Prof. Birgitte Kallipolitis, of the University of Southern Denmark in Odense, and colleagues found that omega-3 fatty acids deactivate the genes responsible for the virulence of L. monocytogenes, leaving the bacterium vulnerable to attack.
"It's interesting that naturally occurring, completely harmless and actually healthy fatty acids can be used to suppress dangerous bacteria such as listeria," says Prof. Kallipolitis. "The long-term perspective is that it may prove possible to develop new treatment methods - not only against Listeria, but also against other dangerous bacteria that are currently resistant to antibiotics."
The researchers recently reported their results in the journal Research in Microbiology.
L. monocytogenes is a genus of Listeria bacteria. It is the cause of listeriosis, a potentially deadly infection that affects around 1,600 people and kills around 260 in the United States every year.
Pregnant women, elderly adults, and individuals with a weakened immune system are at greatest risk for listeriosis.
Eating foods contaminated with L. monocytogenes is the primary cause of infection. High-risk foods include unpasteurized milk and dairy products, soft cheeses such as feta and Brie, and pre-prepared deli meats.
Omega-3 'switched off' infection-causing genes
Listeriosis is currently treated with antibiotics, but studies have shown that L. monocytogenes is increasingly becoming resistant to these medications.
The new research suggests that omega-3 fatty acids have the potential to neutralize L. monocytogenes, hampering its ability to develop resistance and making it open to attack.
The researchers came to their findings by testing varying concentrations of omega-3 on L. monocytogenes in laboratory conditions.
They found that within 30 minutes of administration, low concentrations of omega-3 had an effect on L. monocytogenes that could lead to new treatments for listeriosis.
The fatty acid "switched off" certain genes that are responsible for the virulence of L. monocytogenes - that is, its ability to cause infection.
"Our theory is that the fatty acids do something to the PrfA protein so that it cannot switch on the virulence genes, and we're very interested in finding out what exactly is occurring," says Prof. Kallipolitis.
Letting the bacterium live 'might be a better strategy'
Prof. Kallipolitis notes that bacteria do not establish new survival strategies that make them resistant to attack unless their growth is threatened, so the fact that omega-3 did not kill L. monocytogenes might be a preferable outcome.
"Bacteria can develop resistance to attacks, and we have many examples of how this merely creates new and even bigger problems for combating them. It might be a better strategy to let them live and instead aim to neutralize their capacity to cause disease," she adds.
"Our study has shown that common, naturally occurring fatty acids can switch off the specific genes that make the listeria bacterium dangerous. We tested omega-3 fatty acids, and it took them about half an hour to neutralize the Listeria bacteria."
Prof. Birgitte Kallipolitis
The researchers hope that their findings fuel the development of new strategies to tackle Listeria and other bacteria that are becoming resistant to antibiotics.