Green synthesis of silver nanoparticles using Acroptilon repens aqueous extract and their antibacterial efficacy against multidrug-resistant Acinetobacter baumannii.

BACKGROUND

Acinetobacter baumannii is a critical pathogen associated with hospital-acquired infections, particularly in burn and intensive care unit (ICU) patients, and is notorious for its high level of antibiotic resistance. This study aims to evaluate the antibacterial potential of silver nanoparticles (AgNPs) synthesized using Acroptilon repens extract as a promising alternative treatment for combating multidrug-resistant A. baumannii.

METHODS AND RESULTS

Twelve clinical isolates of A. baumannii were identified through biochemical testing. Antibiotic susceptibility testing using the Kirby-Bauer disk diffusion method revealed universal resistance to ceftazidime, amikacin, imipenem, gentamicin, ciprofloxacin, and piperacillin-tazobactam, while all isolates remained sensitive to colistin (p ≤ 0.05). AgNPs were synthesized using A. repens extract and characterized through transmission electron microscopy (TEM), scanning electron microscopy (SEM), particle size analysis (PSA), UV-Vis spectroscopy, X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (FT-IR). TEM analysis showed that the AgNPs had a spherical morphology with an average particle size of approximately 30 nm, while SEM confirmed their spherical shape and size distribution, ranging from 10 to 130 nm, with a mean size of 38.89 nm. UV-Vis spectroscopy confirmed the successful formation of AgNPs, indicated by a distinct broad absorption peak between 400 and 480 nm. XRD analysis validated the crystalline nature of the nanoparticles, with characteristic peaks at 2θ values of 38.21°, 46.28°, 64.57°, and 77.49°, corresponding to the (111), (200), (220), and (311) planes of face-centered cubic (fcc) silver. Antibacterial activity was evaluated by determining the minimum inhibitory concentration (MIC), which ranged from 50 to 400 µg/mL. The highest inhibitory activity was observed at 400 µg/mL. Gene expression analysis using quantitative real-time PCR (qRT-PCR) demonstrated downregulation of the oprD and carO porin genes following AgNP treatment. However, these reductions were not statistically significant (p = 0.302 and p = 0.198, respectively).

CONCLUSIONS

AgNPs synthesized from A. repens demonstrated strong antibacterial activity against multidrug-resistant A. baumannii. While downregulation of porin genes was observed, further investigation is required to elucidate the underlying mechanisms of action and assess their potential clinical applications. These findings support the potential of AgNPs as an alternative therapeutic strategy for addressing A. baumannii infections resistant to conventional antibiotics.