Synergistic antimicrobial potential of Cinnamomum triplinerve essential oils combined with polymyxin B against multidrug-resistant Klebsiella pneumoniae.

Antimicrobial resistance, particularly in carbapenem-polymyxin-resistant Klebsiella pneumoniae (CPR-Kp), is a major global concern. This study evaluated the chemical composition and antimicrobial potential of Cinnamomum triplinerve essential oils against CPR-Kp. Essential oils from leaves (CTL) and bark (CTB) were extracted via hydrodistillation and analyzed by gas chromatography-mass spectrometry. Their antimicrobial activity, alone and combined with polymyxin B (PMB), was assessed through checkerboard assays, biofilm inhibition, cell membrane permeability, and scanning electron microscopy (SEM). Reactive oxygen species (ROS) production was also examined. Safety was evaluated via hemolysis and toxicity tests in Caenorhabditis elegans, which was also used as an infection model to attest combinations in vivo efficacy. (E)-Nerolidol was identified as the major component. CTL and CTB reduced the PMB minimum inhibitory concentration by 32-fold, demonstrating synergy and biofilm inhibition in combination. SEM confirmed bacterial death, though intracellular bacterial protein leakage was absent. CTL-PMB induced oxidative stress, unlike CTB-PMB. No hemolysis or toxicity was observed. Infected C. elegans treated with CTL-PMB and CTB-PMB showed survival rates of 77.77% and 27.29%, respectively. These findings highlight the in vitro and in vivo potential of C. triplinerve essential oils as adjuvants to PMB, offering a promising therapeutic strategy against CPR-Kp infections.