Enhanced antimicrobial efficacy of a vancomycin/zinc oxide/chitosan nanocomposite via Bacillus licheniformis-mediated biomodification

Recognition of antimicrobial resistance (AMR) is crucial for a strong publication. Drug-resistant microbes, such as Candida albicans, methicillin-resistant Staphylococcus aureus (MRSA), Escherichia coli, Proteus mirabilis, and Klebsiella pneumoniae, pose a significant health threat. There is an urgent need for innovative and synergistic therapies. The new engineered nanocomposite system, zinc oxide/chitosan nanocomposite loaded with vancomycin (VA/ZnO/CS), directly addresses this challenge by aiming to enhance or restore the efficacy of existing drugs. Zinc oxide nanoparticles (ZnO NPs) were biosynthesized using Bacillus licheniformis ATCC 4527, and then combined with chitosan (CS) and vancomycin (VA) through a green chemical method. The nanocomposite that was produced was characterized using various techniques. The results of UV-Vis spectroscopy showed an adsorption peak at 348 nm. The material matrix of the nanocomposite contains ZnO NPs and numerous active groups, as indicated by the results of X-ray diffractometer (XRD) and Fourier transform infrared spectroscopy (FTIR). Images captured by transmission electron microscopy (TEM) showed that the VA/ZnO/CS particles were spherical with an average size of 78 ± 2.3 nm. The mean crystallite size of the nanocomposite was calculated using the Scherrer equation from the XRD data (79.38 nm) which closely matched the dimensions of the ZnO core observed in the TEM images (78 ± 2.3 nm). The antimicrobial activity of VA/ZnO/CS was tested against Bacillus cereus ATCC 14,579, MRSA ATCC 33,592, P. mirabilis AUF1, Klebsiella pneumoniae ATCC 11,296, and Candida albicans ATCC 10,231. Compared to common drugs like fluconazole and vancomycin, VA/ZnO/CS demonstrated significantly higher levels of biocidal activity in the agar well-diffusion test, minimum inhibitory concentration (MIC), and minimum microbicidal concentration (MMC). The antimicrobial activity was found to be dependent on the dose of nanocomposite with higher doses resulting in increased antimicrobial inhibition. The prepared nanocomposite achieved a complete biocidal effect against the investigated microorganisms with 5-15 µg/ml, while conventional drugs required 25-30 µg/ml. The powerful antimicrobial action of VA/ZnO/CS was demonstrated by the TEM micrographs of C. albicans showing malformations and distortions of cell structure, including cell wall destruction and the emergence of vacuoles. Based on the results, the green synergy between ZnO/CS nanocomposite and VA will provide an effective biomaterial for treating infections and microbial diseases.