The present disclosure relates to the isolation of a novel reagent selected for its binding characteristics to the proteins internalin B or internalin A. InIB is a surface-localized protein of Listeria monocytogenes that binds and activates the receptor tyrosine kinase Met. InIB promotes invasion of a number of cells including hepatocytes, endothelial and epithelial cell lines and causes activation of the actin-mediated internalization of the bacterium. InIA belongs to a large group of surface-localized leucine-rich repeat (LRR) proteins identified in the Listeria genome. InIA enables Listeria monocytogenes to invade non-phagocytic cells such as those of the human intestinal epithelium and is sufficient for adhesion to and inducing uptake into epithelial cells. The disclosed nucleic acid ligands to internalin B and internalin A may be useful for determining the presence or absence of internalin B, internalin A, or Listeria in food, clinical or environmental samples; they may also be useful as an agent for combating Listeria infection by binding to and inactivating the infection-promoting inlB or inlA proteins. One object is to incorporate these nucleic acid ligands into an in vitro diagnostic or biosensor platform designed to detect the presence or absence of internalin B, internalin A, or Listeria in food, clinical or environmental samples. Another object is to employ these nucleic acid ligands in methods for treating or preventing Listeria infection.