Jess VergisVARSHA UNNI2023-04-052023-04-052022-04-02https://krishikosh.egranth.ac.in/handle/1/5810196074Submitted in partial fulfilment of the requirement for the degree of Master of Veterinary Science in Veterinary Public HealthIn the recent wake of antimicrobial resistance, nanotechnology has received remarkable attention and has been considered as a promising interventional tool for treating the drug resistant pathogens. The present study evaluated the antibacterial efficacy of green synthesised Zinc Oxide nanoparticles (ZnO NPs) against multi-drug resistant non-typhoidal Salmonella spp. (MDR-NTS). The synthesis and characterisation of ZnO NPs was attempted using the aqueous extract of Piper longum catkin. Initially, the characterisation of green synthesised ZnO NPs was performed by UV- Vis spectroscopy, Fourier transform infra- red spectroscopy (FTIR), Thermogravimetric analysis (TGA) and differential thermogravimetric analysis (DTA), powder X-ray diffraction (PXRD), Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM). The green synthesised ZnO NPs exhibited an absorbance peak at 340 nm by UV- Vis spectroscopy, which was confirmed by FTIR analysis. The TGA/DTA revealed a progressive thermal degradation of the ZnO NPs between 250oC and 400oC, however, a good thermal stability was exhibited for annealing temperatures between 900oC and 1300oC. The ZnO NPs exhibited a hexagonal wurtzite crystalline structure by PXRD analysis, which was further confirmed by SEM and TEM. This study evaluated the in vitro antibacterial efficacy of ZnO NPs against MDR- NTS strains (S. enterica Typhimurium and S. Enteritidis (n= 3 for each serotype). The minimum inhibitory concentration (MIC; 125 μg/ml) and minimum bactericidal concentration (MBC; 250 μg/ml) of ZnO NPs was determined by employing microbroth dilution technique. Later, ZnO NPs was also tested for its stability (high- end temperatures, physiological concentration of cationic salts, proteases and pH); safety (chicken RBCs; HEK cell lines) and effect on gut beneficial lactobacilli (Lactobacillus acidophilus and L. plantarum). In general, the ZnO NPs tested stable at MIC concentration; however, a three to four- fold rise in the MBC value was observed. Besides, ZnO NPs were tested safe with chicken RBCs and HEK cell lines at MIC (1X, 2X, 5X and 10X) levels; moreover, the beneficial gut lactobacilli were not inhibited. Furthermore, the in vitro time- kill kinetic assay of MDR-NTS strains treated with ZnO NPs revealed a complete clearance after 360 min. To conclude, the biosynthesised ZnO NPs was found to exhibit antibacterial activity against the tested MDR-NTS, found stable and safe. Overall, the study demonstrated facile, eco- friendly method for the synthesis of ZnO NPs, which could be employed as a potential antimicrobial alternative candidate.EnglishThesis