Healthcare experts worldwide are warning against the irrational use of antibiotics. Taking antimicrobials without a doctor's prescription, in the wrong doses, or for incomplete courses creates the conditions for bacteria to develop resistance. Doctors are increasingly reporting infections that are resistant to most modern antimicrobials. Furthermore, antibiotics can cause side effects, sometimes quite dangerous, so they should be used strictly as prescribed and never taken "just in case."

Recently, scientists discovered that taking antibiotics can significantly worsen the symptoms of the common flu. This was demonstrated by the results of a mouse study published in the journal Cell Reports.

As is well known, viral infections, including influenza, are not an indication for antibiotics. However, when a fever rises, people often start taking antibiotics "just in case," supposedly to prevent complications from viral infections. However, with influenza, taking antibiotics can increase the risk of death. This is because antibiotics suppress the body's first line of defense against viruses—the intestinal microflora (microbiota).

The immune system doesn't begin actively destroying the influenza virus immediately after the onset of the disease—it takes up to two days for lymphocytes to actively divide and destroy the pathogen. It's during these first days that bacteria living in the intestines play a key role in the body's defense. In the initial stages of the disease, the influenza virus replicates in the mucous membranes of the respiratory tract, particularly in the lungs. During this time, the intestinal microbiota, via the interferon type 1 signaling pathway, activates interferon synthesis in lung epithelial cells, which suppresses influenza virus replication. This keeps the number of viral particles within limits that the immune system can handle when it finally engages.

When taking antibiotics, intestinal microflora partially dies and its growth is suppressed, leaving the body defenseless against the virus, which, in turn, multiplies at a furious rate.

Researchers from the Francis Crick Institute in London compared the response of two groups of mice to influenza virus infection. The first group, unlike the second, received a course of antibiotics before infection. Two days after infection, the animals in the first group had five times more influenza virus in their lungs than the animals in the second group. Only a third of the mice in the first group recovered; the rest died. In the group of mice that did not receive antibiotics, 80% recovered.

When scientists transplanted microflora from animals that had not received antibiotics into animals that had received them, the former experienced activation of interferon in the lung epithelial cells and slowed down the replication of the influenza virus.

Thus, antibiotics can destroy the body's first line of defense against viruses, so their use in viral diseases is inappropriate.

* Konrad C. Bradley, Katja Finsterbusch, Daniel Schnepf et al. Microbiota-Driven Tonic Interferon Signals in Lung Stromal Cells Protect from Influenza Virus Infection // Cell Reports, 2019, 28 (1): 245-256. DOI: https: //doi.org/10.1016/j.celrep.2019.05.105