R. Jain, A.L. Milkowski, K.P. Nelson, D.A. Busche, D.M. Lynn, C.J. Czuprynski, N.L. Abbott
Bemis Company, Inc.,
Keywords: packaging, antimicrobial, chemotaxis, chemoattractant
Summary:High barrier flexible packaging protects its contents from the external environment by virtue of the physical barrier presented by its multilayer structure. Once the package is sealed, the package wall is impervious to objects in the size regime of microbes (bacteria, viruses, fungi and their spores). While small molecule ingress can occur, the package wall is designed to slow the transport of diffusible species like oxygen and water vapor. Thus, deleterious interactions with the package contents are minimized and their useful life is extended. However, bacteria can be resident on product surfaces prior to packaging. Those bacteria do survive and their growth may reduce the quality and safety of the product. For added protection, post-packaging bacterial growth can be controlled by in-situ sterilization techniques using thermal, radiation or chemical treatments. Alternately, active packaging strategies can be conceived where antimicrobial compounds are incorporated into the package itself.A wide variety of antimicrobial remediations are available that can generate bacteriostatic or bactericidal surfaces. While these bactericidal surfaces usually contain immobilized antimicrobial agents on their surface and are therefore ‘contact killing’ towards microbes in their vicinity, their efficacy is not readily transferrable to the packaged product. That is, even though bacteria cannot thrive on the package, they continue to grow on the packaged contents. To counter this, a microorganism’s chemotactic response to certain chemical compounds was studied to see if it could be exploited and the antimicrobial qualities of a representative surface could be enhanced.Here, we sought to demonstrate that the antimicrobial activity of a contact-killing surface can be enhanced by gradients in the concentration of soluble chemoattractants that attract planktonic bacteria to that surface. We show that two natural and non-biocidal chemoattractants (aspartate and glucose) can be used to attract bacteria to model surfaces decorated with contact-killing quaternary ammonium groups. Our results demonstrate that this approach can kill Escherichia coli and Salmonella typhimurium, two notorious human pathogens, at levels 10- to 20-fold greater than the native surfaces themselves. We conclude that systems designed to draw bacteria toward surfaces can provide a new and useful approach to improving the performance of conventional (passive) contact-killing antimicrobial surfaces. This approach is likely general, and provides new strategies for the design of active or dynamic contact-killing surfaces with enhanced antimicrobial activities.