Gut bacteria act as a first-line defence system for the lungs—and it's the lining of the lungs, and not the immune system as everyone assumed, that receive signals from the bacteria.
But these signals can get scrambled by antibiotics, and this makes the lungs more vulnerable to flu viruses, which can be more virulent as a result.
Researchers from the Frances Crick Institute in London infected laboratory mice with a flu virus; around 80 per cent of those with healthy gut bacteria survived, but this dropped to just 30 per cent in the ones that were first given an antibiotic.
It takes around two days for immune cells to respond to a flu virus infection in the lungs, but virus levels were five times higher in the mice given antibiotics.
This is yet more evidence that taking antibiotics isn't a decision that should be taken lightly, said researcher Dr Andreas Wack, and this also has ramifications in farming as livestock are often given antibiotics as a just-in-case prophylaxis.