Ojiaku, Adaeze Anne2025-10-092025-10-092025-03Ojiaku, A. A. (2025). The effect of biosynthesized silver nanoparticles in combination with antibiotics on pathogenic microorganisms (Unpublished Doctoral Thesis). Federal University of Technology, Owerri Nigeria .https://repository.futo.edu.ng/handle/20.500.14562/2212Doctoral degree on pathogenic microorganisms. It contains tables, diagrams and pictures.Antimicrobial resistance (AMR) is an emerging chronic public health issue globally, with the prediction of 10 million deaths per year globally by 2050. In this study, silver nanoparticles synthesized using Dacryodes edulis (African pear tree) leaf extract was used in combination with antibiotics and its effects in combination was observed against model gram positive and gram negative microorganisms. Phytochemical constituents of the plant extract, molecular characterization of the microorganisms, biosynthesized silver nanoparticles were characterized, while biosynthesized silver nanoparticles in combination with antibiotics were assessed against the clinically obtained microorganisms. Results revealed presence of alkaloids, tannins, cyanogenic glycosides, flavonoids and anthraquinones. The formation of the silver nanoparticles was established using UV- visible spectrophotometric analysis, exhibiting a characteristic surface plasmon resonance (SPR) band of 390 – 440 nm. Optimization parameters such as extract volume, temperature, and pH revealed 30 ml, 35 oC, and pH 7 as results for optimal nanoparticle synthesis respectively. The reaction time, however, showed a cascade of intensity from the nucleation phase to the stabilization phase with 90 minutes as optimal time for nanoparticle synthesis. XRD analysis showed face centered cubic crystal nature of the lattices with spectral peaks at 38.17, 43.63 and 64.39 corresponding to (111), (200), and (220) plane, with crystallite size of 16.50±0.79 nm using Scherrer equation. Scanning electron microscope (SEM) analysis displayed spherical shaped nanoparticles with average particle size of approximately 63 nm, while Fourier Transform Infrared Spectroscopy (FTIR) analysis acknowledged the presence of functional groups such as phenolic, carboxylic, alkyl, isothiocyanate, and amine groups corresponding to the phytochemical constituents in the aqueous leaf extract being responsible for the bioreduction of silver ions to silver atoms. The microorganisms were identified as Staphylococcus saprophyticus and Escherichia coli. In silico analysis revealed the presence of resistant genes and predicted chromosomal gene mutations especially for E.coli that mediated antimicrobial resistance. Antibiotic assay indicated that in S. saprophyticus, enhanced inhibition was observed for pefloxacin, ampiclox, ciprofloxacin, streptomycin, cotrimoxazole and erythromycin, while reduced inhibition was observed for gentamycin and rocephin. In comparison with antibiotics alone, and antibiotics in combination with AgNPs, gentamycin and rocephin (ceftriaxone) had a reduced zone of inhibition when combined with AgNPs while the other antibiotics had improved zone of inhibition. For E. coli, there was enhanced inhibition for streptomycin, ofloxacin, pefloxacin, amoxicillin, ciprofloxacin, sparfloxacin and chloramphenicol when exposed to antibiotics, while reduced inhibition was noted for cotrimoxazole and gentamycin. However, in comparison with antibiotics alone and antibiotics in combination with silver nanoparticles, it showed that cotrimoxazole and gentamycin had reduced zone of inhibition when AgNPs were added while other antibiotics had improved zone of inhibition in combination with AgNPs. It is recommended that more research on evolutionary associations of microorganisms and antibiotics be performed and also be included in strategies for antibiotic resistance pipeline development and ‘One Health’ approach in combatting antimicrobial resistanceenAttribution-NonCommercial-NoDerivatives 4.0 InternationalDacryodes edulissilver nanoparticlesantimicrobial resistancenanotechnologyantibioticssynergistic InteractionDoctoral Thesis