Fecal microbiota transplantation (FMT), an emerging therapy for conditions like irritable bowel syndrome (IBS), continues to raise questions about the safety of transferring certain microorganisms, especially the intestinal parasite Blastocystis spp. In a new long-term study, researchers investigated the potential for Blastocystis spp. transmission via fresh, unfrozen FMT, shedding light on a contentious topic within microbiome-based therapies.
The trial enrolled adolescents aged 16-20 with refractory IBS who received two administrations of fresh allogeneic FMT, at baseline and 6 weeks later, via a nasoduodenal tube. The donor feces, notably colonized with Blastocystis subtype 3 (ST3), were confirmed viable through microscopy, culture, PCR, and sequencing. Importantly, viable Blastocystis spp. were only detected in fresh, but not frozen, donor samples.
Three recipients participated in the study. At the outset, two were negative for Blastocystis spp., while one carried a different subtype (ST2). Following FMT, the two initially negative participants acquired the donor’s ST3 subtype by Week 12. However, this colonization proved temporary, with both losing the ST3 subtype by Weeks 24 and 48. The third recipient, originally colonized with ST2, maintained their existing colonization without acquiring ST3.
Transient adverse events were reported, consistent with those seen in recipients of Blastocystis-negative FMT, and no serious FMT-related adverse events occurred. This suggests that while fresh FMT can transmit viable Blastocystis spp., the colonization may be short-lived and clinically insignificant.
This study provides the first long-term data on Blastocystis spp. transmission through fresh FMT and contributes valuable evidence to the ongoing debate about donor screening guidelines. Current European consensus no longer advises rejecting donors testing positive for Blastocystis, and these findings may further inform donor selection protocols in clinical practice.
Reference:
Olminkhof L et al. Transient colonization with Blastocystis spp. after transmission via fecal microbiota transplantation. Gut Microbes. 2024;16:2282846.
