Assessment of Antibacterial Efficacy of Silver Oxide Nanoparticles and <i>Lactobacillus casei</i> Against the Clinical Isolates of <i>Acinetobacter baumannii</i>

Background and aims: Acinetobacter baumannii is recognized as a multidrug-resistant pathogen, notably associated with biofilm formation and antibiotic resistance in healthcare environments. The rising incidence of infections attributable to this organism highlights the urgent necessity for alternative therapeutic approaches. This study aimed to assess the antibacterial efficacy and antibiofilm activity of silver oxide nanoparticles and Lactobacillus casei against clinical isolates of A. baumannii. Methods: Overall, 150 A. baumannii isolates were collected from urine samples in Tehran, Iran, ensuring 80% statistical power and a 95% confidence level. The isolates were categorized by resistance profiles and treated with Ag NPs, L. casei supernatant, and their combination. Ag NPs were biosynthesized using L. casei extracts and characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy, and Fourier transform infrared spectroscopy. Antibacterial and antibiofilm effects were assessed using broth microdilution and microtiter assays. Finally, the analysis of variance and t-test were conducted in SPSS 26 (P&lt;0.05). Results: Based on the results, 18 isolates exhibited high resistance to β-lactam antibiotics and fluoroquinolones. Ag NPs (40 µg/mL) resulted in a 93.04% reduction in bacterial growth, while L. casei supernatant showed a 76.45% decrease. The combination of Ag NPs and L. casei supernatant demonstrated strong synergistic effects, achieving a 98.24% reduction in bacterial growth. Antibiofilm assays revealed a significant 95.3% inhibition of biofilm formation with the combination therapy (P&lt;0.001). Conclusion: This study highlights the potential of combining Ag NPs and probiotic-derived compounds as a novel approach to combat multidrug-resistant A. baumannii. These findings suggest promising avenues for enhancing antimicrobial therapies and addressing the challenge of antibiotic resistance in clinical settings.