Bacterial membranes are the target for antimicrobial polysiloxane-methacrylate copolymer

Antibacterial polysiloxane polymers with pending tert-butylamine groups are a novel class of compounds that are compatible with silicone elastomers, but their mechanism of action is not well understood. The research into their action mechanism was conducted on a polysiloxane copolymer grafted with tert-butylaminoethyl methacrylate and covalently attached fluorescein. Fluorometric measurements results suggest that the polymer forms a stable link with bacteria. The results of β-galactosidase enzyme assay with the use of ortho-nitrophenyl-β-galactoside as a substrate show that the polymer has a damaging effect on bacterial membranes. The scanning and transmission electron micrographs of Escherichia coli cells incubated with the polymer prove further that the polymer's site of action is bacterial cell membranes. In order to investigate the polymer interaction with bacterial membranes the fluorescein labelled polymer was incubated with bacterial cells and membranes isolation and identification method was next applied. The E. coli membrane fractions were identified by light scattering, protein content, oxidase NADH activity and N-phenylnaphtylamine fluorescence measurements, as well as electron microscopy. Oxidase NADH and N-phenylnaphtylamine were the inner membrane markers. The bacterial membranes were then tested for the presence of the polymer. The experiments gave evidence that the copolymer binds to the inner bacterial membrane. Further studies, where the copolymer was incubated with isolated mixed (inner and outer) membrane fractions, proved that the copolymer exerts more destructive effect on E. coli outer membrane. The damaging effect on the membranes is concentration dependent.