7--Carboxylic Acid-Substituted 3--Alkyl Difluoroquercetin; An Aztreonam-Potentiating Agent Against Carbapenemase-Producing Through Simultaneous Inhibition of Metallo-β-Lactamase and Efflux Pump.

Previously, we reported that 3--alkyl difluoroquercetins (di-F-Q) potentiates the antimicrobial activity of aztreonam (ATM) against metallo-β-lactamase (MBL)-producing through simultaneous inhibition of MBLs and efflux pumps. However, the ATM-potentiating activity of the 3--alkyl di-F-Q was observed only at high and potentially toxic concentrations (32 mg/L). As both MBLs and efflux pumps reside in the periplasm of Gram-negative bacteria, their inhibitors should accumulate in the periplasmic space. However, the outer membrane porins, the major entry pathway in Gram-negative bacteria, allow the passive diffusion of hydrophilic polar molecules across the outer membrane. Thus, we reasoned that the introduction of a polar substituent at 7-OH position of 3--alkyl di-F-Q would enhance its periplasmic concentration to result in potentiation of ATM at lower concentrations. The title compound exhibited inhibitory activity against NDM-1 as well as the efflux pump of , which resulted in synergistical potentiation of ATM. A combination of ATM (8 mg/L) and (8 mg/L) inhibited 80% of the ATM-resistant CPPA, while ATM alone did not show any inhibition. In addition, only 4 mg/L of was needed to reduce the MIC of ATM four-fold in ATM-resistant CPPA (n = 15). The time-kill data further supported the effectiveness of the combined treatment of ATM with , and the combination of ATM (1xMIC) with 8 mg/L of showed bactericidal effects in every bacterial strain tested (PA-002, , PA-003, , PA-014, , and PA-017, ) by reducing the bacterial loads by 5.1 log8.9 log. The title compound exhibited inhibitory activity against NDM-1 as well as the efflux pump of , and the combined inhibitory activity resulted in synergistical potentiation of ATM. It should be noted that most CPPA isolates tested were sensitized to 8 mg/L of ATM upon combination with 48 mg/L of .