The causes of intestinal dysbiosis: a review

Alternative Medicine Review, June, 2004 by Jason A. Hawrelak, Stephen P. Myers

Recent epidemiological research has shown that individuals who had taken only one course of antibiotics had significantly lower serum concentrations of enterolactone up to 16 months post-antibiotic use compared to individuals who had remained antibiotic-free during the same time period (p<0.05). As serum concentrations of enterolactone are dependent on colonic conversion of plant lignans to enterolactone by the intestinal microflora (via beta-glycosidation), this study suggests infrequent antibiotic use has much longer-lasting effects on the microflora and its metabolic activities than was previously believed. (31) This negative association between serum enterolactone levels and antibiotic use has clinical importance due to recent studies showing correlations between high serum enterolactone concentrations and protection from cardiovascular mortality (32) and breast cancer. (33)

If an antimicrobial agent severely impacts the microflora, negative repercussions on host health can result, and include:

* Overgrowth of already-present microorganisms, such as fungi or Clostridium difficile. (34) Overgrowth of these organisms is a frequent cause of antibiotic-associated diarrhea, and overgrowth of C. difficile can develop into a severe life-threatening infection. (35)

* Decreased production of SCFAs, which can result in electrolyte imbalances and diarrhea. (36) Short-chain fatty acids play a vital role in electrolyte and water absorption in the colon. (37) Reduced production of SCFAs post-antibiotic use may be a causative factor in antibiotic-associated diarrhea. (38) Short-chain fatty acids also contribute to host health in other ways, such as improving colonic and hepatic blood flow, (39) increasing the solubility and absorption of calcium, (40) increasing the absorptive capacity of the small intestine, (41) and n3aintaining colonic mucosal integrity. (42)

* Increased susceptibility to intestinal pathogens due to the decrease in colonization resistance. (43) A decrease in colonization resistance after antibiotic administration has been observed in animal models. Such experiments have shown that disruption of normal microflora decreases the number of pathogens necessary to cause an infection and lengthens the time of infection. (44)

* Decreased therapeutic effect of some medicinal herbs and phytoestrogen-rich foods. (31) The activity of many medicinal herbs depends on bacterial enzymatic metabolism in the colon. Of the many enzymes produced by intestinal flora, bacterial beta-glycosidases probably play the most significant role, as many active herbal constituents are glycosides and are inert until the active aglycone is released via enzymatic hydrolysis. (45) Herbs such as willow bark (Salix spp.), senna (Cassio senna), rhubarb (Rheum palmatum), devil's claw (Harpagophytum procumbens), soy (Glycine max), and red clover (Trifolium pratense) would be essentially inactive without this colonic metabolism. (45,46) Based on the results of the above-described epidemiological study, (31) it can be inferred that antibiotic use interferes with microbial beta-glycosidation in the GIT for a considerable period post-antibiotic administration, which could significantly impact the efficacy of many phytotherapeutic agents prescribed post-antibiotic use.