Synergistic Antibacterial Effect of Casein-AgNPs Combined with Tigecycline against Acinetobacter baumannii

Acinetobacter baumannii (A. baumannii) is a common and challenging pathogen of nosocomial infections, due to its ability to survive on inanimate objects, desiccation tolerance, and resistance to disinfectants. In this study, we investigated an antibacterial strategy to combat A. baumannii via the combination of antibiotics and silver protein. This strategy used a functional platform consisting of silver nanoparticles (AgNPs) resurrected from silver-based calcium thiophosphate (SSCP) through casein and arginine. Then, the silver protein was combined with tigecycline, the first drug in glycylcycline antibiotic, to synergistically inhibit the viability of A. baumannii. The synergistic antibacterial activity was confirmed by the 96-well checkerboard method to determine their minimum inhibitory concentrations (MIC) and calculated for the combination index (CI). The MIC of the combination of silver protein and tigecycline (0.31 mg/mL, 0.16 µg/mL) was significantly lower than that of the individual MIC, and the CI was 0.59, which indicates a synergistic effect. Consequently, we integrated the detailed synergistic antibacterial properties when silver protein was combined with tigecycline. The result could make for a promising approach for the treatment of A. baumannii.