Background: Blastocystis spp. is a common protozoan parasite that shows extensive genetic diversity
with 16 different subtypes (STs) identified in humans.
Objective: To determine the detection rates and subtypes of Blastocystis spp. in colorectal cancer (CRC)
patients, irritable bowel syndrome (IBS) patients, and asymptomatic individuals (participants with no
GIT symptoms) in Sohag, Egypt.
Subjects and Methods: The study was conducted on 225 stool samples collected from 75 CRC patients,
75 IBS patients, and 75 asymptomatic participants with no GIT symptoms. All samples were examined
microscopically by direct smears and formalin ethyl acetate concentration technique (FECT), and cultured
on modified Jones' medium supplemented with 10% donkey serum. The genomic DNA was extracted from
positive stool samples. Conventional and nested PCRs (nPCR) were used to amplify the small-subunit
ribosomal RNA (SSU rRNA) encoding gene of Blastocystis spp.; and subtypes were identified by restriction
fragment length polymorphism (RFLP) of nested PCR products using Hinf I and Rsa I.
Results: Out of 225 stool samples, Blastocystis was detected in 97 samples (43.1%) by culture, 89 samples
(39.6%) by direct smears, and 71 samples (31.6%) by FECT with significant difference (P=0.035). The
sensitivity of direct smears and FECT compared to culture was 87.6% and 73.2% while the specificity was
96.9% and 100%, respectively. The presence of Blastocystis spp. was significantly higher in CRC (53.3%)
and IBS groups (48%) than in the asymptomatic group (28%) (P=0.004). Out of 97 positive fecal samples,
Blastocystis SSU rRNA gene was amplified in 45 (46.4%) samples by conventional PCR and 95 (97.9%)
samples by nPCR. RFLP analysis identified three STs, where ST3 was more common in CRC than IBS and
asymptomatic groups (85%, 74.3%, 75%, respectively) followed by ST1 (15%, 20%, 25%, respectively).
While ST2 was recorded in only 5.7% of the IBS group. However, there was no significant difference
between Blastocystis STs and socio-demographic, and clinical groups.
Conclusion: Detection rate of Blastocystis spp. was higher in CRC patients and IBS patients than in
asymptomatic group and ST3 was the most prevalent subtype in studied groups.