Antibiofilm potential of biogenic magnesium oxide nanoparticles against multidrug resistant gram-negative bacteria

Antibiotic resistance among Gram-negative bacteria, particularly those capable of forming biofilms, has become a serious clinical challenge with limited treatment options. In this study, magnesium oxide nanoparticles (MgO NPs) were synthesized using a green, cost-effective approach based on aqueous leaf extract of Cymbopogon citratus (lemongrass) and evaluated for their antibacterial and antibiofilm potential against multidrug resistant (MDR) clinical isolates of Acinetobacter baumannii, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Escherichia coli. Minimum inhibitory concentration (MIC) values determined by broth microdilution ranged from 250 to 500 µg/ml, and minimum bactericidal concentration (MBC) values ranged from 1000 to 2000 µg/ml. Antibacterial activity assessed by the well diffusion method was dose-dependent, with inhibition zones ranging from 18 to 28 mm. The effect of MgO NPs on biofilm formation and eradication of pre-formed biofilms was evaluated using microtiter plate assay with crystal violet staining. Percentage inhibition of biofilm formation ranged from 27 to 97.1%, while eradication of established biofilms ranged from 51.9 to 96.4%. Exposure to sub-inhibitory concentrations of MgO NPs led to a 2 to 3-fold increase in reactive oxygen species (ROS) production in treated cells compared to controls. MgO NPs also significantly reduced the protein, carbohydrate, and DNA content of the biofilm matrix. Swimming, swarming, and twitching motility were markedly reduced in treated isolates. Congo red agar assay confirmed that slime production was inhibited following NP treatment. These findings suggest that biogenically synthesized MgO NPs hold considerable promise as antibacterial and antibiofilm agents against MDR Gram-negative pathogens.