Protein antimicrobial barriers to bacterial adhesion

The ability of microorganisms to adhere to solid surfaces is a problem of high visibility and has been the focus of numerous investigations because these organisms can cause disease and food spoilage. During the last several years, considerable attention has been focused on the development of food-grade antimicrobial barriers to adhesion in order to inhibit the initial adhesion of microbial contaminants by application of an antimicrobial agent to the surface rather than trying to remove these contaminants once they are adhered. The premise is that, if both the presence of the agent and its antimicrobial activity are maintained at the interface, sensitive bacterial cells or spores that attempt to attach would be killed. Nisin has been used in foods as a direct additive to inhibit the growth of Gram-positive cells and spores. Similarly, hen lysozyme is a commercially available antimicrobial protein that offers application in food processing systems, but the mode of action of this enzyme differs from that of nisin. We have shown that nisin can adsorb to surfaces, maintain activity, and kill cells that have adhered. In addition, we have addressed questions relating to the short- and long-term stability of adsorbed nisin, the degree to which immobilized nisin can resist exchange with dissolved solution components, and the surface concentrations that are necessary to inhibit biofilm formation. More recently, we have focused on basic questions relating to molecular influences on antimicrobial activity at interfaces using synthetic mutants of bacteriophage T4 lysozyme and hen lysozyme in addition to nisin.