New Tool on Tap for Fighting
Listeria By Jan
May 27, 2003
A new tool could be at hand for "subtyping" strains of
Listeria monocytogenes bacteria that cause food-borne illness, thanks to
scientists with the Agricultural Research
Subtyping determines the strain affiliation of Listeria
specimens isolated in the lab. This is critical to epidemiologists tracing
outbreaks back to their source, as well as to government and industry efforts
to safeguard food supplies through environmental monitoring, disinfection,
sanitation and other measures. In the United States, listeriosis sickens an
estimated 2,500 people annually, and kills 500. Of the bacterium's 13 known
strains, serotypes 1/2a, 1/2b and 4b are chiefly to blame.
In Pullman, Wash., ARS scientist Monica Borucki and
Washington State University scientists
Douglas Call and Thomas Besser devised a technique called mixed genome
microarray analysis to examine L. monocytogenes' DNA for genes that
differ among its strains. Identifying the genes will help the researchers learn
why some strains cause disease epidemics, while others don't, and help them
design subtyping methods for identifying the most pathogenic strains. These
methods could then be used to check for genetic evidence of the strains in
food, on farms or on food-processing equipment, according to Borucki, at ARS'
Animal Disease Research
Unit in Pullman.
In studies recently published in the Journal of Clinical Microbiology, the team
extracted DNA fragments from 10 representative Listeria strains. They
printed copies of them--in the form of hundreds of tiny dots, called microarray
probes--onto special microarray slides. Next, they used fluorescence to label
the DNA of the strains they wished to subtype, or genetically characterize. The
labeled DNA was then applied to the slide, where it bound to probes with
similar DNA. Computerized imaging software enabled the team to examine the
slides for DNA illumination patterns signaling the presence of subtype-specific
Eventually, the team hopes to parlay its microarray gene
discoveries into a fast, standardized method of subtyping that public health
labs can use to compare large amounts of data on strains that may cause local
and/or national epidemics.
ARS is the U.S. Department of
Agriculture's chief scientific research agency.