The aim of this pilot study was (1) to assess the use of B. longum ES1 treatment in a homogeneous group of patients with IBS-D, by evaluating clinical response, through the use of validated questionnaires for IBS, and serological response, by the determination of serum levels of inflammatory cytokines and zonulin, in order to analyse potential effects on immune modulation and restoration of the intestinal barrier, respectively, and (2) to evaluate differences in response depending on the treatment duration. The gene discussed is HP; the disease is irritable bowel syndrome.