Nisin/polyanion layer-by-layer films exhibiting different mechanisms in antimicrobial efficacy

Nisin/polyanion Layer-by-Layer (LbL) films are reported to exhibit different mechanisms in antimicrobial efficacy depending on the type of polyanion. LbL films consisting of nisin as the polycationic component were prepared using two different polyanionic constituents: poly acrylic acid (PAA) and dextran sulfate (DX). Due to the weaker interaction strength of carboxylate groups with nisin compared to sulfate/nisin, a larger molecular weight of PAA was needed to achieve LbL assembly. PAA-100K/nisin and DX-15K/nisin multilayer films exhibited significantly different properties. PAA-nisin films grew faster compared to DX-nisin films and showed, for 60 bilayer films, an average bilayer thickness of 21.6 nm compared to that of 6.1 nm in DX-nisin films. The total amount of nisin was found to be 17.1 ± 2.2 μg cm^-2 in (PAA-nisin)₆₀ and 6.8 ± 0.4 μg cm^-2 in (DX-nisin)₆₀ films. The stability of the films was investigated at three different pH values of 6.0, 7.4 and 9.5. (PAA-nisin)₆₀ films exhibited the release of nisin into the solution which resulted in the disintegration of the film over several hours. A burst release was observed in the first hour followed by a slower release and disintegration over 24 hours with a complete release at pH 9.5. The bacterial growth inhibition test against Staphylococcus epidermidis confirmed the antimicrobial activity of nisin released from PAA-nisin films. PAA was found to stabilize nisin and the film-released nisin retained its antimicrobial activity in the neutral and alkaline pH values. Unlike PAA-nisin films, (DX-nisin)₆₀ films were stable at the physiological conditions up to 14 days with no release of nisin. DX-nisin films were found to inhibit the attachment of Staphylococcus epidermidis and prevent biofilm formation. These results clearly demonstrate the effect of different polyanions on nisin LbL films to achieve different mechanisms in antimicrobial efficacy and show the potential of PAA-nisin multilayer films as promising local delivery systems for treatment of burns and wounds, while DX-nisin multilayer films can be employed as stable coatings against bacterial attachment and biofilm formation.