Investigation of Synergism of Silver Nanoparticle and Erythromycin Inhibition and Detection of Exotoxin-A Gene in Pseudomonas aeruginosa Isolated from Burn Wounds Secretion

 Pseudomonas aeruginosa infections are resistant to antimicrobial agents and produce toxic virulence factors such as exotoxin A. Studies have shown that some nanoparticle compounds and antibiotics have a synergistic effect. Therefore, the aim of this study was to investigate the synergistic effect of silver nanoparticles and erythromycin on antibiotic-resistant P. aeruginosa.

 In this descriptive cross-sectional study, 40 cultured samples of burn wound secretions were taken from Imam Musa Kazem (PBUH) Burns Hospital in Isfahan, Iran. Diagnostic and differential tests were performed. Antibiogram was performed to obtain the bacterial resistance pattern and the exotoxin A gene was detected by PCR. The bacterial minimum inhibitory concentration (MIC) was then applied to the silver nanoparticles (shape and mean size) and erythromycin separately and a common mixture of both in 10 dilutions to investigate the synergistic effect.

   A number of 26 bacteria were strains of P. aeruginosa. Of samples, 25 (96.15%) had exotoxin A gene. All samples were sensitive to all erythromycin concentrations. The mean MIC of nanoparticles against bacteria was reported to be 2 μg/mL. A solution of 40 μg/mL erythromycin and 2 μg/mL nanoparticles was also considered as MIC solution. Pseudomonas aeruginosa is sensitive to erythromycin to very low concentrations of silver particles. But no synergistic effect between silver nanoparticles and erythromycin was reported for this bacterium. Based on PCR results and antibiotic resistance pattern, a significant number of the samples contained the exotoxin A gene and the use of erythromycin alone was not appropriate for treatment.