Antibacterial and antibiotic resistance modulation potentials of Nephelium lappaceum (Sapindaceae) against multidrug-resistant Pseudomonas aeruginosa

Pseudomonas aeruginosa is a bacterium responsible for nosocomial infections, and infections caused by multidrug-resistant (MDR) P. aeruginosa have a high mortality rate. Faced with this health challenge, this study aimed to assess the antibacterial activity, modes of action, and antibiotic resistance modulation effect of the epicarp (NLE) and seed (NLS) methanol extracts of Nephelium lappaceum on a panel of MDR P. aeruginosa . The antibacterial activity of N. lappaceum extracts and their effect in combination with antibiotics were assessed using the microdilution method and checkerboard assay, respectively. The modes of action of the active extract (NLE) were assessed on H + /ATPase proton pump activity, membrane permeability, bacterial kinetics, and catalase activity, using known methods. The phytochemical composition of the extracts was determined using standard methods. The tested extracts exhibited antibacterial activity, with MICs ranging from 64 to 2048 µg/ml. NLE exhibited the highest activity (MIC ≤ 64 µg/ml), particularly on P. aeruginosa K109 and K170. It increased the membrane permeability of P. aeruginosa K109 and showed no significant inhibitory effect on catalase and H + /ATPase proton pump of this isolate. At its sub-inhibitory concentrations (MIC/4 and MIC/8), NLE enhanced the activity of ciprofloxacin, levofloxacin, and doxycycline by 2 to 128-fold. Moreover, it displayed a synergistic effect (ƩFIC ≤ 0.5) with these antibiotics, especially with ciprofloxacin and levofloxacin. Phytochemical screening revealed that NLE contained all the tested phytochemical classes and had the highest phenolic, flavonoid, and tannin contents compared to NLS. This study provides a baseline for considering N. lappaceum epicarp extract as a potential candidate for the treatment of P. aeruginosa -related illnesses involving MDR phenotype. • Nephelium lappaceum epicarp (NLE) and seeds (NLS) methanol extract tested • NLE was active on all the tested MDR P. aeruginosa , with MIC ≤ 64 µg/mL as the highest activity • NLE enhanced ciprofloxacin, levofloxacin, and doxycycline activity by 2 to 128-fold • NLE increased the membrane permeability of P. aeruginosa K109. • NLE had the highest phenolic, flavonoid, and tannin contents