/ Sebastian Kaulitzki, AdobeStock.com
London – Lung infections with influenza are more often fatal in mice whose colon had been previously cleared of the bacterium by antibiotics. The reasons are according to a study in Cell reports (2019, doi: 10.1016 / j.celrep.2019.05.105) on the influence of intestinal bacteria on the release of interferons in the defense cells of the pulmonary mucosa.
The overuse of antibiotics not only promotes the development of a resistance that complicates the treatment of future bacterial infections. Antibiotics may also increase vulnerability to viral infections. This is suggested by experiments conducted on mice by researchers from the Francis Crick Institute in London.
Rodents whose intestinal flora is intact have survived about 80% of an experimental infection with the influenza virus. If the animals had already been treated with antibiotics for several weeks, the survival rate would have dropped to one-third. The virus concentrations in the pulmonary epithelium were then 5 times higher. The survival of the animals increased when the intestinal flora was restored by a stool graft.
The reason has suspected the team around Andreas Wack of an influence of intestinal bacteria on the formation of type 1 interferons. These proteins prevent the replication of viruses in the cells and form a first line of defense against infections (the subsequent antibodies take care of this task). Antibiotic therapy reduces the formation of type 1 interferons and increases again after stool transplantation.
The researchers initially suspected that the protective effect of intestinal flora was mediated by immune cells that reach the intestine through the circulation in the lungs. But they found no evidence of that. The production of type 1 interferons occurs directly in the epithelial cells. The way signals are transmitted from the intestine to the lungs is not yet clear.
The results of animal studies do not determine to what extent the mechanism also works in humans and whether antibiotic treatment can actually increase influenza. This would require epidemiological studies. For example, they might determine whether children treated with antibiotics in the first years of life have more frequent and more severe respiratory tract infections. If this were the case, the frequent use of antibiotics would eventually create the problems they are used to remedy.
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