The Application of <i>Spirulina platensis</i>-Based Green Synthesized Silver Nanoparticles Demonstrating Potent Anti-<i>Shigella flexneri</i> Effects

Background: The emergence of antibiotic-resistant strains of Shigella flexneri, an important cause of Shigellosis, has led to extensive research to find alternative treatment approaches. Therefore, the current study investigated the antibacterial effects of the green synthesized silver nanoparticles (AgNPs) using Spirulina platensis on S. flexneri and the expression of pathogenic genes ipaB, ipaD, ipaH, and qnrS. Methods: After synthesizing AgNPs using S. platensis, its antibacterial effects on S. flexneri were studied using the microdilution method with 96-well plates. In addition, to determine the minimum bactericidal concentration (MBC), 10 µL of the contents of the minimum inhibitory concentration (MIC) well and the like were swapped on the nutrient agar medium. After RNA extraction, complementary DNA (cDNA) synthesis, and primer design, the expression levels of ipaB, ipaD, ipaH, and qnrS genes were evaluated using the real-time polymerase chain reaction (PCR) technique. The data were analyzed by GraphPad Prism 8. Results: The MIC of the green synthesized AgNPs was measured as 0.0625 μg/mL, and its MBC was 0.125 μg/mL. The results of RT-PCR analysis indicated a significant decrease in the expression levels of pathogenic genes ipaB, ipaD, ipaH, and qnrS in AgNP-treated S. flexneri. Conclusion: The green synthesized AgNPs using S. platensis had strong antibacterial effects on S. flexneri, and the action mechanism was attributed to the downregulations of ipaB, ipaD, ipaH, and qnrS genes. In vivo and clinical studies are needed in this respect.