LSU Researcher Tackles Food Safety in Produce
March 3, 2010 – A quick way to test for
Salmonella in vegetable fields may be in the offing if research by an LSU
AgCenter scientist proves its worth.
Working under a $40,500 grant from the Center for
Produce Safety at the University of California, Davis, Beilei Ge in the
Department of Food Science is developing a test for contamination by
food-borne pathogens in produce bound for the retail marketplace.
Ge is evaluating a process that samples Salmonella using
a technique scientists call DNA amplification, which increases the volume of
the DNA to a level high enough to detect easily. As one of the most common
causes of food-borne disease outbreaks, Salmonella is responsible for an
estimated 1.4 million annual cases in the United States according to the
U.S. Centers for Disease Control and Prevention.
The process tests samples of fruits and vegetables for
the presence of DNA linked to certain disease-producing microorganisms,
generally referred to as pathogens. Current tests use a technique called PCR
– or polymerase chain reaction – that detects Salmonella based on DNA, Ge
LSU AgCenter researchers have been developing and
evaluating a novel isothermal – one constant temperature – method to amplify
certain genes. Similar to PCR, this technique starts with efficiently
amplifying the target bacterial genes, duplicating the initial gene millions
of times in about an hour.
“The ability to quickly and accurately detect the
presence of even low levels of harmful microbes is essential for food safety
and biosecurity,” Ge said. “An ideal detection method is rapid, sensitive,
specific and cost-effective.”
Currently, food-borne pathogen detection relies heavily
on conventional microbiological culturing techniques, which are
labor-intensive and time-consuming, she said. Although newly developed
molecular techniques have improved performance, they still lack sensitivity,
take a long time for analysis or require expensive equipment.
The widely used PCR process measures all DNA, and the
results can’t differentiate between live and dead Salmonella cells so it may
give false-positive results. In addition, PCR requires designated laboratory
equipment that takes samples through several cycles of changing temperatures
over several hours.
“PCR tests have to be sent to a lab and often return
false positive results because they can’t determine between live and dead
Salmonella,” Ge said.
Ge is working with a novel isothermal process which was
developed in Japan and is beginning to gain momentum in the United States.
Her LSU AgCenter lab is one of the first U.S. labs to adopt the technique.
The novel DNA amplification process Ge uses requires
only one temperature – about 150 degrees – and the test can be done within
an hour. While the PCR technology requires the produce sample be sent to a
laboratory, Ge said, the technology has the potential to be used in the
Additionally, Ge’s technique measures only DNA from
live Salmonella. She uses a chemical that “binds” the DNA in dead cells so
it isn’t detected by the test.
chemical is quite specific for dead Salmonella cells but not live ones,” she
By combining these two elements – the novel DNA
amplification method and a novel chemical compound – Ge’s approach will be
able to develop a new way to identify Salmonella in produce.
“The test results are visual,” Ge said. “You can tell
by the turbidity of the sample whether you have a positive result. It also
reacts to a dye and gives fluorescence to identify contaminated samples.”
Ge is inoculating produce – cantaloupe, tomatoes and
spinach – with Salmonella and then checking how well the test can identify
the pathogen. Her next step will be to test the process in production
“We’re currently evaluating the process in the
laboratory,” she said. “We’re looking at how sensitive and specific the
results can be.”
Because a test does not require complicated equipment
and sophisticated technical skill, a field test would be feasible, she said.
During her five years with the LSU AgCenter, Ge has used
novel molecular detection assays to detect different bacterial pathogens.
The current Salmonella detection project is a collaboration with John
Beaulieu, a plant physiologist with the U.S. Department of Agriculture’s
Southern Regional Research Center in New Orleans.