Listeria monocytogenes is known to also infect and even cause listeriosis in several other vertebrates, including birds and fish, some of which produce additional or different types of lysozymes with different substrate specificity (Miettinen and Wirtanen, 2005; Hellström et al., 2008; Callewaert and Michiels, 2010), and the presence and ability to modulate the activity of different PG modifying enzymes may be an adaptation to this promiscuous lifestyle. This evidence concerns the gene LYZ and listeriosis.