Evaluation of Elaiophylin extracted from Streptomyces hygroscopicus as a potential inhibitor of the NorA efflux protein in Staphylococcus aureus: An in vitro and in silico approach

Compounds capable of inhibiting the efflux pump mechanism are a promising alternative against bacterial resistance because, when combined with antibiotics, they can increase the effectiveness of these drugs by inhibiting active efflux. Elaiophylin, derived from Streptomyces hygroscopicus, is a natural antibiotic that exhibits a variety of biological activities, including antibacterial activity. However, its potential as an inhibitor of the bacterial efflux mechanism has not been investigated. This study evaluated the ability of Elaiophylin to inhibit the NorA efflux pump in Staphylococcus aureus strains. Therefore, tests were performed to obtain the Minimum Inhibitory Concentration (MIC) and to verify the ability of Elaiophylin to potentiate the MIC of the antibiotic Norfloxacin and Ethidium Bromide (EtBr), known substrates of NorA efflux. Real-time PCR and molecular docking assays were also performed to assess the potential of Elaiophylin against NorA. The strains SA-1199 (wild type) and SA-1199B (NorA over-expressed) of S. aureus were used for this study. The results showed that Elaiophylin significantly decreased the MIC of Norfloxacin and EtBr, increasing the activity of these substrates against S. aureus, which carries the efflux protein NorA. However, Elaiophylin provided a non-significant reduction in norA gene expression, however, molecular docking demonstrated a high binding affinity between Elaiophylin and NorA efflux protein, indicating that Elaiophylin can act as a potential NorA in S. aureus.