A genetic analysis of thousands of strains of the bacteria that causes listeriosis, a serious foodborne illness, is reported online this week in Nature Genetics. The study identifies strains that are more likely to cause disease and finds previously unknown factors that the bacteria use to infect individuals and cause disease, which could lead to better surveillance of this pathogen.
Listeriosis is a serious infection contracted by eating food contaminated with Listeria monocytogenes. It is particularly dangerous for pregnant women, as it can cause miscarriage or life-threatening disease in the newborn. However, listeriosis is also a significant concern for older adults, newborns and people with compromised immune systems. All strains of the bacteria are currently considered to be equally virulent, or disease causing, by regulatory bodies.
Marc Lecuit, Sylvain Brisse and colleagues collected 6,633 strains of L. monocytogenes from clinical samples and foods and combined this diverse sample set with medical data from patients with listeriosis to determine which strains found in food were most likely to cause disease. They also identified strains that cause disease in people with fully functioning immune systems, which indicates that these bacteria are more virulent because they can evade the immune system. The authors compared the genomes of 104 strains representative of the diversity in their sample and identified genes specific to the virulent strains. One new group of genes, named LIPI-4, is likely involved in the bacteria's ability to infect the central nervous system.