Vancomycin-functionalized magnetic bead-qPCR platform for rapid differentiation of viable and dead Listeria monocytogenes in food samples

Abstract

The present study reports a dual-functional platform that couples vancomycin-functionalized magnetic beads (VMBs) with real-time quantitative polymerase chain reaction (qPCR) to achieve rapid, culture-free discrimination and quantification of live and dead Listeria monocytogenes in complex food matrices. The exploitation of vancomycin's high-affinity binding to the D-Ala–D-Ala motif of intact peptidoglycan enables the selective capture and removal of viable cells, thereby leaving only DNA from non-viable bacteria for SYBR Green qPCR analysis. Optimisation of bead coupling and adsorption kinetics, in conjunction with a pre-calibrated live/dead correction algorithm, yields an LOD of 10² CFU/mL over a 10¹–10⁷ CFU/mL linear range and completes within 12 h—a process that is significantly faster than conventional culture methods. The validation of the method in beef, salad, cheese, and salmon matrices has yielded recoveries ranging from 96.4 to 99.2 %, with RSDs consistently below 3.6 %. Stability tests have further confirmed that dead-cell DNA remains amplifiable for a minimum of one week, and non-specific capture remains below 5 %. In contrast to isothermal or immunomagnetic approaches, the VMB-qPCR system offers a unique capability to provide unambiguous live/dead resolution without the use of photoactive dyes or extended enrichment, thereby providing a robust, high-throughput tool for food safety surveillance and clinical pathogen monitoring.