Recapitulating the life cycle of the global pathogenEntamoebain mice

Abstract

There are several Entamoeba species that colonize humans, but only Entamoeba histolytica causes severe disease. E. histolytica is transmitted through the fecal-oral route to colonize the intestinal tract of 50 million people worldwide. The current mouse model to study E. histolytica intestinal infection directly delivers the parasite into the surgically exposed cecum, which circumvents the natural route of infection and does not produce infectious cysts. To develop a fecal-oral mouse model, we screened our vivarium for a natural murine Entamoeba colonizer via a pan-Entamoeba PCR targeting the 18S ribosomal gene. We determined that C57BL/6 mice were chronically colonized by Entamoeba muris. This amoeba is closely related to E. histolytica, as determined by 18S sequencing and cross-reactivity with an E. histolytica-specific antibody. In contrast, outbred Swiss Webster (SW) mice were not chronically colonized by E. muris. We orally challenged SW mice with 1x105E. muris cysts and discovered they were susceptible to infection, with peak cyst shedding occurring between 5-7 days post-infection. Most infected SW mice did not lose weight significantly but trended toward decreased weight gain throughout the experiment when compared to mock-infected controls. Infected mice treated with paromomycin, an antibiotic used against non-invasive intestinal disease, do not become colonized by E. muris. Within the intestinal tract, E. muris localizes exclusively to the cecum and colon. Purified E. muris cysts treated with bovine bile in vitro excyst into mobile, pre-trophozoite stages. Overall, this work describes a novel fecal-oral mouse model for the important global pathogen E. histolytica.