Guava fruits and leaves contain a high amount of vitamins, tannins, polyphenols, and various compounds, including resin, sugars, triterpenes, essential oil, isoquercitrin, reynoutrin, guajaverin, avicularin, kaempferol, guajanoic acid, saponin, carotenoids, lectins, leucocyanidin, ellagic acid, amritoside, β-sitosterol, uvaol, oleanolic acid, and ursolic acid . Pharmacological research, both in vitro and in vivo, on guava leaves, has demonstrated their potential for co-treating various ailments, including infectious and parasitic diseases, neoplasms, blood and immune system disorders, endocrine and metabolic diseases, circulatory system disorders, digestive system disorders, and skin-related issues. Furthermore, several randomized and clinical trials conducted in the last two decades have explored the effects of guava leaf extract in treating various medical conditions . Shakeela and colleagues have highlighted the pivotal role of pH in nanoparticle (NP) synthesis. They pointed out that higher pH levels lead to the production of smaller NPs, hindering further nucleation, while acidic pH impedes NP formation, and alkaline pH facilitates it . Saliani et al. observed that the inhibitory effects of NPs on bacterial growth are pHdependent, with growth inhibition intensifying as pH decreases from 7 to acidic levels . Given the established antimicrobial activity of Psidium guajava extracts and the pH-dependent microbial growth inhibition, the synthesis of CuNPs at a pH range of 4-5 using these plant extracts emerges as a promising strategy to address challenges associated with antimicrobial resistance (AMR). Notably, there is no existing literature over the past ten years on biosynthesizing copper nanoparticles using Psidium guajava aqueous extract at acidic pH and testing its antimicrobial activity on clinical resistant strains of Salmonella spp, Escherichia coli, Staphylococcus aureus, and Streptococcus spp.