Blastocystis

MICROBIOLOGY

• Parasite commonly found in the intestinal flora of humans. Molecular studies have documented numerous genotypes including usually zoonotic organisms, so B. hominis infection is humans is likely more heterogeneous than suspect.
• Global presence, found also in animals e.g., swine.
• Appears as thick-walled cyst (6-40 μm) in human feces [Fig].
• Taxonomic classification unclear. Based on RNA molecular analysis, B. hominis has been labeled as a stramenopile, similar to a large grouping of one and multi-celled protists such as algae, diatoms and slime molds.
  • B. hominis historically used to denote infection but likely more diverse group of Blastocystis causes human infection.
  • Suggest due to diversity, probably refer to Blastocystis spp. or Blastocystis spp. subtype n (n= subtype number, Stensvold classification).
• Life cycle not clearly known, likely transmission through fecal-oral routes, with contaminated water a high suspect. Cysts may infect epithelial cells of GI tract.