Case #291 – January, 2011

A state health laboratory sent a formalin-ethyl acetate (FEA) stool concentrate to the DPDx Team for Entamoeba confirmation/identification. Because formalin was used in the preservation and processing of the specimen, PCR could not be employed to rule-out E. histolytica. A wet mount was made and examined microscopically. Figure A shows an object observed in moderate numbers on the wet mount at 1000x magnification. The object measured 12 micrometers in diameter. Figures B–D show the same object but in different focal planes. What is your diagnosis? Based on what criteria?

Figure A

Figure B

Figure C

Figure D

This case showed a mature cyst of Entamoeba coli. Showing the same cyst in four different focal planes clearly demonstrated the presence of more than four nuclei, which is diagnostic for this species. The cyst was also within the size range for E. coli.