title: Phenotypic variation in Blastocystis sp. ST3.
abstract: BACKGROUND
  Blastocystis, is one of the most common human intestinal protozoan, which has many conflicting reports on its pathogenic role. Gut conditions which obviously varies in asymptomatic individuals, symptomatic and irritable bowel syndrome (IBS) patients in terms of gut flora, pH, osmotic pressure and water potentials could play an important role in its pathogenicity. The present study is the first study to investigate phenotypic characteristics of Blastocystis sp. ST3 isolated from asymptomatic, symptomatic and IBS isolates.
  
  
  METHODS
  A total of 8 Blastocystis isolates were obtained from four IBS patients (IBS1-4) and four symptomatic patients (S1-4) at a local gastroenterology clinic. Asymptomatic isolates (A1-4) were obtained from a field survey at a local village.
  
  
  RESULTS
  All 12 isolates were determined as subtype 3 (ST3). A1-4 isolates showed the highest peak growth followed by IBS1-4 isolates and S1-4 isolates for the growth profile. Parasites from IBS isolates (IBS1-4) showed the largest diameter with a mean 18.43 ± 2.22 μm compared to parasites of symptomatic isolates (isolates S1-4) 15.54 ± 3.02 μm and asymptomatic isolates (isolates A1-4) 11.76 ± 0.82 μm. The symptomatic isolates (average generation time: 9.87 ± 2.97 h) grew faster than the IBS isolates (average generation time: 7.56 ± 1.06 h) and asymptomatic isolates (average generation time: 5.97 ± 1.52 h). The parasites isolated from IBS isolates showed strong aggregation and clumping, which had seen reduced in parasites of isolates S1-4. No clumping was seen in parasites from A1-4. The outer surface of parasites in IBS isolates showed greater binding affinities towards FITC-labelled Concanavalin A (Con A) than symptomatic isolates and asymptomatic isolates. Scanning electron microscopy showed that in IBS isolates, the surface of Blastocystis showed a very coarse and intensely folded surface. The IBS isolates also exhibited a dense material and a thicker layer of surface coat can be seen compared to asymptomatic and symptomatic isolates.
  
  
  CONCLUSIONS
  There have been no studies thus far providing evidence for phenotypic variation within a particular subtype. The present study is the first to demonstrate the phenomenon of gut environment facilitating adaptation of parasites possibly for survival leading to phenotypic differences for Blastocystis.
authors.forename: Nanthiney Devi
authors.initials: ND
authors.lastname: Ragavan
authors.affiliation: Department of Parasitology, Faculty of Medicine, University of Malaya, Kuala Lumpur 50603, Malaysia. suresh@um.edu.my.
authors.forename: Suresh Kumar
authors.initials: SK
authors.lastname: Govind
authors.forename: Tan Tian
authors.initials: TT
authors.lastname: Chye
authors.forename: Sanjiv
authors.initials: S
authors.lastname: Mahadeva
mesh_terms: D016844:Blastocystis / Q000502:physiology* / Q000648:ultrastructure*; D016776:Blastocystis Infections / Q000469:parasitology*; D006801:Humans; D043183:Irritable Bowel Syndrome / Q000469:parasitology; D010641:Phenotype