The pathogenic role of different Blastocystis hominis genotypes isolated from patients with irritable bowel syndrome.

Background And Study Aims: The pathogenic role of Blastocystis hominis is still regarded by some as controversial. Studies have been in progress for years to evaluate the role of blastocystosis in irritable bowel syndrome (IBS) and demonstrated that faecal carriage of B. hominis was frequent in these patients. This study attempted to distinguish different genotypes of B. hominis isolates obtained from patients with IBS and to evaluate their pathogenic potentials.

Patients And Methods: One hundred subjects (51 patients with IBS and 49 asymptomatic infected subjects) harbouring B. hominis were investigated by a direct smear examination and in vitro culture of stool samples followed by genotyping of B. hominis by PCR using STS primers. Sigmoidoscopy was done in all subjects and biopsies were taken and subjected to histopathologic examination.

Results: Genotyping proved that only four genotypes of B. hominis were identified. In patients with IBS, genotypes III, I, and IV were detected (28, 15 and 14 isolates, respectively). On the other hand, genotypes III, IV, and II were identified in asymptomatic infected individuals (21, 19 and 13 isolates, respectively). The degrees of chronic inflammatory changes in sigmoidoscopic biopsies caused by B. hominis genotypes among IBS patients revealed that severe inflammation was present mainly in patients harboring genotype I isolates (4/15) (26.66%), while genotype III caused severe inflammation only in 9.09%. Genotype II isolates were not detected in IBS cases. Asymptomatic infected individuals harboring genotypes II, III and IV exhibited mild to moderate inflammatory changes. Genotype I isolates were not detected in asymptomatic infected group. The correlation between different B. hominis genotypes and degree of inflammation was statistically insignificant.

Conclusion: Genotype I was the most pathogenic genotype of B. hominis isolates in patients with IBS while genotype II was not detected among those patients. Also, our results suggest the presence of pathogenic and non-pathogenic strains among genotypes III and IV.