Our main finding was the significant differences of fecal microbiota composition from patients with active UC vs those with remission UC and healthy subjects, with potential clinical application. Our study population was younger aged and most of them at advanced stages of UC. These characteristics are comparable with population from other studies exploring fecal microbiota [2, 28, 31, 32, 33, 71] whereas healthy subjects controls were volunteers from a family with a similar diet, expected to exert lower influence on the gut microbiota composition. Our results showed an increased proportion of the phylum Proteobacteria and the genus Fusobacterium, and Bilophila in active UC, which was significantly different from the group of remission UC and healthy subjects, who shared a microbiota profile of higher proportion of phylum Firmicutes, and genus Faecalibacterium, and Roseburia. These results are comparable with studies carried out by Franzosa et al., 2019, Kumari et al., 2013 and Sha et al., 2013. Particularly, the findings of reduced proportion of genus Lactobacillus, Faecalibacterium , and Roseburia in active UC, and their restoration in remission UC, has also been observed in previous reports [33, 34, 35, 36, 37, 73]. Such characterization is relevant due to scanty information regarding microbiota abundance in remission phase of UC, whereas consistent identification of specific genus in remission UC may be useful design for more efficient therapeutic strategies, prompted to reduce UC severity. Interestingly, particular bacterial composition like Faecalibacterium was shared by remission UC and healthy subjects. These bacteria have been reported to metabolize dietary components that promote colonic motility, maintain intestinal immune system and anti-inflammatory properties [38, 39, 40]. Consistently, reduced abundance of these microorganisms have been associated with a higher rate of recurrence of UC [41, 42, 43, 44, 45, 71] although increased levels of Faecalibacterium in stool samples have been associated with a lower activity index; supporting their role as potential biomarkers of disease severity and outcome, as suggested in other studies [46, 47].
Other findings were the higher abundance of the phylum Proteobacteria, and particularly the expansion of the genus Bilophila, in active UC. It is known that the relative abundance of Bilophila is promoted by diets enriched in saturated fats, which increase bacterial resistance to bile elimination. Furthermore, a change in the type of fat consumed impacts the composition of gut microbiota, which may modify the onset and severity of UC [39, 48,49]. Certain species of Fusobacterium show pro-inflammatory, invasive and adherent capacity to the intestinal mucosa, while increased proportion of Bilophila in the gut promotes an immune response mediated by Th1, resulting in the development of colitis in experimental mice model [50, 51, 52]. According to data from the present study, as well as those from the comparative studies [28, 29, 30], higher abundance of Fusobacterium and Bilophila was observed in the group with UC activity, while they tended to disappear in the remission phase.
Although direct pathophysiological mechanism is not possible to elucidate from the present study, we can propose that the relative abundance of some species are associated with the degree of inflammation and UC activity, derived from the inverse relation observed between the abundance of Fecalibacterium and Roseburia with calprotectin, a biomarker of severity of UC, which was consistent with a recent report [53]. Likewise, differences in bacterial richness, diversity, and dominance were highly related to the clinical scenarios studied. Remarkably, remission UC and healthy subjects showed the highest relative abundance of the phylum Firmicutes, which contributed to most of bacterial diversity and richness [54, 55, 56]. Further analysis of cluster distribution of bacterial communities showed differences in active UC, as compared to remission UC and healthy subjects, which was consistent with previous studies showing difference in the structure of microbiota between UC and healthy subjects [57, 58, 59].
Furthermore, studies characterizing gut microbiota composition and its modification during UC are relevant, since: a) UC provides a higher risk for colorectal cancer, whereas gut dysbiosis is thought to facilitate colorectal cancer development; b) the study of gut microbial communities during clinical phases of UC contributes to a better understanding of potential interactions with host immune response; c) characterization of specific genus of gut microbial communities may own potential clinical application derived from their association with active or remission phases of UC; and d) specific microbial manipulation, concomitant to antibiotic use, is currently used as a therapeutic approach for UC [49, 60, 61].
Finally, gut dysbiosis has been proposed as an important contributing factor to the increasing prevalence of UC, with a potential role for the related clinical-therapeutic phases [32, 62, 63]. Consistently, we found a significant ability of the genus Bilophila and Fusobacterium to selectively associate with cases of UC activity/remission. This agrees with the literature that describes a functional role for these bacteria in UC [64, 65, 66, 67] and suggests its potential clinical benefit for an early identification of clinical-therapeutic phases of UC [68, 69].
To our knowledge, this is the first study that investigated the composition of fecal microbiota in Mexican patients with active and remission UC. Our study faces some limitations. First, 16S rRNA analysis provides the taxonomic composition of the microbes present in the community and does not provide an analysis of the role of the microbiota in the disease. Second, data analysis may show limitations regarding the specific characterization of microbiota composition, as an isolated endpoint; however, we think that the analysis performed yields to an adequate interpretation within a translational context, highlighting the role of microbiota diversity in the clinical phases of UC. Third, a larger sample size may be required to confirm our data and further research is required to better characterize the role of gut microbiota in UC patients.
Here we provide a broad investigation of the fecal microbial community in Mexican patients presenting UC. We demonstrate differences in the microbiota communities in patients with active UC, remission UC, and healthy subjects. Selective association of gut dysbiosis with UC activity/remission may set the bases for further applications of non-invasive methods, clinically useful for an early identification of disease severity.