Response surface methodology approach for optimization of antibacterial activity of silver nanoparticles synthesized using Streptomyces sp. PBD 311B

Aims:The increasing prevalence of antibiotic-resistant bacterial strains has intensified the search for novel antimicrobials.This study aimed to optimize the biosynthesis parameters of silver nanoparticles (AgNPs) produced by Streptomyces sp.PBD 311B to achieve enhanced antibacterial efficacy.Methodology and results: Response Surface Methodology (RSM), a highly accurate prediction method, was applied to optimize the biosynthesis of AgNPs using salt-tolerant actinobacteria, Streptomyces sp.PBD-311B.The most effective variables, such as starvation period, AgNO3 concentration, and incubation duration, were selected to optimize the conditions for the biosynthesis process.AgNPs were characterized, and the antimicrobial activities were determined.The optimum conditions for the biosynthesis of AgNPs were achieved using the variables: bacteria starvation period (72 h), AgNO3 concentration (2 mM), and incubation duration to synthesize AgNPs (84 h).UV-Vis analysis of the synthesized AgNPs revealed the presence of AgNPs at SPR 430 nm.The average size of AgNPs was 30.41 7 nm with a zeta potential of -20.8 mV.Further, the XRD diffraction peak closely aligned with the FCC structure of silver, and FT-IR analysis confirmed the presence of biomolecules coated on the AgNPs surface.Interestingly, the antibacterial activity of AgNPs against Staphlococcus aureus was doubled under optimized conditions.Moreover, AgNPs demonstrated bactericidal effects against Gram-negative bacteria with MIC and MBC values of 31.25 g/mL and 250 g/mL, respectively.However, S. aureus showed higher resistance to AgNPs, with MIC of 125 g/mL and MBC of 500 g/mL, indicating a bacteriostatic effect.Conclusion, significance and impact of study: The findings discovered an optimum condition for AgNPs synthesis using the RSM approach.Consequently, these optimized conditions substantially improved the antimicrobial efficacy against Gram-positive (S. aureus) and Gram-negative bacteria.These findings hold promise for developing more effective antimicrobial agents with broad-spectrum activity.