Listeriosis is of major veterinary importance, impacting on animal welfare and its designation as a food-borne pathogen. Over the last 17 years, the percentage of bovine abortions caused by Listeria monocytogenes has increased by 2.9%, with every abortion costing the dairy farmer around £630. L. monocytogenes has particular tropism for the gravid uterus, however, the route of infection of the ruminant placentome is relatively unknown.
The present study investigated the ability of a range of environmental and clinical L. monocytogenes isolates to infect cells of the bovine feto-placental barrier using two cell types: Caco2 (a human colon epithelial cell line used routinely to investigate Listeria pathogenesis) and Bovine Caruncular Epithelial Cells (BCECs, maternal cells of the placental fetal/maternal interface).
All Listeria isolates tested invaded Caco2 and BCEC cells. L. monocytogenes strain differences were only detected in Caco2 cells, however the level of invasion was lower (p<0.0001) for BCEC cells. The majority of infected Caco2 cells contained >10 bacteria (52.3%), whereas the majority of infected BCEC cells had only a single Listeria invading (81.8%). These results demonstrate that Listeria is capable of invading BCEC cells, suggesting that these strains may also be capable of causing listeriosis at the placentome in vivo.