Recherche des Actinomycetota contribuant à la biosynthèse des nanoparticules d’argent pour des applications antimicrobiennes

Abstract

The main objective of this work is to investigate Actinomycetota involved in the biosynthesis of silver nanoparticles (AgNPs) intended for antimicrobial applications. For this purpose, ten Actinomycetota isolates (L1, L2, L3, L4, L5, L6, L7, L8, L9, and L10) were cultured in ISP2 medium. The biosynthesis of AgNPs was carried out using silver nitrate (AgNO3) as a metallic precursor and the Actinomycetota biomass extract as a reducing and stabilizing agent. The obtained nanoparticles were subsequently purified and dried. To optimize their synthesis, several parameters were studied, including AgNO3 concentration, pH, and temperature. The bioreduction of Ag + ions to Ag 0 was evidenced by the color change of the solution to dark brown, observed for strains L1, L3, L4, L6, L7, and L10 during extracellular synthesis, as well as for strains L1 and L4 during intracellular synthesis. This synthesis was also confirmed by UV-Visible spectrophotometric analysis, which revealed characteristic absorption peaks of silver nanoparticles at 340, 355, 365, 390, 400, 425, 440, and 455 nm. Furthermore, the antimicrobial activity of the synthesized AgNPs was evaluated against various pathogenic microorganisms using the agar well diffusion method. For this study, three strains presenting the most characteristic UV-Visible absorption profiles associated with high AgNP production (L3, L6, and L10) were selected. The results showed strong antimicrobial activity against Candida albicans, followed by moderate activity against Staphylococcus aureus and Aspergillus flavus, as well as weak activity against Pseudomonas aeruginosa. Comparative analysis of the different strains revealed significant variability in their antimicrobial efficacy. Strain L3 stood out with the broadest spectrum of action, inhibiting the growth of all tested microorganisms. It recorded the largest zones of inhibition against Candida albicans (20.67 mm), followed by Aspergillus flavus (13.33 mm), Staphylococcus aureus (12 mm), and Pseudomonas aeruginosa (11.33 mm). Strain L10 presented a more selective activity, limited against Candida albicans (19.83 mm) and against the Gram-positive bacterium Staphylococcus aureus (9.33 mm), without any effect on Pseudomonas aeruginosa or Aspergillus flavus. As for strain L6, it presented the lowest activity, acting only on Candida albicans with an inhibition zone of 17.33 mm, while remaining inactive against the other tested microorganisms.