P1215 Blastocystis is very rare in faeces of children with Crohn’s disease: quantity, subtyping and association with the faecal bacteriome

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Abstract Background Blastocystis is a single-cell gut protist, presumably an indicator of gut health. We aimed to assess its occurrence and subtypes in a longitudinal set of faecal samples from recently diagnosed paediatric patients with Crohn's disease (CD) and compare it to similar longitudinal collections from children having other chronic immunopathological diseases without gut pathology (type 1 diabetes, T1D, and juvenile idiopathic arthritis, JIA), as well as to control subjects. Methods At a single tertiary centre, 626 samples were collected from 156 subjects: 40 with CD (mean age 12.5 years), 57 with T1D, 10 with JIA and 49 healthy. Specific real-time PCR detected and quantified Blastocytis, whereas massively parallel amplicon sequencing showed its subtype. The relationship between Blastocystis and the bacterial community was assessed by 16S rDNA amplicon profiling. Results Blastocystis was detected in 4.0% (9/223) stool samples in CD, six of them being of a very high quantity and originating from a single patient in long-term remission with a less common CD phenotype (L2, colonic, according to Paris classification). Subject-wise positivity of Blastocystis in CD (3/40, 7.5%) was significantly lower than in either T1D (21/57, 37%), JIA (2/10, 20%), or in healthy children (14/49, 29%). There was no notable difference in the subtype repertoires among diagnoses. The faecal bacteriome had higher alpha diversity in Blastocystis-positive samples. The Blastocystis-positive bacteriomes had slightly yet significantly (p<0.001) different overall community composition across all diagnoses (Figure 1), which was also reflected by the suggestive differential abundance of several taxa (e.g. Ruminococcaceae and Prevotellaceae increased, Bacteroidaceae and Rikenellaceae decreased). Conclusion We performed a large molecular survey on Blastocystis in longitudinal samples of three different paediatric diagnoses and healthy subjects. We document an unusual long-term carriage of very high loads of Blastocystis in a patient with colonic CD phenotype in clinical remission. Otherwise, however, Blastocystis is very rare among paediatric patients with CD, in contrast to two other chronic immunopathologic childhood diagnoses (T1D, JIA). Further longitudinal observation will show whether Blastocystis might return in patients with well-controlled CD upon ameliorating their bacteriome composition. Institutional Grants/Research Supports Supported by Ministry of Education, Youth and Sports of the Czech Republic, programme INTER-EXCELLENCE II, project LUC23165.

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