Probiotics and Microflora

Max Sherman, RPh

Disclosures

US Pharmacist. 2009;34(12):42-44. 

In This Article

New Research

Microbiologists from Louis Pasteur (1822–1895) and Ilya Mechnikov (1845–1916) to present-day scientists have emphasized the importance of understanding the contributions of our microbiota to human health and disease. Mechnikov, who won the Nobel Prize for Physiology and Medicine in 1908, was one of the first researchers to study the flora of the human intestine.[16] He developed a theory that senility is due to poisoning of the body by the products of these bacteria. To prevent them from multiplying, he suggested a diet containing milk fermented by bacilli, which produce large quantities of lactic acid.[16]

Today, science is on the verge of understanding how the body maintains a state of equilibrium with its incredibly complex enteric microflora.[17] Appropriate immune recognition is also essential to host-bacteria symbiosis (i.e., the biological association of two individuals or populations of different species). It has recently been shown that the recognition of commensal bacteria by epithelial cells protects against intestinal injury.[17] Other research indicates that use of antibiotics reduces the capacity of intestinal microflora to metabolize phytochemicals into compounds that may protect against cancer.[18] However, antibiotic use also disrupts the intestinal microflora metabolism of estrogens, which results in lower levels that might decrease the risk of some hormonal cancers. Use of antibiotics may be associated with cancer risk through effects on immune function and inflammation, although little is known about these mechanisms.[19,20]

Intestinal bacteria release chemical signals recognized by specific receptors—called toll-like receptors (TLRs)—of the innate immune system. The interaction helps to maintain the architectural integrity of the intestinal surface and enhance the ability of the epithelial surface to withstand injury. A deficiency in any of the numerous signaling molecules can induce intestinal inflammation, which may be a precursor of inflammatory bowel disease. Research is now ongoing to understand various types of TLR activation to ascertain how this information can be used to treat irritable bowel syndrome, Crohn's disease, and other types of intestinal inflammatory conditions.[21]

A group of medical researchers in Ireland recently identified five probiotic bacteria than can prevent Salmonella infection in pigs and, if translatable to humans, could potentially reduce Salmonella-induced foodborne illnesses, which cause between 500 and 1,000 deaths every year in the U.S.[4] This same group is also investigating the human microbiome for antimicrobials against pathogens. They have isolated a compound called lacticin 3147 from the harmless bacterium Lactococcus lactis, which is used to make cheese. Recently, lacticin 3147 has demonstrated antimicrobial activity against a range of genetically distinct Clostridium difficile strains isolated from the human gut. This indicates that lacticin 3147 may offer a new treatment for C difficile–associated diarrhea, a serious condition that affects 3 million people per year in the U.S. and is a major problem in hospitals.[4]

There is evidence confirming the effects of Lactobacillus GG in preventing diarrhea and atopy in children.[22,23] These organisms are thought to occupy binding sites in the gut mucosa that prevent pathogenic bacteria from adhering. Lactobacilli also produce bacteriocins that act as local antibiotics. Diarrhea associated with antibiotics may result when the antibiotics disrupt the normal flora in the gut of a healthy person. Such disruptions cause dysfunction of the gut's ecosystem and allow pathogens to colonize the gut and gain access to the mucosa. A number of organisms have been studied as probiotics to prevent antibiotic- and C difficile–associated diarrhea (Table 1).[24] Whether probiotic supplements stop this process by reducing the disruption or by acting as substitutes for healthy flora is unclear.

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