The misuse of antibiotics has already led to the emergence of a huge number of antibiotic-resistant bacteria that could potentially threaten the future health of the human species. As if that wasn’t bad enough, a new study in the journal Cell Reports reveals that mistakenly using antibiotics to try and treat the flu could make the illness up to three times more deadly, by disabling the body’s first line of defence against the virus.
This is because the bacteria in our gut are in fact the first responders to an invading flu virus, and get to work on destroying the unwanted pathogens long before our immune cells get mobilized. Yet as antibiotics interfere with our microbiota, these microscopic defenders become unable to ward off the virus.
According to the study authors, it takes two days for the immune system to detect the presence of the flu and start scrambling white blood cells to hunt down and destroy it. During this time, the virus hides in the lining of the lungs, where it multiplies.
However, bacteria in the gut use a type of signalling called type 1 interferon signalling to switch on an antiviral gene in the cells that line the lungs, causing them to release a protein that stops the flu virus from being able to multiply as quickly. This ensures that the flu’s viral army remains at a manageable size for the body’s immune cells to defeat when they finally join the fight two days later.
The researchers, from the Francis Crick Institute in London, treated mice with a course of antibiotics before infecting them with the flu virus. After two days, these mice were found to have five times more virus in their lungs than another group of mice that hadn’t been given antibiotics, due to differences in the health of their gut bacteria. As a consequence, only a third of the antibiotic-treated mice survived the flu, compared to 80 percent of those that hadn’t been treated.
When the researchers later repopulated the gut bacteria of the mice that had been given antibiotics, they found that this restored their ability to stop the virus from multiplying in the lungs during the first two days of infection, and enhanced their chances of recovering from the illness.
Commenting on these findings, study author Andreas Wack said in a statement that “antibiotics can wipe out early flu resistance, adding further evidence that they should not be taken or prescribed lightly.”