T. spiralis and Campylobacter jejuni reduce SERT expression in the gut [100,101], while L. rhamnosus upregulated gene expression and protein levels of SERT in a rat model of PI-IBS [100], and Lactobacillus acidophilus and Bifidobacterium longum supernatants to upregulate SERT expression in HT-29 and Caco-2 cells [102]. This evidence concerns the gene SLC6A4 and irritable bowel syndrome.