The common oral parasitic protozoan Entamoeba gingivalis forms cysts in response to antibiotic treatment

The eukaryotic protozoan Entamoeba gingivalis (E.g.) is strongly associated with inflamed periodontal pockets. Unlike other obligate anaerobic Entamoeba species, it is considered to not have a life cycle of actively dividing trophozoites and dormant cysts. Accordingly, it has been regarded as non-infectious. To investigate if E.g is capable of encystation in response to adverse environmental conditions, we cultivated clinical isolates of E.g. collected from inflamed periodontal pockets in antibiotics for 8 days. The cytomorphological and ultrastructure forms of the amoeba were investigated by transmission and scanning electron microscopy to reveal cyst formation. We observed exocysts and the encapsulated trophozoids separated by an intra-cystic space, a dense poorly vesiculated cytoplasma and polygonal surface areas of cysts. The cysts walls were composed of chitin. Cysts were conspicuously smaller compared to trophozoids and lacked pseudo- and filipodia. We did not observe multi-nucleated trophozoids after antibiotic induces encystation. Cyst formation in E.g may explain why established treatment approaches often do not stop periodontal tissue destruction during periodontitis and periimplantitis.