Exploring the Synergistic Effects of Plant Extracts and Silver Nanoparticles Against Colistin-Resistant Pseudomonas aeruginosa Isolates.

Background: Pseudomonas aeruginosa is a significant nosocomial infection. Since metal nanoparticles (NPs) and plant extracts have demonstrated antibacterial efficacy against multidrug-resistant bacteria, this study aimed to determine the synergistic antibacterial effect of silver nanoparticles and Urtica and Zataria multiflora (Shirazi thyme) extracts against colistin-resistant P. aeruginosa isolated from hospital patients. Materials and Methods: During this cross-sectional study conducted at Isfahan University of Medical Sciences during 2022-2023, a total of 95 P. aeruginosa isolates were collected from selected teaching hospitals in Isfahan province. The Kirby-Bauer disk diffusion method used for antibiotic susceptibility and determining the minimum inhibitory concentration of colistin was checked by microdilution broth, and the presence of the mcr-1 gene was detected by the PCR method. The effect of synergism of Zataria multiflora (Shirazi thyme) and Urtica extracts with silver nanoparticles was investigated by the checkerboard procedure. Results: The screening for antibiotic resistance showed 99% resistance to Levofloxacin and 6% resistance to colistin antibiotic. One isolate is positive for the mcr-1 gene. Furthermore, the combination of Zataria multiflora (Shirazi thyme) and the silver nanoparticles was effective against colistin-resistant P. aeruginosa. Conclusion: For the first time and with the efforts of the colleagues of this study, the synergistic effect of Zataria multiflora (Shirazi thyme) and Urtica extracts and silver nanoparticle extracts against colistin-resistant P. aeruginosa was examined. So, plant extracts and silver nanoparticles might assist with managing multidrug-resistant pathogenic bacteria and be a possible source of medicinal application due to their potential antibacterial effect.