In order to understand how this pathogen can be so elusive and difficult to treat, a research team from Stanford University School of Medicine studied mice infected with Listeria. Their report published in the journal Disease Models & Mechanisms describes how they use a technique called in vivo bioluminescence to light up bacteria and allow them to see extremely tiny amounts of bacterial cells in living animals. Using this method, they found that small persistent patches of Listeria took up residence inside bone marrow in the mice. This is significant because it is thought that the bone marrow can act as a reservoir to the brain and spinal cord, potentially causing life-threatening infections, such as in bacterial meningitis in newborns.
Another interesting aspect of this study is due to the use of specially designed Listeria stains in treating cancer. Clinical trials are currently underway in which non-disease-causing strains of Listeria are administered to cancer patients to generate immune responses against tumors. The researchers thus also looked at these attenuated strains, and found that they too could be harbored in bone marrow. It is still unclear, however, if such bacterial persistence will increase or decrease therapeutic effects.
The study was undertaken by Jonathan Hardy, Pauline Chu, and Christopher H. Contag of the Stanford University School of Medicine.