Title

The Impact of Surfactants and Polymer Dispersion Components On Antimicrobials

Date of Award

2006

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Polymers and High Performance Materials

First Advisor

Douglas A. Wicks

Advisor Department

Polymers and High Performance Materials

Abstract

Antimicrobial oligopeptides are potent natural biocides. Application of such peptides as an alternative to problematic small molecule biocides in polymer coatings is a new and relatively untapped area of research. To successfully incorporate these in commercial polymer coatings, the solution properties of the antimicrobial peptide/polymer coatings component mixtures and the fundamental interactions that dictate peptide antimicrobial activity were investigated. This research addressed the aforementioned via three independent but supporting phases of research. The first phase of this research determined relationships that exist between dispersion components (surfactant, hydroxyethyl cellulose, and trace elements) and the viability of P. aeruginosa in solution. The importance of surfactant chemical structure was evaluated via a series of ethoxylated nonyl phenols (ENPs). It was found that bacteria viability in solution is promoted by the ionic nature of the surfactant and trace elements typically found as impurities in industrial water. The second phase of this research employed fluorescence techniques and traditional microbiological methods to determine that polymer coatings components impact the efficacy of small molecule biocides. Specifically, it was determined that the charged endgroup of the surfactants and surfactant counterion were critical to interactions that yield the observed changes in biocide efficacy. The final phase of this research investigated the solution and antimicrobial properties of the antimicrobial peptide Ac-RRW WRF-NH2 (Combi1). Combi1 formed aggregates in aqueous solution; however, in surfactant solution the aggregates were broken down. Fluorescence spectroscopy and NMR studies indicate that the peptide locateed within the palisade layer of nonionic ENP micelles. Properties of the peptide aggregate were dependent on time, concentration, and pH. Characteristics of the peptide aggregate are important to the antimicrobial efficacy expressed in solution. For example, the efficacy of the peptide against E. coli bacteria in nonionic surfactant solution mixtures is correlated with the concentration of the peptide stock solution, as well as the final peptide:surfactant ratio. From these results it is theorized that the peptide aggregate interacts with bacteria in solution. This suggests that the current theory of peptide molecules existing singularly in solution and aggregate after initial interaction with the bacteria membrane surface is incomplete, and that a revised model is needed.