Low eukaryotic viral richness is associated with faecal microbiota transplantation success in patients with UC.

We read with interest the recent Gut study by Zuo and colleagues showing that a good outcome of faecal microbiota transplantation (FMT) in Clostridium difficile infection (CDI) was associated with bacteriophage transfer.1 FMT is an established treatment to restore a balance in disturbed intestinal microbiotas of patients with CDI,2 3 and recent multicentre randomised, double-blind, placebo-controlled trials showed its effectiveness in inducing clinical and endoscopic remission in patients with UC.4 We examined the gut virome dynamics of nine patients with UC who were undergoing FMT (64 patient and 8 healthy donor samples).5 Two patients with UC achieved long-lasting complete remission with mucosal healing (u003e2 years; figure 1: patient 1 and 3), and one patient reported temporary remission for 6 weeks (figure 1; patient 4).5 The remaining six patients did not respond to treatment. Using the NetoVIR protocol,6 we analysed the faecal virome (both RNA/DNA genomes of phages and eukaryotic viruses) using tailored bioinformatics approaches (see online supplementary data). Irrespective of their outcome, no statistical differences were observed in phageome richness between patients with UC and healthy donors (figure 2A) at any time point, in contrast …