Scientific Classification
The appropriate classification of B. hominis remains controversial. Back in 1912, Brumpt described the organism as a harmless yeast due to its yeast-like glistening appearance in fresh wet mounts and the absence of pseudopodia and locomotion. This was then refuted by Zierdt who reclassified it under subphylum Sporozoa based on some distinctive protistan features that the Blastocystis cell has, such as the presence of nuclei, smooth and rough endoplasmic reticulum, Golgi complex, and mitochondrion-like organelles. Its sensitivity to antiprotozoal drugs and its inability to grow on fungal media further indicated that it was a protozoan. However, some revisions were made to the classification system recently based on modern molecular approaches to classification and studies have shown that Blastocystis is neither yeast nor a protozoan. It is placed in a new Class, known as Blastocystea, under the Subphylum Opalinata, Infrakingdom Heterokonta, Subkingdom Chromobiota, Kingdom Chromista (Cavalier-Smith, 1998).