Cytotoxicity and antibacterial activity of actinomycetes-mediated biogenic silver nanoparticles against methicillin-resistant Staphylococcus aureus (MRSA)

Background: MRSA is one of the most life-threatening pathogens, thus its prevention has become a crucial public health concern. Objectives: This study aims to determine the prevalence of MRSA among coagulase-positive staphylococci and evaluate the cytotoxicity and anti-MRSA efficacy of biogenic silver nanoparticles (AgNPs). Methodology: Phenotypic detection of MRSA among 220 coagulase-positive Staphylococcus spp. isolates was investigated by CHROMagar™ MRSA, and their identification was confirmed by MALDI-TOF and detection of nuc and mecA genes. Furthermore, the actinomycetes-mediated biosynthesized AgNPs were characterized, and their cytotoxicity and anti-MRSA potential were assessed. Results: Of 220 isolates, 92 (41.8%) were presumptively identified as MRSA by CHROMagar MRSA, however, MALDI-TOF discriminated them into S. aureus, S. pseudintermedius, S. cornubiensis, and S. delphini. Results of molecular characterization revealed the presence of nuc and mecA genes in all confirmed MRSA isolates. In addition, a promising AgNPs-producing Streptomyces virginiae SNPPA6 was isolated, identified and utilized for extracellular biosynthesis of spherical AgNPs with an average size of 11.18 nm. The characterization of the AgNPs by XRD and FTIR revealed their crystalline nature and the presence of proteinaceous capping agents. The biogenic AgNPs exhibited promising anti-MRSA activity with MIC values ranging from 4 to 64 µg/mL. Cytotoxicity assessments using MTT assay indicated the cytotoxic impact of AgNPs on MDA-MB-231, A549 and HSF cell lines with IC50 values of 24.5, 29.2 and 36.3 µg/mL, respectively. Conclusion: Our findings highlighted the potential application of the biogenic AgNPs produced by S. virginiae SNPPA6 as a promising candidate for fighting MRSA at non-cytotoxic concentrations.