Probiotics: Properties, Examples, and Specific Applications
Abstract
Probiotics are beneficial components of the microbiota that have been used for centuries because of the health benefits they confer to the host. Only recently, however, has the contribution of probiotics to modulation of immunological, respiratory, and gastrointestinal functions started to be fully appreciated and scientifically evaluated. Probiotics such as Escherichia coli Nissle 1917 and lactic acid bacteria are currently used to, or have been evaluated for use to, prevent or treat a range of intestinal maladies including inflammatory bowel disease, constipation, and colon cancer. Engineering these natural probiotics to produce immunomodulatory molecules may help to further increase the benefit to the host. In this article, we will discuss some of the mechanisms of action of probiotics as well as advances in the rational design of probiotics.
Probiotics are defined as living bacteria that, when administered in adequate amounts, confer a health benefit on the host (FAO/WHO 2001). The original observation of the beneficial properties conferred by some bacteria is attributed to the Nobel Prize winner Eli Metchnikoff, who is regarded as the grandfather of modern probiotics. In the early 20th century, Metchnikoff discovered that “healthy bacteria,” especially lactic acid bacteria (LAB), can have a positive influence on digestion and the immune system (Anukam and Reid 2008). Most microorganisms recognized to date as probiotics are Gram-positive, with Lactobacillus and Bifidobacterium being the main species used as treatments of intestinal dysfunctions (Marco et al. 2006). However, some Gram-negatives are also used as probiotics. The best example of this group is Escherichia coli Nissle 1917 (EcN) (Nissle 1959), also known as “Mutaflor,” which has been used in Germany for many years in the treatment of chronic constipation (Mollenbrink and Bruckschen 1994) and colitis (Schutz 1989).
In the last century, many studies have reported probiotic bacteria to play important roles in the modulation of immunological, respiratory, and gastrointestinal functions (Floch et al. 2011). Furthermore, probiotics have been shown to play a protective role by directly competing with intestinal pathogens through the release of antibacterial substances such as bacteriocins (Cotter et al. 2005) or metabolites such as acetic acid and lactic acid (Servin 2004). Although most studies on probiotics have been empirical, new advancements may originate from research on the interactions between commensal microorganisms (termed the microbiota), pathogens, and the host. Understanding the mechanisms of gut colonization in both normal and inflammatory conditions is essential to designing probiotics for a specific use. In this article, we will discuss some of the recent developments on the mechanisms of action of probiotics and their utilization for delivering molecules to specific sites within the host.
ACKNOWLEDGMENTS
We acknowledge Sean-Paul Nuccio for help with editing this article. Work in M.R.’s lab is supported by National Institutes of Health Public Health Service grant AI083619 and by the Pacific Southwest Regional Center of Excellence. J.B. is supported by a postdoctoral fellowship of the American Heart Association (11POST7090006).
Footnotes
Editors: Pascale Cossart and Stanley Maloy
Additional Perspectives on Bacterial Pathogenesis available at www.perspectivesinmedicine.org