Testing the Durability of Polymyxin B Immobilization on a Polymer Showing Antimicrobial Activity: A Novel Approach with the Ion-Step Method

Abstract

A polymyxin B (PMB) modified copolymer of ethyl acrylate and 2-hydroxyethyl methacrylate is reported that shows antibacterial activity towards E. coli. The polymer is designed for biosensor interfaces to provide protection against microbial contamination. However, leaching of a biomolecule from its solid support is a well-known problem in immobilization chemistry. It has been proposed that antimicrobial activity results from release of the antibiotic from the polymer matrix, but in the work reported here, bactericidal action was seen for tresyl activated polymers even when no polymyxin B could be detected in the supernatant and where covalent attachment of PMB was indicated. Further evidence for the in situ action of PMB on the polymer was provided using a novel method of investigation, subjecting the polymer, deposited on an Ion-Sensitive Field-Effect Transistor (ISFET) to a step change in ion-concentration (Ion-step). With the ion-step method activation of the polymer and the grafting of Polymyxin-B were followed. A comparison of absorbed PMB on a nonactivated polymer and PMB on the tresyl activated polymer suggested that if leaching of PMB from the latter occurred, it was below the detection limit and well below the minimum inhibitory concentration (MIC) for antimicrobial action. Bactericidal action was thus attributed to PMB attached to the polymer.