Abstract
Microorganisms efficiently colonize the external and internal surfaces of the animal body establishing mutually beneficial interactions and forming site- and individual-specific microbiota. The degradation of complex polysaccharides in the animal gut, the production of useful compounds, protection against pathogenic microorganisms and contribution to the development of an efficient immune system are the main beneficial effects of a balanced microbiota. A dysbiosis, an imbalanced composition of the microbiota, has been associated with a large number of diseases from gastro-intestinal or urogenital disorders to allergies, cardiovascular and autoimmune diseases and even to the onset of certain cancers. A growing body of evidence has indicated that probiotic treatments, aimed at maintaining or rebalancing the microbiota, are useful to treat/prevent those illnesses. Lactic Acid Bacteria and Bifidobacteria are the most common microbes used in probiotic preparations; however, other bacteria and yeast cells are also widely used in commercial products. Here we focus on the use of bacterial spore formers as probiotics. Spore formers have been marketed as probiotics for over 50 years and are now extensively used for the treatment of intestinal disorders and as dietary supplements in humans, as growth promoters and competitive exclusion agents in animals.
Highlights
Microorganisms efficiently colonize the external and internal surfaces of the animal body establishing mutually beneficial interactions and forming site- and individual-specific microbiota
When growth is no longer possible, cells enter the sporulation cycle, a microbial example of differentiation: (i) Asymmetric cell division occurs creating two cells of different sizes, a small prespore and a large mother cell; (ii) the mother cell engulfs the prespore, which becomes a protoplast in the mother cell cytoplasm; (iii) both cells contribute to the maturation of the prespore into the mature spore by progressive dehydration of the prespore cytoplasm and by forming a series of protective layers; (iv) the mature spore is released in the environment by the lysis of the mother cell
Examples of Bacillus probiotics tested in farmed animals include studies performed on chickens infected with Escherichia coli O78:K80, Salmonella enterica or Clostridium perfringens that were protected when pre-dosed with B. subtilis spores [47,48]
Summary
A series of in vitro and in vivo reports indicate that the interaction with spores of various Bacillus species modulates the immune response. In an in vivo study with a murine model, orally administered spores of B. subtilis of a laboratory wild-type strain and an isogenic mutant unable to germinate were both able to induce similar levels of spore-specific fecal sIgA and serum. A more recent study showed that B. subtilis spores protected in vitro human keratinocytes from oxidative stress and other chemically induced injuries [34]. Antioxidant activity has been associated with B. megaterium spores, both in vitro on Caco-2 cells and in vivo on a murine model of dextran sodium sulfate (DSS)-induced oxidative stress [35]
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