On the identification of some Entamoeba species - response to Ponce-Gordo and Martínez-Díaz.

The authors are entitled to their opinion that we are not justified in attributing the name Entamoeba equi to our horse isolate and can use Entamoeba sp. if they prefer. However, we take issue with their reasoning. Their criticism of our citation comes from a misreading – the citation was for the medium, not the amoeba. Describing the morphology of the culture trophozoites would in any case have been useless as it is well known that trophozoite size in culture need not reflect size in vivo. Species of the genus Colpodella are aerobic organisms while Entamoeba species are anaerobic, so they cannot both derive from contamination. We did not see cysts, but we did show that the small subunit rRNA gene sequence of the Entamoeba clusters strongly with the 4-nucleated cyst clade in phylogenetic trees. Since the sequence represents a distinct lineage with no specific relatives and is from a unique host, and since E. equi is the only valid species name for a 4-nucleated cyst-producing Entamoeba species in horses, we feel justified in using it for this organism.