The effect of urinary Foley catheter substrate material on the antimicrobial potential of calixerene-based molecules

This study was to investigate the antimicrobial activity of a modified calixarene polymer bound to a silicone substrate in the presence of pathogens associated with catheter infections, Escherichia coli and Proteus mirabilis.

The molecule and its constituent parts were studied bound and unbound to silicone substrates to ascertain growth effects. Minimum inhibitory and bactericidal concentrations were determined against E. coli and P. mirabilis. Biofilm growth was studied by immersing silicone discs seeded with either P. mirabilis or E. coli in artificial urine. Biofilms were assessed at 3, 7 and 10 days. The coated material reduced bacterial cell density compared to the uncoated samples. Direct and indirect toxicity tests were conducted with a fibroblast cell line (3T3); coated and noncoated silicone samples were seeded with cells (1 × 10⁴ /cm² ) and incubated for 72 h. Hoechst propidium iodide staining identified delayed toxic effect from the coated and noncoated material leachate in all but the platinum-cured medical-grade silicone, which showed no evident toxicity.

The calixerene polymer was determined to be the active part of the coating. Biofilm formation was dramatically reduced in the coated platinum-cured medical-grade silicone samples, but cell viability was reduced on the clinical-grade silicones regardless of coating in contrast to cells seeded on the platinum-cured medical-grade silicone. A delayed toxic response was evident to the extract of the coated and noncoated clinical-grade samples, indicating that the toxic effect is due to the underlying substrate.

This study has established that the immobilized molecule enhances the antibacterial and antifouling properties of silicone, without toxicity. It also clearly demonstrates that regardless of coating efficacy, the substrate material has the capacity to disrupt its potency and change the nature of the material coating.