The strategy seems to be working, according to the US Department ofAgriculture (USDA). In 1998, only 65 per cent of samples of pork intended for processing plants metthe 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), theAnimal 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 foodproduction. The research also aims to help smaller producers and processors, who usually do not havethe resources to conduct investigations themselves.
CAHFSE chose pork as its first food animal to research. During the initialtwo-year period, samples were taken from 48 farms across five states. FSIS also funded a pilot studyto 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 StateUniversity found that Salmonella infection in hogs waiting in pre-slaughter holding pens shot up 40per cent from about seven per cent after just a few hours.
"We need to find out which pathogens are moving from the farm to theprocessor and then on to retail," Fedorka-Cray stated in a USDA report highlighting theresearch.
Researchers are also doing detailed sampling, testing, and analytical work todetermine the on-farm and in-plant prevalence of Salmonella, Campylobacter, Escherichia coli, andEnterococcus bacteria.
"Because pathogens are fluid over time, we need to gather information overa long period-and across the production spectrum-to find out the impact any particular change inanimal health issues or plant operations will have," stated Fedorka-Cray.
So far, the data indicate how variable results can be over time. Thishighlights the importance of a continual sampling program on the farm and in the processing plantshe stated. For example, there are regional, seasonal, and farm effects in play. Sampling only onetime, as many studies do, only gives us a snapshot of events.
"CAHFSE gives us a history of events," she stated. "Oneother thing that certainly stands out is that resistance to antibiotics seems to beserotype-dependent. In other words, not all types of Salmonella become resistant to antibiotics thesame way. Some serotypes will be resistant to one antibiotic and not another. This makes studyingantibiotic resistance very complicated."
Meanwhile other USDA researchers are also working on cutting pathogen contamination in pigsdestined for the processing plant. In one study, microbiologist Thad Stanton and his team found thatnormal, commensal bacteria in the swine intestinal tract are not only reservoirs for microbialresistance, but are also, possibly, places where this resistance evolves.
Commensal bacteria feed off their hosts without harming them. Some offer protection frominfection by interacting with the host's immune system, while others directly benefit the host bydigesting feedstuffs and providing nutrients.
"One bacterium in particular, Megasphaera elsdenii, showed extremely high levels ofresistance to chlortetracycline, an antibiotic used to treat a variety of infections," statedStanton.
He is researching whether the bacterium can be used as a barometer species to evaluate managementstrategies and efforts aimed at reducing resistance among intestinal bacteria.
In other work, microbiologist Shawn Bearson and colleagues are using microarray technology andother techniques to take research on Salmonella in pigs to the molecular level. Microarrays aremicroscope slides containing bacterial or host DNA that make it possible to examine thousands ofgenes in a single experiment.
Bearson says she and others on the team want to identify the basis for swine's resistance tocolonization by S. enterica serovar Typhimurium by characterizing aspects of the animal's immunityto infection.
"Ultimately, we want to produce a genetic profile of the Salmonella-carrier pig," shestated.
Bearson says this will decrease preharvest disease and perhaps lead to diagnostic tests forresistance.
"The research will also help the pork industry in breeder pig selection and will helpcontrol reemergence of Salmonella on the farm and during transportation and marketing," shestated.