Intra-subtype variation in enteroadhesion accounts for differences in epithelial barrier disruption and is associated with metronidazole resistance in Blastocystis subtype-7

PLoS Negl Trop Dis. 2014 May 22;8(5):e2885. doi: 10.1371/journal.pntd.0002885. eCollection 2014 May.


Blastocystis is an extracellular, enteric pathogen that induces intestinal disorders in a range of hosts including humans. Recent studies have identified potential parasite virulence factors in and host responses to this parasite; however, little is known about Blastocystis-host attachment, which is crucial for colonization and virulence of luminal stages. By utilizing 7 different strains of the parasite belonging to two clinically relevant subtypes ST-4 and ST-7, we investigated Blastocystis-enterocyte adhesion and its association with parasite-induced epithelial barrier disruption. We also suggest that drug resistance in ST-7 strains might result in fitness cost that manifested as impairment of parasite adhesion and, consequently, virulence. ST-7 parasites were generally highly adhesive to Caco-2 cells and preferred binding to intercellular junctions. These strains also induced disruption of ZO-1 and occludin tight junction proteins as well as increased dextran-FITC flux across epithelial monolayers. Interestingly, their adhesion was correlated with metronidazole (Mz) susceptibility. Mz resistant (Mzr) strains were found to be less pathogenic, owing to compromised adhesion. Moreover, tolerance of nitrosative stress was also reduced in the Mzr strains. In conclusion, the findings indicate that Blastocystis attaches to intestinal epithelium and leads to epithelial barrier dysfunction and that drug resistance might entail a fitness cost in parasite virulence by limiting entero-adhesiveness. This is the first study of the cellular basis for strain-to-strain variation in parasite pathogenicity. Intra- and inter-subtype variability in cytopathogenicity provides a possible explanation for the diverse clinical outcomes of Blastocystis infections.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antiprotozoal Agents / pharmacology
  • Blastocystis / drug effects*
  • Blastocystis / pathogenicity*
  • Blastocystis / physiology
  • Caco-2 Cells
  • Cell Adhesion / physiology*
  • Cell Membrane Permeability
  • Cell Proliferation / drug effects
  • Drug Resistance / physiology*
  • Host-Pathogen Interactions / physiology*
  • Humans
  • Metronidazole / pharmacology*
  • Tight Junctions / metabolism


  • Antiprotozoal Agents
  • Metronidazole

Grant support

The work was generously funded by grants from the National Medical Research Council (NMRC). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. HM and ZW acknowledge the generous research scholarship from the National University of Singapore.