Selenocompounds as Potent Efflux Pump Inhibitors on Gram-positive Bacteria

In recent years, selenocompounds have gained increasing attention as potential anticancer and antibacterial agents. Several selenoderivatives have been confirmed to act as MDR efflux pump inhibitors, based on their in vitro results against the bacterial AcrAB-TolC system and the cancer MDR efflux pump P-glycoprotein. Efflux pumps can contribute directly or indirectly to the virulence of bacteria, as they can reduce the intracellular concentration of antibacterial substances by expelling them out of the cell. The present work aims to study the antibacterial and efflux pump inhibiting properties of four families of selenoesters, namely aspirin-selenoesters, phenone-selenoesters, hydroxy-selenoesters, and benzyl-selenoesters. The real-time ethidium bromide accumulation assay confirmed that these derivatives inhibited the efflux systems of methicillin-resistant Staphylococcus aureus (MRSA) without exerting any antibacterial effect. The relative expression of efflux pump gene of NorA transporter was also monitored in the presence of the most potent derivatives on reference S. aureus, finding that these derivatives could change the expression of the tested efflux pump gene. Regarding the anti-biofilm activity, aspirin-selenoesters, benzyl-selenoesters, and hydroxy-selenoesters could efficiently inhibit the biofilm production of the MRSA strain. It can be concluded that selenocompounds could act as efflux pump inhibitors, thus reducing the virulence of biofilm-producing bacteria.