Polymyxin combined with essential oil: one alternative strategy for combating polymyxin-resistant .

Multidrug-resistant infections present a critical public health due to scarce treatment options and high mortality. L. essential oil (O.geo) is a natural resource rich in eugenol known for its antimicrobial activity. O.geo may exert effective antimicrobial activity against polymyxin-resistant Klebsiella pneumoniae and, when combined with Polymyxin B (PMB), may exhibit a synergistic effect, enhancing treatment efficacy and reducing antimicrobial resistance. This study aims to investigate the antimicrobial activity of O.geo against polymyxin-resistant using tests and an model. The O.geo was obtained by hydrodistillation followed by gas chromatography. The MIC and antibiofilm activity were determined using broth microdilution. Checkerboard and time-kill assays evaluated the combination of O.geo and polymyxin B (PMB), whereas a protein leakage assay verified its action. Eugenol (39.67%) was a major constituent identified. The MIC of the O.geo alone ranged from 128 to 512 µg ml. The fractional inhibitory concentration index (0.28) and time-kill assay showed a synergism. In addition, O.geo and PMB inhibited biofilm formation and increased protein leakage in the plasma membrane. The treatment was tested using a model, and significantly increased survival without toxicity was observed. O.geo could be used as a potential therapeutic alternative to combat infections caused by multidrug-resistant bacteria, especially in combination with PMB.