Evidence for subpopulations of Listeria monocytogenes with enhanced invasion of cardiac cells

Cardiac infections caused by the foodborne bacterium Listeria monocytogenes represent a significant but poorly studied facet of disease. It is not known whether L. monocytogenes cardiac infections stem solely from host susceptibility, or whether bacterial isolates exist that exhibit a tropism for cardiac tissue. Here we examine the cardio-invasive capacity of a recent L. monocytogenes cardiac case strain (07PF0776) as well as nine additional outbreak and clinical isolates. Mice infected with the cardiac isolate 07PF0776 had 10-fold more bacteria recovered from heart tissue than those infected with L. monocytogenes strain 10403S, a well-characterized clinical isolate originally obtained from a human skin lesion. Additional L. monocytogenes isolates exhibited varied capacities to colonize the hearts of mice; however, those with the highest efficiency of mouse cardiac invasion also demonstrated the highest levels of bacterial invasion in cultured myoblast cells. Our findings strongly suggest that subpopulations of L. monocytogenes strains have acquired an enhanced ability to target and invade the myocardium.