EFFICACY OF GREEN SYNTHESISED SILVER-ZINC OXIDE NANOCOMPOSITES AGAINST MULTI-DRUG RESISTANT NON TYPHOIDAL SALMONELLA SPP.
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Date
2023-01-13
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COLLEGE OF VETERINARY AND ANIMAL SCIENCS, POOKODE, WAYANAD, KERALA VETERINARY AND ANIMAL SCIENCES UNIVERSITY
Abstract
The indiscriminate use of antibiotics has accelerated the emergence of multi- drug resistant (MDR) bacterial strains. In recent times, nanotechnology offers a novel alternative solution by providing a long-term strategy to combat the emergence of drug resistance. The present study evaluated the antibacterial efficacy of green synthesised silver-zinc oxide nanocomposites (Ag/ZnO NCs) against MDR strains of non- typhoidal Salmonella spp. (NTS). The green synthesis of Ag/ZnO NCs was attempted using the aqueous extract of leaves, stems, and rhizomes of Curcuma longa. Initially, the green synthesised Ag/ZnO NC was subjected to UV-Vis spectroscopy, Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and differential thermogravimetric analysis (DTA), powder X-ray diffraction (PXRD), field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). The green synthesised Ag/ZnO NCs exhibited absorbance peaks at 340 and 450 nm by UV-Vis spectroscopy, corresponding to Ag and ZnO nanoparticles (NPs), respectively, which was further confirmed by FTIR analysis. The TGA/DTA revealed an initial weight loss of around four per cent from 40oC to 100oC along with a progressive thermal degradation of Ag/ZnO NCs between 200 oC and 450 oC, which in turn corresponded to an exothermic peak at 320 oC. The PXRD analysis of Ag/ZnO NCs confirmed the face-centered cubic structure of AgNPs and hexagonal wurtzite structure with P63 mc symmetry of ZnO NPs. Further, FE-SEM analysis confirmed the agglomerated polycrystalline morphology of Ag/ZnO NCs with a characteristic spherical shape in TEM analysis. This study evaluated in vitro antibacterial efficacy of Ag/ZnO NCs against MDR-NTS strains (S. enterica Typhimurium and S. Enteritidis; n = 3 for each serotype). The minimum inhibitory concentration (MIC; 31.25μg/mL) and minimum bactericidal concentration (MBC62.50 μg/mL) were determined by employing the micro broth dilution technique. Later, Ag/ZnO NCs were assessed for their stability (high-end temperatures, physiological concentration of cationic salts, proteases, and pH); safety (chicken RBCs), and effecton gut beneficial microflora (Lactobacillus acidophilus, L. plantarum, and Paediococcus acidilactis). In general, the Ag/ZnO NCs tested stable at MIC concentration; however, a two-fold rise in the MBC value was detected. Besides, Ag/ZnO NCs tested safe with chicken RBCs; moreover, the beneficial gut microflora was not inhibited. Furthermore, the in vitro time-kill kinetic assay of MDR-NTS strains treated with Ag/ZnO NCs revealed a complete clearance at 240 min, alike meropenem control. In brief, the green synthesised Ag/ZnO NCs were found to exhibit antibacterial activity against the tested MDR-NTS and were tested safe and stable. Overall, the study demonstrated a facile, eco-friendly method for the synthesis of Ag/ZnO NCs, which could be employed as a potential therapeutic alternative candidate.