As a result, this study aims to synthesize and characterize copper nanoparticles using the aqueous extracts of Psidium guajava (leaves combined with fruits) and to conduct antimicrobial tests on clinical resistant isolates of two gram-negative bacteria (Salmonella spp and Escherichia coli) and two gram-positive bacteria (Staphylococcus aureus and Streptococcus spp). Our objective is to perform both acidic and alkaline syntheses of CuNPs and compare their antimicrobial activity on resistant clinical isolates.