Dear Colleagues,

By definition, probiotics are bacteria displaying beneficial effects on human health, and their consumption has seen a huge increase in the pharmaceutical market in the last few decades. The reasons for such increasing interest are different. Probiotics may regulate important functions in the maintenance of the gut immune system through direct interaction with intestinal mucosa. Although their real effectiveness is strain-, dose-, and disease-dependent and the duration of therapy depends on the clinical indication, there is converging evidence that probiotics are effective for acute infectious diarrhea, antibiotic-associated diarrhea, Clostridium difficile-associated diarrhea, hepatic encephalopathy, ulcerative colitis, irritable bowel syndrome, functional gastrointestinal disorders, and necrotizing enterocolitis. Their capability to reduce intestinal hyperpermeability (leaky gut syndrome) has been postulated to be a key mechanism by which probiotics exert their beneficial activity. However, most of their properties, and especially how they interact with the host microbiota, are still not yet clarified. In addition to this, converging data show that via preservation of gut homeostasis, probiotics might, in some way, display beneficial effects in neuropsychiatric disorders induced by the so-called gut–brain axis connection. Moreover, in the last few years, a new class of recombinant probiotics has been attracting scientific interest, because they serve as bacteria capable of delivering therapeutic molecules to the gut. Such an approach could potentially be revolutionary in terms of novel therapeutic approaches for chronic diseases, and in some ways, it can go beyond the traditional “drug” concept. The present Special Issue is thus devoted to researchers from different areas, (i.e., basic and clinical gastroenterologists, microbiologists, pharmacologists, neuropsychopharmacologists) involved in this vast research field in the attempt to discuss new achievements in the field of probiotic impacts on human disease, starting with gut homeostasis control. In this sense, we also invite submissions on the intimate connection between probiotics and metabolic disorders featuring leaky gut conditions, such as diabetes and obesity, and the neuropsychiatric disorders associated with them.

Dr. Giuseppe Esposito
Dr. Giovanni Sarnelli
Dr. Luisa Seguella
Dr. Marcella Pesce
Guest Editors

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• Leaky gut
• Colitis
• Metabolic disorders
• Obesity
• Microbiota
• Gut–brain axis