Bacteriologically Derived Copper Nanoparticles as Novel Arsenal Against Multidrug-Resistant Pathogens

Antimicrobial resistance (AMR) has emerged as a global health menace which has caused millions of deaths and still continues to grow. The announcement of World Antimicrobial Awareness Week, 18–24 November 2022 by WHO further highlights the terrifying situation. Injudicious use of antibiotics is the major cause of emerging AMR. Therefore, new age antimicrobials are required for treating multi drug resistant (MDR) infections. In this quest, we synthesized novel green copper nanoparticles (BS-CuNPs) using cell free extracts of Bacillus subtilis (MTCC 441) and tested their bactericidal potential against various MDR pathogenic bacteria viz Staphylococcus aureus MRSA, E. coli Anp2A, E. coli Bi2A, Pseudomonas aeruginosa VTCCBAA2, Enterobacter cloacae Bu59. Antioxidant properties were also investigated using the DPPH and H₂O₂ radical scavenging techniques in terms of IC₅₀ (concentrations required for 50% inhibition) and IC₉₀ (concentrations required for 90% inhibition) values. The TEM micrographs of bacteriologically synthesized BS-CuNPs displayed size of 11.47 ± 2.6 nm with spherical configuration. BS-CuNPs also showed excellent colloidal and thermal stability in terms of zeta potential (− 26.9 meV) and thermogravimetric analysis (TGA). The MICs and MBCs of the BS-CuNPs against test MDR bacteria were ≤ 0.625 mg/ml which was significantly lesser (p < 0.05) than the same exhibited by CuNPs. The strongest effects were seen on Enterobacter cloacae Bu59 with MIC values of 0.156 mg/ml. The IC₅₀ and IC₉₀ of BS-CuNPs in DPPH assay exhibited significantly lower values, i.e. 42.97 and 128.31 µg/ml, respectively as compared to the chemically synthesized CuNPs, indicating potent antioxidant activity. These results from the performed studies clearly demonstrate the potential use of biogenic BS-CuNPs as novel antimicrobial in the field of biomedicine.