June 28, 2005
IFT Daily Newsletter
Listeria monocytogenes in ready-to-eat products can do quite a bit of damage even after several months in a starved state, according to new research results. Ramakrishna Nannapaneni, a food science research associate for the Univ. of Arkansas, has been exploring the issue for the Food Safety Consortium with a research team led by Mike Johnson.
ìThere has been a tremendous effort to find out virulence differences within Listeria monocytogenes for risk assessment needs,– Nannapaneni said, pointing to the bacterium’s damaged cells. ìThe next logical question is how long they remain virulent. That’s been the focus of our work.–

The Arkansas experiments tested Listeria monocytogenes cells that had been starved for 196 days and those that had not been starved. The healthy cells were strong enough to kill 90% of a target mouse cell population within two hours of release. The starved and injured cells, after more than six months of languishing, still had enough strength to kill 60% of their target cell population within six hours, then 90% of the target after eight hours.
ìIt’s important to understand how these starved cells are waking up and how to suppress them,– Nannapaneni said. ìThe long-term starved cells become smaller and coccoid, but they still remain viable and virulent.–