binding between NorA and 1,8-naphthyridines suggests that hydrogen bonds and hydrophilic interactions represent the interactions with the most favourable binding energy, corroborating the experimental data. Conclusion: Our data suggest that 1,8-naphthyridines sulfonamides inhibit bacterial resistance through molecular mechanisms associated with inhibition of the NorA efflux pump in S. aureus strains.

Introduction: The rapid emergence of multidrug-resistant bacteria has demanded the discovery of new drugs capable of inhibiting bacterial resistance mechanisms, such as those mediated by efflux proteins and β-lactamases. Objective: Considering the evidence indicating that phenylpropanoids are effective substances against bacterial resistance, the present study aimed to evaluate the antibacterial activity of compounds allylbenzene and allylanisol against the Staphylococcus aureus strain SA-K4414, which carries genes encoding the β-lactamase and QacA/B proteins. Methods: The Minimum Inhibitory Concentrations (MICs) were determined by the broth microdilution method. The expression of β-lactamase was verified through the association of the inhibitor sulbactam with the antibiotic ampicillin, while its inhibition was analyzed through the reduction of the penicillin MIC in the presence of phenolic compounds. The efflux pump inhibition was analyzed by the reduction in the MIC of the pump substrate ethidium bromide. The toxicity against Drosophila melanogaster was assessed by evaluating mortality and negative geotaxis through the fumigation method. Results: The results demonstrated that the phenylpropanoids failed to show relevant direct antibacterial activity, with MIC values above 1024 µg/mL. The association of allylbenzene and allylanisole with penicillin potentiated its antibacterial effect, reducing the antibiotic MIC (512 µg/mL) to 128 µg/mL and 256 µg/mL, respectively. The compounds also reduced the MIC of EtBr, indicating a possible inhibitory effect against the β-lactamase enzyme and the QacA/B efflux protein. Regarding toxicity, allylbenzene (after 12 h) and allylanisole (after 3 h) presented EC50 of 19.21 μL/mL and 11.07 μL/mL, respectively. These compounds also caused damage to the locomotor system of flies, which was potentiated following increasing concentrations and exposure period. Conclusion: It is concluded that the compounds allylbenzene and allylanisole can inhibit the resistance mechanisms mediated by the β-lactamase enzyme and the efflux protein QacA/B. However, due to the significant toxicity observed, further research is required to assess the safety of these compounds.