Unraveling the Listeria Genome

If knowledge is power, Agricultural Research Service scientists are gaining the upper hand on Listeria monocytogenes.

Researchers at the ARS Eastern Regional Research Center (ERRC) in Wyndmoor, Pennsylvania, and the Institute for Genomic Research in Rockville, Maryland, sequenced four strains of Listeria related to foodborne listeriosis outbreaks—an important step toward developing a management strategy for this deadly bacterium.

“Researchers in the ERRC Microbial Food Safety Research Unit have completed whole genome sequencing and comparison of four genomes, which allowed us to significantly improve our understanding of Listeria,” says research leader John B. Luchansky. In addition to finding serotype-specific and strain-specific genome sequences, they found that these four Listeria strains have largely similar genetic content and organization.

The team believes a few unique regions could account for epidemiological and antigenic differences among strains. Understanding these differences will improve scientists’ ability to assess the risk posed by contamination of food by this bacterium.

They also confirmed that Listeria bacteria have 15 genes in a regulatory protein family known as “Crp/Fnr,” considerably more than most bacteria have. Luchansky and molecular biologists Darrell Bayles and Gaylen Uhlich are investigating whether these sequences influence the bacterium’s virulence or persistence in the food supply.

The scientists have estimated the percentage of the genome for which there is no known function and identified specific genes that warrant further investigation. They’ve also started to pursue proteomics and genomics studies, Luchansky says. This involves comparing different strains of bacteria—or the same strain growing under different environmental conditions—to determine whether there are differences in the level of gene or protein expression under the conditions tested.

Knowing more about the bacterium will enable regulatory agencies and the food industry to make better informed decisions about safety standards and control strategies, Uhlich says. And uncovering the genetic information that defines Listeria’s survival, growth, persistence, and ability to cause disease will help scientists better understand the bacterium’s virulence, its presence in the environment, and its persistence in the food chain.

“Ultimately, we hope to learn enough about Listeria to prevent contamination, decrease prevalence, and reduce disease,” Bayles says. “This research puts us in a better position to make scientifically sound decisions about managing the threat of foodborne listeriosis.”—By Laura McGinnis, Agricultural Research Service Information Staff.

John Luchansky, Darrell Bayles, and Gaylen Uhlich are with the USDA-ARS Eastern Regional Research Center, 600 E. Mermaid Ln., Wyndmoor, PA 19038-8598; phone (215) 233-6620 [Luchansky,] (215) 233-6678 [Bayles], (215) 233-6740 [Uhlich], fax (215) 233-6581.

"Unraveling the Listeria Genome" was published in the October 2006 issue of Agricultural Research magazine.