Plague ecology is importantly characterized by sporadic epizootics, followed by periods of cryptic dormancy prior to subsequent outbreaks. Recent evidence suggests local persistence of Yersinia pestis bacteria in unidentified reservoirs. Further, the ability of environmentally ubiquitous amoebae to act as permissive hosts to a wealth of competent intracellular pathogens is of growing interest to disease ecologists and One-Health research. Here, we performed environmental genetic surveys and laboratory infection experiments to identify potential mechanisms explaining inter-epizootic plague persistence.
We demonstrate: (1) Y. pestis is an amoeba-resistant microorganism, (2) Y. pestis survives and replicates intracellularly within Dictyostelium discoideum amoebae for at least 48h post infection, (3) Y. pestis is transiently amoeba resistant in four other cyst forming amoeba species, and (4) Y. pestis resides within amoeba structures visually synonymous to those found in infected human macrophages, for which Y. pestis is a competent intracellular pathogen. These results encourage ongoing research into the reservoir potential of amoebae and their shared infection-permissiveness with phagocytic macrophages. Evidence for the existence of plague reservoirs and these newly identified amoeba-resistance phenotypes in Y. pestis stress the importance of recognizing pathogen harboring amoebae as potential threats to global health, agriculture, conservation, and biodefense.