Antibacterial and Antibiofilm Activities of Colistin and Ceftazidime–Avibactam Conjugated Silver Nanoparticles

Multidrug-resistant (MDR) Gram-negative bacteria constitute a major global health concern, and the increasing resistance to last-line antimicrobial agents compels the urgent improvement of novel treatment strategies. The present study aims to produce colistin and ceftazidime-avibactam conjugated silver nanoparticles by eco-friendly synthesis method and to evaluate the antimicrobial and antibiofilm activities against MDR Gram-negative bacteria. The physicochemical characteristics of nanoparticles were analyzed through ultraviolet-visible spectrophotometry, high resolution-transmission electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy. Broth microdilution assay was conducted to detect minimum inhibitory concentration (MIC) levels of nanoparticles against MDR bacteria and reference strains. The antibiofilm efficacy was assessed by the crystal violet staining method, and the cytotoxic activity was determined using the MTT assay. The characterization analyses demonstrated spherical morphology (5.6-41.6 nm in diameter) and crystalline structures for the nanoparticles. The MIC levels of antibiotic-conjugated nanoparticles against reference strains and MDR clinical isolates ranged from 0.125 to 4 µg/mL, showing inhibitory concentrations (2-1024 fold) lower than that of free antibiotics (p < 0.05). Nanoparticles exhibited more effective biofilm activity on Pseudomonas aeruginosa PAO1 strain compared to free antibiotics, and showed no substantial inhibitory impact on cell viability, even at increased concentrations. The nanoparticles obtained by the green synthesis method could be promising agents in fighting against MDR Gram-negative bacteria.