**4. Conclusions**

Currently, the role of bacterial gu<sup>t</sup> microbiota is described as a key factor in the development of Crohn's disease, we do know that, for the disease to develop, dysbiosis or a definitive change in the intestinal microbiota must occur. This study may provide additional evidence regarding potential non-invasive tools such as microbiota-based biomarkers of the response before and after anti-TNF therapy in Crohn's disease as a starting point for future clinical trials. These trials could determine the most effective treatment among not only these therapies but all therapies used in the managemen<sup>t</sup> of Crohn's disease based on patient microbiota and provide more appropriate, inexpensive and non-invasive tools for predicting clinical response to treatment, reduce morbidity rates and improve efficiency.

**Author Contributions:** L.S.-A. participated in the design of the study and drafted the manuscript, revising for important intellectual content, and fully approved the final version for submission. J.F.M.-B. participated in the design of the study, contributed to the statistical analysis plan and was also involved in the drafting of the manuscript. S.M.-V. participated in design of the study related to gu<sup>t</sup> microbiota analysis and contributed to the statistical analysis plan. E.C.-C. participated in the design of the study, contributed to the statistical analysis plan and was also involved in the drafting of the manuscript, revising for important intellectual content, and fully approved the final version for submission. J.R.-M. participated in the design of the study and its coordination. X.C.-R. conceived of the study and was involved in the overall design and helped to draft the manuscript revising for important intellectual content, and fully approved the final version for submission. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Acknowledgments:** The authors thank Maria Repice and Ian Johnstone for their help with the English version of the text.

**Conflicts of Interest:** The authors declare that there are no conflicts of interest to disclose.
