By: Freya Preimsberger
In addition to being part of a healthy diet, fatty acids may also be able to neutralize a type of harmful bacteria that causes food poisoning. Biochemists and molecular biologists from the University of Southern Denmark have found that certain fatty acids, such as omega-3 fatty acids, can switch off the virulence genes of a species of bacteria in the genus Listeria. In the future, the findings may be used to help develop new ways of treating antibiotic-resistant bacteria and combatting food poisoning. The researchers published their findings in Research in Microbiology on March 23.
During infection, bacteria of the species Listeria monocytogenes are capable of crossing the intestinal, blood-brain and placental barriers, causing some of the severe complications associated with Listeriosis, the form of food poisoning it causes. The bacteria utilizes a transcription regulator named PrfA to regulate the virulence genes that code for the proteins that allow the bacteria to enter and infect host cells. Activation of virulence genes by PrfA mostly takes place in the bloodstream and during intracellular infection, rather than in the digestive tract, and is an important component of infection.
Previous studies already identified fatty acids as an antimicrobial compound for their ability to disrupt bacterial cell membranes. L. monocytogenes, being a foodborne pathogen, often encounter fatty acids while in their hosts’ guts. Although the mechanism is not clearly understood, previous studies found that fatty acids inhibited the expression of virulence factors in the bacteria responsible for cholera and salmonella poisoning. Researchers at the University of Southern Denmark set out to see how medium- and long-chain fatty acids, found in normal human diets and in bile, would affect L. monocytogenes. They found that subinhibitory concentrations of free fatty acids downregulated PrfA-activated genes, effectively neutralizing the bacteria. In the study, the fatty acids were able to “turn off” the bacteria’s virulence genes in as little as half an hour. The study included omega-3 fatty acids, which are part of a healthy diet and found in foods like salmon and flax.
Combined with further research, the findings may pave the way for the development of new compounds to fight foodborne infections. The fact that the bacteria are only “deactivated” and not killed may actually be advantageous, said the study’s lead author in a press release. When their survival is not at stake, the bacteria will not mutate and develop resistance to the compounds being used to treat them. The same researcher also said that, in the long term, it may be possible to incorporate fatty acids into the treatment of antibiotic-resistant bacteria.
Listeria are found in soil, water and animals and can contaminate dairy products and processed meats. In contrast to many other types of bacteria, Listeria can reproduce at low temperatures, such as in refrigerators. Listeriosis affects an estimated 1,600 people each year in the United States, 260 of which will die of infection. Most people who ingest the bacteria will not become ill, and those who do will usually only become slightly ill. Healthy people typically have mild symptoms, such as headache, fever, chills, other flu-like symptoms and diarrhea, while certain populations are more prone to severe symptoms and complications.
The groups more likely to become severely ill are pregnant women, the elderly, newborn babies and those with compromised immune systems. Pregnant women, for instance, have temporarily impaired immune systems and are more likely to develop Listeriosis, particularly in the third trimester of pregnancy. They will only have flu-like symptoms, like fever, headache, fatigue and muscle pain. However, the infection can spread to the fetus through the placenta and cause premature birth, miscarriage or a stillbirth; 22 percent of Listeria infections in pregnant women will result in a stillbirth or death of the fetus, according to one study. Newborns are also at risk of being infected during or after birth, and have a mortality rate of 25 to 50 percent after infection.
The elderly and those with compromised immune systems, such as those with AIDS, may suffer from severe complications and invasive infections. Listeria may spread to other parts of the body, such as to the skin, abdomen, eyes or skin. As mentioned above, the bacteria can cross intestinal and blood-brain barriers and cause serious complications which may result in death. Patients with invasive infections who are over the age of 50 have a 17.5 percent fatality rate. One of these invasive infections is sepsis, during which the bacteria spread to the bloodstream, and the body’s response to infection damages organs. Another complication is meningitis and encephalitis, during which the membrane surrounding the brain and brain tissue itself become inflamed. Listeria infection can also result in osteomyelitis, septic arthritis and prosthetic graft infections in susceptible populations. Invasive Listeriosis occurs much less often in healthy, young people. For those groups at a high risk of severe complications, diagnosing and treating the infection early are critical. Physicians diagnose Listeriosis through testing body tissues, blood samples, stool samples or spinal fluid. Invasive and severe infections are treated with antibiotics. Antibiotic resistance in foodborne pathogenic bacteria, including L. monocytogenes, is a growing concern, presenting another obstacle in treating foodborne illness.
The most common route of infection is through eating contaminated food. Listeria can grow in cold temperatures in the refrigerator and are best killed through cooking or pasteurization. According to the Centers for Disease Control and Prevention, outbreaks of Listeria in the 1990s were mostly linked to processed meats, such as hotdogs and deli meats. Most outbreaks today are linked to produce and dairy products, including ice cream, soft cheeses, cantaloupe and sprouts. In order to prevent infection, especially for those in at-risk groups, it’s recommended that you exercise food safety practices. Products containing unpasteurized milk should not be consumed and animal products should always be cooked to a safe internal temperature. Food surfaces should be washed thoroughly, especially after being used with uncooked foods. Produce should be rinsed thoroughly before being eaten. Animal products should be stored separately from other foods in order to prevent contamination. If you have questions on infection with Listeria, you can call 1-800-CDC-INFO for more information.