With the outstanding advancements in genetic engineering, we recently witnessed the development of bacterial/probiotic strains genetically engineered to either act as “intestinal biosensors” (detecting inflammatory markers) or as “resident cells’ factories” of therapeutic molecules (biotherapeutics improving drug delivery at the mucosal surface) [,]. Most engineering approaches have focused on the transfection of plasmids encoding for immunoregulatory cytokines, reporter substrate, or anti-inflammatory mediators (). Plasmids are small circular DNA molecules physically separate from chromosomal DNA and replicate independently. Their easy transfection into bacterial cells made them the major vector for inducing recombinant DNA expression into desired probiotic strains. Basic plasmid consists of essential DNA sequences that include a DNA replication origin, an antibiotic resistance gene (to select the transfected bacteria from non-transfected one), and the region referred to as the “Multiple Cloning Site”, in which exogenous DNA fragments are inserted by restriction enzymes. By recombinant DNA methods, the desired genes are spliced into a plasmid, which may also contain promoter regions to make plasmid expression chemically controlled (i.e., substrate and/or specific biomarkers). Both biosensors and biotherapeutic probiotics answer major unmet needs in IBD care. IBDs are chronic relapsing diseases in which a deep control of the mucosal inflammatory process (the so-called “mucosal healing”) represents the current goal of treatment. This, on one hand, implies that patients should undergo chronic immunosuppressive treatment, with undesirable systemic side effects, whilst, on the other, repeated invasive and costly investigations (i.e., endoscopies and biopsies) are often necessary to evaluate the presence of relapse and/or to detect residual signs of mucosal inflammation after treatment. Biosensors are live bacteria engineered to respond to specific biomarkers, indicative of inflammation, by producing a reporter substrate that could be easily detected (such as fluorescent proteins), hence limiting the need for invasive testing. To this aim, several biosensors have been recently developed to respond to markers of intestinal inflammation [,] or bleeding []. Yet, biosensors should display high sensitivity and specificity toward the selected biomarker to be used as diagnostic tools. This approach is, therefore, currently hampered by the limited knowledge of relevant biomarkers specific to gut inflammation and the number of characterized bacterial systems that can be reliably used as disease-responsive circuits. Given these shortcomings, most published studies have focused on developing engineered probiotics capable of expressing therapeutic molecules (biotherapeutic probiotics), either constitutively or “on-demand” through inducible systems that respond to exogenously administered substrates (commonly added to food or water) or to locally produced biomarkers (“sense and respond systems”) (). All biotherapeutic probiotics are live bacteria designed to produce in situ anti-inflammatory molecules, offering the main advantage of achieving the topical release of therapeutics. Anti-inflammatory or immunosuppressant agents, indeed, may be released directly in situ, maximizing therapeutic concentrations in the target tissue using relatively smaller doses of the therapeutic compound, thus limiting systemic side effects. Constitutive systems offer the unquestionable advantage of using relatively simpler genetic modifications, mostly expressed in a constitutive fashion by the chosen probiotic platform. However, this comes to a cost considering the large amount of energy required for the probiotic to constitutively express these substances, while also exposing the risk of overproducing the therapeutic substance in unwanted sites, potentially hindering their effectiveness and safety, respectively., Engineered probiotics represent a cutting-edge therapy in intestinal inflammatory disease (IBD). Genetically modified bacteria have provided a new strategy to release therapeutically operative molecules in the intestine and have grown into promising , Learn which probiotics help for IBD and which to avoid. Crohn's, Ulcerative Colitis, Microscopic Colitis, Pouchitis and more..