FoodProductionDaily, USA, France
10-24-06
Research helps cut Salmonella contamination
By George Reynolds
Government researchers are helping to dramatically reduce Salmonella on pig
farms, part of a bid by the US agriculture department to prevent the pathogen
from showing up at processing plants.
The strategy seems to be working, according to the US Department of
Agriculture (USDA). In 1998, only 65 per cent of samples of pork intended for
processing plants met the USDA's minimum standards for Salmonella
contamination. Since then, work by a number of USDA agencies, which
combined efforts in 2003, has helped to push the pass rate beyond 90 per cent in
2005.
Pathogens such as Salmonella can can spark off an expensive recall for a food
company, which would also have to deal with damage to its brand and the
subsequent loss of sales.
The work is being done by USDA's Agricultural Research Service (ARS), the
Animal and Plant Health Inspection Service (APHIS), and the Food Safety and
Inspection Service (FSIS), which joined forces to create the Collaboration in
Animal Health and Food Safety Epidemiology (CAHFSE) program.
CAHFSE was set up to routinely track critical diseases in animal food production.
The research also aims to help smaller producers and processors, who usually
do not have the resources to conduct investigations themselves.
CAHFSE chose pork as its first food animal to research. During the initial twoyear period, samples were taken from 48 farms across five states. FSIS also
funded a pilot study to collect samples from pork-processing plants to be sent for
analysis.
“It's important to compare microbial data from both the farms and the processing
plants to determine the impact each has on movement of pathogens,” said USDA
researcher Paula Fedorka-Cray. “The data can also give information about the
effects of plant operating speeds and temperatures on pathogen occurrence in
swine."
A study by the National Animal Disease Centre (NADC) and Iowa State
University found that Salmonella infection in hogs waiting in pre-slaughter
holding pens shot up 40 per cent from about seven per cent after just a few
hours.
“We need to find out which pathogens are moving from the farm to the processor
and then on to retail,” Fedorka-Cray stated in a USDA report highlighting the
research.
Researchers are also doing detailed sampling, testing, and analytical work to
determine the on-farm and in-plant prevalence of Salmonella, Campylobacter,
Escherichia coli, and Enterococcus bacteria.
“Because pathogens are fluid over time, we need to gather information over a
long period—and across the production spectrum—to find out the impact any
particular change in animal health issues or plant operations will have,” stated
Fedorka-Cray.
So far, the data indicate how variable results can be over time. This highlights the
importance of a continual sampling program on the farm and in the processing
plant she stated. For example, there are regional, seasonal, and farm effects in
play. Sampling only one time, as many studies do, only gives us a snapshot of
events.
"CAHFSE gives us a history of events," she stated. "One other thing that
certainly stands out is that resistance to antibiotics seems to be serotypedependent. In other words, not all types of Salmonella become resistant to
antibiotics the same way. Some serotypes will be resistant to one antibiotic and
not another. This makes studying antibiotic resistance very complicated.”
Meanwhile other USDA researchers are also working on cutting pathogen
contamination in pigs destined for the processing plant. In one study,
microbiologist Thad Stanton and his team found that normal, commensal bacteria
in the swine intestinal tract are not only reservoirs for microbial resistance, but
are also, possibly, places where this resistance evolves.
Commensal bacteria feed off their hosts without harming them. Some offer
protection from infection by interacting with the host's immune system, while
others directly benefit the host by digesting feedstuffs and providing nutrients.
“One bacterium in particular, Megasphaera elsdenii, showed extremely high
levels of resistance to chlortetracycline, an antibiotic used to treat a variety of
infections,” stated Stanton.
He is researching whether the bacterium can be used as a barometer species to
evaluate management strategies and efforts aimed at reducing resistance among
intestinal bacteria.
In other work, microbiologist Shawn Bearson and colleagues are using
microarray technology and other techniques to take research on Salmonella in
pigs to the molecular level. Microarrays are microscope slides containing
bacterial or host DNA that make it possible to examine thousands of genes in a
single experiment.
Bearson says she and others on the team want to identify the basis for swine's
resistance to colonization by S. enterica serovar Typhimurium by characterizing
aspects of the animal's immunity to infection.
“Ultimately, we want to produce a genetic profile of the Salmonella-carrier pig,”
she stated.
Bearson says this will decrease preharvest disease and perhaps lead to
diagnostic tests for resistance.
“The research will also help the pork industry in breeder pig selection and will
help control reemergence of Salmonella on the farm and during transportation
and marketing,” she stated.