Abstract
The importance of the human microbiota in human health and disease has been suggested by a vast body of research in recent decades. In the specific, the human microbiota plays a crucial part in the development of many diseases, including infections, liver problems, metabolic disorders, respiratory illnesses, mental or psychiatric illnesses, and autoimmune diseases. The administration of potentially helpful bacteria, known as probiotics, can be used for manipulating the microbiota for therapeutic purposes. Today, probiotics are defined as “live microorganisms which when administered in adequate amounts confer a health benefit on the host’ according to guidelines set by the World Health Organization and the Food and Agriculture Organization of the United Nations”. Numerous studies, reviews, and systematic reviews have reported on the impact of probiotics on host health. Probiotic bacteria are sold and consumed as naturally fermented or non-fermented food products in a variety of matrices, food supplement powders, pills, etc. Data from in vitro tests and animal models show that among studied putative probiotic strains, performance varies by strain. For these reasons, probiotics products for different applications were investigated in this research thesis. In the specific, the first study aimed at investigating the potential of a novel functional herbal tea to act as the carrier for the probiotic Bacillus coagulans GanedenBC30. We were able to confirm the survival of the spores during the infusion treatments, with only a slight effect on the spore survival from the simulation of the gastrointestinal transit. An in-depth investigation using the Simulator of the Human Intestinal Microbial Ecosystem (SHIME) which incorporated mucin-covered microcosms allowed us to demonstrate that the probiotic quickly colonized mucosal compartments and persisted after 4 days of wash-out. By summing the luminal and mucosal values and referring to the whole volume of the colon bioreactors, the content of viable cells of B. coagulans GanedenBC30 was largely above the probiotic threshold. Investigating the vaginal environment and its probiotic needs, we performed analyses to create a multi-strain probiotic gel that would foster a lactobacilli-dominated vaginal microbiota in pregnant women and ensure appropriate eubiosis for the newborn. Nomadic lactobacilli (95 strains), mostly isolated from food sources, were preliminarily screened for functional traits before being characterized for their capability to inhibit the two vaginal pathogens (Streptococcus agalactiae and Candida albicans) which may lead to adverse pregnancyrelated outcomes. Later, on the eight best-performing strains, the ability to form biofilm was tested and two strains were finally selected to understand their ability to reduce the inflammation caused by C. albicans infection on the reconstituted human vaginal epithelium (HVE). Based on a multi-step and cumulative scoring-based approach, the probiotic potential of two nomadic lactobacilli strains (L. plantarum C5 and POM1), was confirmed to be applicable to preserve and improve human vaginal health. The ability of lactic acid bacteria to improve gastrointestinal digestion through probiotic formulation was investigated first by evaluating the survival under gastrointestinal tract conditions, and then performing target assays (e.g., evaluation of the hydrolysis of anti-nutritional compounds, the peptidase activity, the total peptides content, and the bioavailability of phenolic compounds in partially digested matrices). A scoring procedure was assessed to finally select the most promising combinations of strains, to cover all the functional characteristics, which were then recommended to be used as dietary supplements or pharmacological preparation. Moreover, selected probiotic preparation of Lactobacillus and Bacillus spp. was used to understand its ability to degrade gluten throughout a double-blind, placebo-controlled, and randomized in vivo challenge from participants following a gluten-controlled diet. Fecal and urine samples were collected on specific days (time points) pre-defined in a calendar and corresponding to different amounts of gluten intake. The finding from this analysis suggests that this probiotic combination has the potential to break down gluten residues, making it a useful supplement to the glutenfree diet for enhancing celiac patients' quality of life. In general, better gluten breakdown may improve the health of the population by improving digestive processes. In conclusion, we were able to investigate the activity of potential probiotic bacteria that may be selected either for the gut or vaginal environment to establish a balanced microbiota in the host.