What About the Gut Flora in IBS: Do Antibiotics/Probiotics Work?

John K. DiBasie, MD, FACG

The last decade has seen a renewed interest in the bacteria residing within our gastrointestinal tract—the gut microbiota—particularly as it relates to the pathogenesis of disease and how its modifications may be an effective means to treat disease. As a result, there has been an explosion of interest in the therapeutic modulation of the enteric micriobiota using “biotics”—antibiotics, prebiotics, probiotics, and synbiotics. This presentation focused on the evidence surrounding the use of antibiotics and probiotics in the management of the IBS.

What’s the Rationale for Modifying the Gut Microbiota to Treat IBS?The etiology of IBS is unknown but is suspected to be multifactorial. It has been suggested that alterations in the gut microbiota are present in IBS that both affect gut permeability and lead to immune and mast cell activation ultimately affecting gut sensorimotor function, thereby resulting in the symptoms’ characteristics of IBS. These alterations in gut microbiota may occur following and enteric infection (ie, post-infectious IBS), small bowel overgrowth, and the ambiguous gastrointestinal “dysbiosis.”

Do Antibiotics Help to Relieve Symptoms in IBS?Despite earlier suggestions that exposure to antibiotics may increase the risk of developing IBS, more recent work provides evidence of a beneficial effect of antibiotics on reducing IBS symptoms. Indeed, several small studies have shown that treatment with systemic antibiotics reduces IBS symptoms, although the magnitude and duration of the benefit has been highly variable. Although some reports suggest that symptom benefit correlates with improvements in lactulose breath hydrogen measurements, other reports suggest the contrary. Due to concerns of serious side effects and antibiotic resistance of systemic antibiotics, recent research has focused on the use of non- (or poorly) absorbed oral antibiotics (eg, neomycin, rifaximin). The preliminary results of tow large phase 3, placebo-controlled clinical trials of rifaximin in non-constipated IBS were recently reported, and both demonstrated significant improvement in overall IBS symptoms and bloating.

What Are Probiotics and How Do they Work?A probiotic is generally defined as a living microorganism that, when ingested in sufficient amount, confers some benefit to the health of the host. Characteristics of an effective probiotic organism include the ability to resist degradation in its passage through the gut, to adhere to the epithelium and colonize the lumen, to stabilize the commensal flora and prevent adherence by pathogens, to exert a beneficial effect on the host, and to be safe for human use. The most common genera from which probiotic organisms are derived include Lactobacillus, Bifidobacterium, Enterococcus, andStreptococcus. The yeast, Saccharomyces boulardii, is also considered a probiotic organism.

Although, likely multifactorial, the most important mechanisms appear to relate to modifications in immune and inflammatory responses. Inhibition of bacterial translocation by stabilization of mucosal barrier function, release of antimicrobial substances, stimulation of regulatory T-cells with modification of cytokine release, and down regulation of virulence factors seem to be particularly important effects. Competition and exclusion of pathogenic bacteria, enhancement of intestinal motility and blood flow, and the lowering of luminal pH may also play a role with some probiotic microbes. Nevertheless, most of these effects are based mostly on in vitro and animal studies; therefore, their importance/relevance to humans remains to be determined. In addition, it is important to recognize that all probiotic organisms do not work the same way and, therefore, should not be expected to exert the same beneficial effects.

Do Probiotics Help to Relieve Symptoms in IBS?A number of studies have been conducted using a variety of probiotic agents in IBS patients. Although most studies are of poor quality and have yielded conflicting results, the most consistent benefits have been seen in reduction of gas and bloating. A recent, well-done, albeit short duration, study in women with non-constipated IBS, demonstrated a significant benefit on global IBS symptoms with use of the probiotic Bifidobacterium infantis.

ConclusionMicroorganisms within the gut play an important role in human development and the maintenance of human health. Accumulating evidence suggests that alterations in our gut microbiota may result in a variety of disorders. The clinical role of manipulating the guy microbiota to treat IBS appears promising; however, more evidence-based research is needed to firmly establish the benefits of this approach.

Adapted from material provided in the American College of Gastroenterology 2010 Annual Scientific Meeting Breakfast Sessions guide, provided to attendees of the conference.