Enhanced antibacterial efficacy of Lysinibacillus fusiformis-mediated bimetallic silver-gold nanocomposites against multidrug-resistant chronic wound bacterial pathogens

Numerous people have lost their lives due to diseases associated with antimicrobial resistance (AMR). Studies have reported that Multidrug-resistant (MDR) bacterial infections significantly contribute to mortality linked to AMR. It is vital to develop novel antibacterial compounds against these MDR bacteria. Hence, we produced silver-gold nanocomposites (Ag-Au NCPs) colloidal suspension (CS) with cell biomass of Lysinibacillus fusiformis in three ratios; 1:1 (A), 3:7 (B) and 7:3 (C). The changes in color of the CS were observed visually and confirmed with UV–vis spectroscopy. The synthesized Ag-Au NCPs were screened for antibacterial efficacies using well-diffusion method. The MIC and MBC of Ag-Au NCPs showing potential antibacterial activities were examined with microtitre plate. The CS of Ag-Au NCPs with antibacterial efficacies was oven-dried. The structural and spectral features of dried Ag-Au NCPs were analyzed with SEM, DLS, TEM, EDAX, FTIR and XRD. After 4–8 hours, the CS of three Lysinibacillus fusiformis- mediated Ag-Au NCPs each displayed a single peak (636 nm (A), 634.5 nm (B) and 600.5 nm (C)). The promising Ag-Au NCPs are sphere-shaped and clustered in pairs. The DLS measurements indicated a mean size distribution and polydispersity index of 113.27 ± 0.67 nm and 0.1813 ± 0.0137, respectively; however, TEM confirmed an average diameter of 19.13 ± 1.86 nm. The EDAX confirmed presence of 66.2 % zerovalent silver (3.0 keV) and 13.4 % zerovalent gold (2.0 keV). The FTIR established presence of methyl bonds, amine symmetric stretch and linkages. In addition, XRD confirmed Bragg’s peaks corresponding with standard planes of crystalline silver and gold. The Ag-Au NCPs demonstrated enhanced antibacterial efficacy against 77.78 % of tested MDR bacteria, particularly against Pseudomonas aeruginosa (MIC 78.125 µg/mL; MBC 156.25 µg/mL) and Enterobacter hormaechei (MIC 78.125 µg/mL; MBC 312.5 µg/mL). These remarkable results demonstrate the strong potential of Ag-Au NCPs for treating MDR bacteria-infected chronic wounds. • The cell biomass of Lysinibacillus fusiformis intracellularly synthesized Ag-AuNCPs. • The Ag-AuNCPs are sphere-shaped with mean size distribution of 113.27 ± 0.67 nm and polydispersity index of 0.1813 ± 0.0137. • The TEM validated an average diameter of 19.13 ± 1.86 nm. • The EDAX confirmed 66.2 % zerovalent silver at 3.0 keV and 13.4 % zerovalent gold at 2.0 keV. • The Ag-AuNCPs showed enhanced antibacterial efficacy against the MDR bacteria (MIC 78.125 µg/mL; MBC 156.25–312.5 µg/mL).