Antibiotics and the Gut Microbiome
Antibiotic therapies not only target specific microorganisms causing an infection, but they also the impact the microbial communities in the gut. Most antibiotics have broad-spectrum activity so they can be used to treat many diseases but the gut microbiota are also affected, with a potentially negative effect that may persist long after the antibiotics have been discontinued. Antibiotics can also trigger the growth of antibiotic-resistant bacteria strains which can act as a reservoir for resistance genes in the gut microenvironment.
Decreased diversity in the microbiome typically follows antibiotic treatment and some healthful bacteria are lost from the community indefinitely. which can leave detrimental effects. The antibiotic spectrum of activity and dose will influence the shift in gut microbiota composition and can lead to increased colonization and infection by opportunistic organisms such as Clostridium difficile and Candida albicans. Antibiotic-induced changes can also include alterations in the metabolites produced by the microbiota such as short-chain fatty acids. Short-chain fatty acids (SCFA) are beneficial for gut health because they serve as a primary food source for the microbiota and they are involved with water and electrolyte absorption and they help to maintain the intestinal barrier (see Leaky Gut).
In summary, a dysregulated, imbalanced gut microbime, whether induced by stress, antibiotics or other conditions can result in disruption of the immune system and lead to increased susceptibility to disease.
Dysregulation of the Gut Microbiota
Small Intestinal Bacterial Overgrowth (SIBO)
Small intestinal bacterial overgrowth (SIBO) is an example of a pathologic condition associated with dysregulation and impairment of the gut microbiota. SIBO is a condition in which the presence of excessive numbers of bacteria in the small bowel causes gastrointestinal symptoms including abdominal pain, bloating, gas, distention, flatulence, and diarrhea, present in more than two- thirds of SIBO patients. Some patients may also complain of fatigue and poor concentration
In severe cases, nutritional deficiencies including vitamin B12, vitamin D, and iron deficiencies can occur. However, no single symptom can be specifically attributed to SIBO. Symptoms often masquerade as other diagnoses such as IBS, functional diarrhea, functional dyspepsia, or bloating. This is due in part to the varied presentation of patients with SIBO and the number of underlying risk factors that can lead to SIBO. SIBO has been linked to diseases such as irritable bowel syndrome (IBS), inflammatory bowel diseases (IBD) including Crohn’s and ulcerative colitis, cirrhosis, fatty liver, postgastrectomy syndrome, and a variety of other conditions.
For example, in a patient with chronic pancreatitis, it may be difficult to conclude whether diarrhea results from pancreatic enzyme insufficiency or from coexistent SIBO. Similarly, in patients with Crohn’s disease, particularly those having undergone surgery, symptoms of abdominal pain, boating, and diarrhea could result from SIBO vs that of active inflammation, bile acid malabsorption, or postoperative strictures.
Several conditions such as intestinal dysmotility, altered GI anatomy, immune deficiencies, and reduced stomach acidity are predisposing factors for the development of SIBO.
While reduced stomach acidity can be a result of Helicobacter pylori colonization and aging, many people also take medications such as proton pump inhibitors (PPIs) to reduce their gastric acidity for stress ulcer prevention or gastric esophageal reflux disease (GERD). PPIs are known to alter the gut microbiota in 50% of patients on long-term treatment withPPIs. Although PPI duration is related to incidence of SIBO, there is a lack of knowledge regarding the appropriate or safe duration for taking PPIs.
Given the protective role gastric acidity has in regards to protecting against ingested pathogens, it is plausible that prolonged use of gastric acid suppressants may contribute to the incidence of SIBO and patients should be judicious in their use.
There are no universally accepted treatment approaches to treatment for SIBO. There are mixed reports of effectiveness for treatment with diet, antibiotics, probiotics and fecal transplantation.
The impact of the gut microbiome on health and disease is currently one of the most stimulating areas of medicine. Learning more about the gut microbiome may provide new treatment options for many conditions and diseases currently resistant to effective management including fibromyalgia, irritable bowel disease, Crohn’s, ulcerative colitis and autism.
The medical world is just beginning to learn about the gut microbiome, its role in dietary intake and disease development, and the effect of probiotic supplementation on various disease states.