Effect of colloidal silver against Ciprofloxacin persisters of Pseudomonas aeruginosa PAO1

Pseudomonas aeruginosa causes chronic multidrugresistant infections, often linked to antibiotic-tolerant persister cells in biofilms. The treatment of such infections poses chemotherapeutic limitations. This study evaluates the efficacy of colloidal silver (SilverSol® technology) against Ciprofloxacintolerant persisters of P. aeruginosa PAO1 in planktonic and biofilm populations. Dose-kill assays showed persister formation at 20×MIC of ciprofloxacin in planktonic cells and 50×MIC in biofilms. Colloidal silver exhibited a MIC of 3ppm for planktonic cultures and 4 ppm for biofilm inhibition. Complete eradication of Ciprofloxacin persisters occurred using colloidal silver at 5×MIC in planktonic cells and 3×MIC in biofilms within 1 hour. Total biofilm eradication was possible at 4 ppm using TTC viability assays. Checkerboard assay revealed an additive effect of ciprofloxacin and colloidal silver (FIC index: 0.65). FESEM imaging and Allison- Sutherland staining confirmed the absence of extracellular matrix, demonstrating biofilm inhibition by the colloidal silver. Hence, these findings highlight colloidal silver as a promising therapeutic strategy against persistent infections caused by ESKAPE pathogens such as P. aeruginosa PAO1.