Green synthesis of silver nanoparticles using Sudanese Candida parapsilosis: a sustainable approach to combat antimicrobial resistance.

Background: Antimicrobial resistance (AMR) is a critical global health challenge, particularly in Sudan, where the overuse and misuse of antibiotics have driven the rise of multidrug-resistant (MDR) pathogens. Conventional antimicrobial strategies often fall short due to rapid resistance development and limited efficacy, highlighting the need for novel approaches. Nanotechnology offers promising alternatives, with silver nanoparticles (AgNPs) demonstrating potent broad-spectrum antimicrobial activity. This study aims to develop an eco-friendly synthesis of AgNPs using Candida parapsilosis (C. parapsilosis), an untapped yeast strain isolated from Sudanese soil, to combat AMR.

Results: Biosynthesis of AgNPs using C. parapsilosis was successfully confirmed through UV-Vis spectroscopy, X-ray diffraction (XRD), and high-resolution transmission electron microscopy (HRTEM), revealing well-defined nanoparticles. The biosynthesized AgNPs exhibited strong antibacterial activity against both ATCC reference strains and MDR clinical isolates of Gram-positive and Gram-negative bacteria, with inhibition zones increasing in a concentration-dependent manner. At optimal concentrations, inhibition zones reached 29 mm for Pseudomonas aeruginosa (P.aeruginosa) (ATCC 27853), while clinical isolates of Salmonella typhi (S. typhi) (24.5 ± 0.58 mm) and Escherichia coli (E. coli) (23.8 ± 0.79 mm) exhibited significant susceptibility. Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) assays demonstrated potent bactericidal activity, particularly against E. coli and Klebsiella pneumoniae (K. pneumoniae) at 0.3125 mg/mL. Furthermore, AgNPs synergistically enhanced the efficacy of conventional antibiotics in a species- and antibiotic-dependent manner. The strongest synergy was observed in Enterococcus faecalis (E. faecalis) (up to 9.84-fold with Colistin) and Acinetobacter baumannii (A. baumannii) (up to 5.11-fold with Ceftazidime), suggesting that AgNP-enhanced antibiotic efficacy varies depending on bacterial species, nanoparticle synthesis method, and antibiotic type.

Conclusions: This study presents a novel and sustainable approach to tackling AMR by leveraging Sudanese yeast strains for the green synthesis of AgNPs. The findings underscore the potential of AgNPs as an effective antibacterial agent, both independently and in combination with conventional antibiotics, to combat MDR pathogens. By integrating microbiology and nanotechnology, this research offers a cost-effective and environmentally friendly solution for AMR mitigation. These findings provide a strong foundation for future clinical applications and public health interventions, particularly in resource-limited settings.