GI Flora Affected by Antibiotics—Leading to Allergies

Scientists from the University of Michigan Medical School found with experiments with laboratory mice, that changes in microbes of the GI tract brought on by antibiotic use can affect how the immune system’s response to allergens in the lungs.

”Antibiotics knock out bacteria in the gut, allowing fungi to take over temporarily until the bacteria grow back after the antibiotics are stopped. Our research indicates that altering intestinal microflorathis way can lead to changes in the entire immune system, which may produce symptoms elsewhere in the body,” according to Gary B. Huffnagle, Ph.D., an associate professor of internal medicine and of microbiology and immunology in the U-MMedicalSchool.

The research findings may help explain why over the last 40 years chronic inflammatory diseases, like asthma and allergies, have been increasing rapidly. The increase in these diseases corresponds to the increase in antibiotic use.
Everything that is inhaled is also swallowed. Every time you inhale, air flows past mucus-producing cells and tiny hairs designed to trap bits of pollen, dust and spores before they enter the lungs. The particles move into the stomach with saliva and mucus when you swallow. The immune system of the GI tract is exposed to these allergens, and cells called regulatory T cells are produced. These cells act to block allergic responses in the lungs and sinuses.

When antibiotics reduce the bacterial population in the GI tract, the number of yeast and other fungal organisms increase. In earlier studies, researchers discovered that fungi secrete molecules called oxylipins, which can control the type and intensity of immune responses.

Huffnagle says that this suggests the possibility that these oxylipins from yeast and fungi in the GI tract may prevent the development of regulatory T cells for swallowed allergens. The loss of regulatory T cells from the GI tract causeT cells in the lungs become sensitized to mold spores, pollen or other allergens. This may cause allergies or even asthma.

Mice were given a five-day course of oral antibiotics. The antibiotic dose was followed by a single oral introduction of the yeast, Candida albicans. Candidaalbicans is a yeast that is normally found in the GI tract. Increased growth of Candidiaalbicans is a common side-effect of antibiotics.

Two days after stopping the antibiotics – at a time when the gut bacteria were growing back  themice were exposed to Aspergillusfumigatus, a common mold. The mice were examined for the presence of an allergic response in the airways. Results were compared  between the mice that received antibiotics and those that did not.

‘Mice treated with antibiotics and colonized with Candidaalbicans showed hypersensitivity to A. fumigatus compared with mice that didn’t receive antibiotics. Every exposure to the allergen increased the inflammatory response.

Dietary antioxidants called polyphenols, which are found in fruits and vegetables, can limit fungal growth—and may improve allergic symptoms. A diet high in saturated fats and sugars slows the recovery of normal gut microflora—and may make allergies worse, according to Huffnagle. The Mediterranean diet is rich in sources of polyphenols, and Mediterranean-diet countries have lower rates of allergies, asthma and other inflammatory diseases than do countries like the United States, Canada and England, were more saturated fats and sugars, and fewer vegetables are consumed. It may be possible one day to prevent or treat allergies and inflammatory diseases with diet changes or supplements of ‘healthy’ bacteria, according to Huffnagle.