Membrane Insertion for Direct Detection of Lipoteichoic Acid

The incorrect diagnosis of bacterial pathogens results in the misuse of antibiotics, a major contributor to the evolution of antibiotic resistance. The ability to rapidly identify a pathogen could facilitate more effective treatment strategies, reducing the unnecessary use of antibiotics. Current diagnostics of bacterial infections often require cell growth, and are therefore less capable of informing timely treatment options. Here, we describe the development of a rapid assay (<45 min) to identify Gram-positive bacteria directly in human serum without any growth or isolation required. We have developed a fluorescence-based immunoassay specifically targeting the Gram-positive bacterial biomarker lipoteichoic acid (LTA). LTA is an amphiphilic molecule with both hydrophobic and hydrophilic portions. Our approach, termed membrane insertion, exploits the amphiphilic biochemistry of the molecule by allowing it to passively insert itself into a lipid bilayer, thereby trapping it for subsequent probing with a fluorescently labeled α -LTA antibody. Using this assay, we have successfully detected less than 10 µ g/ml of LTA directly in spiked human serum. We intend to combine this rapid assay with others currently in development into a diagnostic tool for point-of-care detection of bacterial pathogens.