Antimicrobial peptides for detection of bacteria in biosensor assays

Bacteria, plants, and higher and lower animals have evolved an innate immune system as a first line of defense against microbial invasion. Some of these organisms produce antimicrobial peptides (AMPs) as a part of this chemical immune system. AMPs exert their antimicrobial activity by binding to components of the microbe's surface and disrupting the membrane. The overall goal of this study was to apply the AMP magainin I as a recognition element for Escherichia coli O157:H7 and Salmonella typhimurium detection on an array-based biosensor. We immobilized magainin I on silanized glass slides using biotin-avidin chemistry, as well as through direct covalent attachment. Cy5-labeled, heat-killed cells were used to demonstrate that the immobilized magainin I can bind Salmonella with detection limits similar to analogous antibody-based assays. Detection limits for E. coli were higher than in analogous antibody-based assays, but it is expected that other AMPs may possess higher affinities for this target. The results showed that both specific and nonspecific binding strongly depend on the method used for peptide immobilization. Direct attachment of magainin to the substrate surface not only decreased nonspecific cell binding but also resulted in improved detection limits for both Salmonella and E. coli.