|Antibiotics may make fighting flu harder|
|Tuesday, 07 June 2011 00:00|
With winter on our doorstep and the flu knocking out workers left, right and centre, a new study by Yale University has shed light on the excessive use of antibiotics.
The highly respected international publication Science News magazine has reported on the study which found taking antibiotics when they aren’t necessary could make the flu or other viral infections worse.
Mice on antibiotics can’t fight the flu as well as mice that haven’t taken the drugs, say researchers from Yale. Antibiotics quash the immune system’s infection-fighting power by killing friendly bacteria living in the intestines, the researchers reported.
These friendly, or ‘commensal’ bacteria help defend against viruses by keeping the immune system on alert for viral invaders, the team discovered.
“There are a lot of beneficial effects of having commensal bacteria,” said Akiko Iwasaki, the Yale immunologist who led the study. “This is one that was unexpected, but makes sense.”
Scientists knew that friendly bacteria in the intestines could help stop disease-causing bacteria from setting up shop in the gut. And previous experiments hinted that gut microbes could influence how well the immune system worked, but researchers thought the effect was mainly confined to the digestive system.
“What’s fascinating about the new study is that there’s a distant regulation of resistance to viruses by gut microbiota,” said Alexander Chervonsky, an immunologist at the University of Chicago.
Lungs are normally sterile, so it was a bit of a surprise that killing bacteria as far away as the colon would have any effect on how well the lungs could fight viruses.
Iwasaki and her colleagues treated mice for a month with four antibiotics commonly given to people with bacterial infections, then infected the rodents with the flu. Antibiotic treatment impaired the mice’s ability to make an important flu-fighting molecule called interleukin-1 beta or IL-1 beta, the researchers found. IL-1 beta is necessary to combat influenza and other viruses.
Antibiotic-treated mice didn’t have generally weakened immune systems, though. The antibiotic-treated mice were still able to fight herpes, because the immune system fights off herpes and some other viruses using a different molecular weapon.
Gut bacteria are constantly priming the immune system to make IL-1 beta, keeping the immune system vigilant against the flu and other viruses. The researchers aren’t sure yet which bacteria in the gut are responsible for the virus-defence mechanism. “We know for sure that there are certain bacteria that can’t do it,” Iwasaki said. Sphingomonas bacteria, for instance, don’t stimulate the virus-fighting response.”
Some Lactobacillus bacteria, on the other hand, are known as ‘friendly’ gut bacteria and may play a role in virus defence. Mice treated with an antibiotic called neomycin, which wipes out most types of Lactobacillus bacteria while leaving Sphingomonas bacteria alone, have a hard time fighting the flu. If researchers can figure out which bacteria are responsible, it may be possible to make probiotics that will boost virus-fighting capabilities.