Design of a novel affinity probe using the cell wall-binding domain of a Listeria monocytogenes autolysin for pathogen detection

Abstract

Rapid identification of foods and food-processing environments contaminated with Listeria monocytogenes is crucial for controlling human listeriosis, a leading cause of fatality related to foodborne illnesses. The L. monocytogenes autolysin IspC anchors to the bacterial surface non-covalently via its C-terminal cell wall-binding domain (CWBD), which contains conserved Gly-Trp (GW) dipeptides. This study explored the binding property of CWBDIspC to design an affinity probe for detecting L. monocytogenes. Immunogold electron microscopy analysis of a ∆ispC mutant and its wild type (WT) revealed that exogenously added CWBDIspC bound to surface ligands that were evenly distributed and remained mostly unoccupied in the wild type. CWBDIspC detected, via recognizing the cell wall component lipoteichoic acid, L. monocytogenes strains primarily belonging to the serotype 4 group, as well as Listeria innocua, and Listeria welshimeri but did not detect three other Listeria spp. (Listeria seeligeri, Listeria ivanovii, and Listeria grayi) nor any non-Listeria spp. tested. CWBDIspC, when tagged with the enhanced green fluorescent protein, was capable of detecting L. monocytogenes by fluorescence microscopy, a colony lift filter assay, and a microtube binding assay. CWBDIspC, when covalently attached to magnetic beads, showed the ability to separate L. monocytogenes cells with a maximum capture rate of 90 to nearly 100% from 1 × 103 to 1 × 105 target cells. This study demonstrated for the first time that the CWBD derived from a GW surface protein IspC is a novel antibody alternative for the rapid detection and isolation of L. monocytogenes despite binding to two other Listeria species.