| Summary: | In our previous study the enrichment of the intestinal proteome of type 1 diabetes (T1D) children with <i>Bacteroides</i> proteins was observed, which led us to our current study that aimed to isolate and characterize <i>Bacteroides</i> species from fecal samples of T1D and control children. Repetitive sequence-based PCR (rep-PCR) was used for typing the isolated <i>Bacteroides</i> species. The antibiotic susceptibility and mucinolytic activity of the isolates was determined. The quantification of specific bacterial groups in the fecal samples was determined by qPCR. The ability to adhere and invade the human colonic cell line HT29-MTX-E12 of strains of <i>P. dorei</i>, <i>B. uniformis</i> and <i>P. distasonis</i> was determined and their whole genome sequencing was performed. The results showed similar numbers of <i>Bacteroides</i> species in T1D and control samples, but unique <i>Bacteroides</i> species and a higher recovery of <i>P. distasonis</i> from T1D samples was observed. Rep-PCR grouped the different <i>Bacteroides</i> species, but no discrimination by origin was achieved. T1D children showed a significant increase in <i>Proteobacteria</i> and a depletion in <i>Lactobacillus</i> sp. All tested <i>P. dorei</i>, <i>B. uniformis</i> and <i>P. distasonis</i> were able to adhere to HT29-MTX-E12 cells but significant differences (<i>p</i> < 0.05) in the ability to invade was observed. The highest ability to invade was exhibited by <i>P. distasonis</i> PtF D14MH1 and <i>P. dorei</i> PtFD16P1, while <i>B. uniformis</i> strains were unable to invade. The damage to tight junctions was also observed. The presence of <i>Lactobacillus</i> sp. inhibited the invasion ability of <i>P. distasonis</i> PtF D14MH1 but not <i>P. dorei</i> PtFD16P1. Sequences of agonist peptides of the human natural preproinsulin and the insulin B chain insB:9-23 peptide mimics were identified. The results reported in our study stresses the continued efforts required to clarify the link between T1D and gut microbiota.
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