AgNPs biosynthesized from Pseudomonas Z9.3 metabolites as antimicrobial agents against bacterial and fungal pathogens

Two optimal conditions were identified: 37°C, pH 9, and a 5:1 ratio of bacterial supernatant to 5 mM AgNO₃ (S1-9), and 37°C, pH 7, with a 2:4 ratio (S4-7). The UV-visible spectroscopy results showed an absorption range between 400 and 450 nm, confirming the formation of AgNPs. The SEM and TEM analysis showed the spherical shape of AgNPs with a good distribution of nanoparticles and the average size ranged from 8.24 ± 0.26 to 13.32 ± 0.4 nm. Antibacterial activity against different pathogenic bacteria and fungi was tested. Antibacterial activity of AgNPs against six human pathogens and three phytopathogens was evaluated. The antibacterial potential of S1-9 against Gram-negative strains was lower than against Gram-positive strains; in particular, <i>S. epidermidis</i> was the most sensitive (93.76%) compared to the equivalent concentration of Ag. In the case of fungi, S4-7 exhibited better inhibitory activity compared to the negative control. The highest dose (120 ppm) of S4-7 AgNP inhibited fungal growth being the most sensitive <i>Alternaria</i> sp. (74.97%), followed by <i>Stemphylium</i> sp. (66.30%), <i>Fusarium</i> sp. (45.62%), and <i>Rhizopus</i> sp. (32.68%). These findings highlight the potential of synthesized AgNPs as antimicrobial agents for both bacterial and fungal pathogens.