Distribution of internalin gene profiles of Listeria monocytogenes isolates from different sources associated with phylogenetic lineages

Listeria monocytogenes is a human foodborne pathogen with a broad range of hosts. While the L. monocytogenes genome encodes a number of internalins, which are leucine-rich repeat bacterial surface proteins with putative or confirmed roles in host cell attachment and invasion, the specific function of many internalins remains unclear. The distribution of 7 internalin genes (inlC, inlC2, inlD, inlE, inlF, inlG, and inlH) in 120 L. monocytogenes isolates from humans, foods, and animals was investigated to determine if the distribution of these proteins differed with respect to source or phylogenetic lineage. Isolates were classified into 6 different profiles based on internalin gene presence or absence, and a phylogeny based on one stress response (sigB) and two housekeeping (gap and prs) genes was used to correlate these profiles with L. monocytogenes phylogenetic lineages. All 69 isolates classified into L. monocytogenes lineage I, which is overrepresented among human disease cases, had the same internalin profile (presence of inlC and the inlC2DE operon). Lineage II (48 isolates), which is common among food and environmental sources, represented 4 internalin gene profiles, with most isolates carrying inlG and inlF in addition to inlC and inlC2DE. Our data indicate that L. monocytogenes isolates show diverse and distinct patterns of internalin gene presence/absence and L. monocytogenes internalin profiles are associated with phylogenetic lineages.