Washington: Researchers have found that particular strains of a food-borne bug are able to invade the heart, causing serious and difficult-to-treat infections.
The bacteria Listeria monocytogenes is commonly found in soft cheese and chilled ready-to-eat products.
Listeria infections are usually mild, but for susceptible individuals and the elderly, it can infect the central nervous system, the placenta and the developing foetus, the Journal of Medical Microbiology reports.
About 10 percent of serious listeria infections involve a cardiac infection, says Nancy Freitag, associate professor of microbiology and immunology at the University of Illinois and principal study investigator.
These infections are difficult to treat, with more than one-third proving fatal, but have not been widely studied and are poorly understood, according to an Illinois statement.
Freitag and her colleagues isolated "an unusual strain, and the infection itself was unusual," she said. Usually with endocarditis (infection of the heart) there is bacterial growth on heart valves, but in this case the infection had invaded the cardiac muscle.
The researchers were interested in determining whether patient predisposition led to heart infection or whether something different about the strain caused it to target the heart.
They found that when they infected mice with either the cardiac isolate or a lab strain, they found 10 times as much bacteria in the hearts of mice infected with the cardiac strain.
Further, researchers found that while the lab-strain-infected group often had no heart infection at all, 90 percent of the mice infected with the cardiac strain had heart infections.
The researchers obtained more strains of listeria, for a total of 10, and did the same experiment. They found that only one other strain also seemed to also target the heart.