Polydimethylsiloxane loaded capsaicin afflicts membrane integrity, metabolic activity and biofilm formation of nosocomial pathogens

Biofilms constitute 80 % of all nosocomial infections associated with invasive medical devices. Polydimethylsiloxane, a highly elastic, inert, non-reactive, biocompatible silicone polymer is widely used as implant biomaterial due to its non-toxic and low-immunogenic nature. Owing to its hydrophobicity, PDMS suffers from microbial adhesion. Inhibition of biofilm formation on PDMS surfaces is imperative to prevent morbidity, mortality and replacement of implants. The present study investigates the efficacy of capsaicin (0.5 % w/v) loaded PDMS as a broad spectrum antimicrobial surface against Staphylococcus aureus, Escherichia coli and Candida albicans. Capsaicin exhibited minimum inhibitory concentration of 1024 μg mL^-1 for S. aureus, E. coli and 256 μg mL^-1 for C. albicans. Capsaicin inhibited biofilms of S. aureus, E. coli and C. albicans at much lower concentrations of 2, 64 and 8 μg mL^-1 respectively. The minimum capsaicin concentrations required for total biofilm eradication was found to be 256, 512, 128 μg mL^-1 for S. aureus, E. coli and C. albicans respectively. Probing sub-lethal concentrations of capsaicin revealed 38, 32, 30 % reduction in metabolic activity of S. aureus, E. coli & C. albicans planktonic cells respectively. Similarly, there was an increase in permeability of cells to propidium iodide compared to control. By reducing the metabolic activity and perturbing membrane integrity, capsaicin could prevent biofilm formation and this was also observed with capsaicin-PDMS surfaces that exhibited 1 log (∼90 %) reduction of viable bacterial counts.