Auburn University graduate student Elle Chadwick, under the direction of Ken Macklin, is studying antibiotic-resistant salmonella serotypes that are known to cause foodborne infections in humans.
If the two-year salmonella study launched by Auburn University poultry scientist Ken Macklin were a sentence, you’d need two sheets of notebook paper to diagram it. It’s that complex.
The goal, however, is simple: to reduce the incidence of salmonella in ground chicken.
“According to 2012 USDA Food Safety and Inspection Service statistics, just 4.8 percent of broiler carcasses tested at processing plants are contaminated with salmonella, but at the same time, 28 percent of ground chicken tests positive for the bacteria,” Macklin says. “What that tells us is that the on-farm management practices and processing procedures that have been highly effective in reducing contamination in the whole bird aren’t working that well for ground chicken.”
It also strongly suggests the possibility that, in poultry, salmonella serotypes that are pathogenic to humans may settle in internal tissues or organs that subsequently may be incorporated into the ground product. That is the focus of Macklin’s research.
In his study, which is funded by a $124,275 U.S. Poultry and Egg Association grant, Macklin’s main objectives are to ascertain how and when chickens contract salmonella on the farm and which tissues serve as salmonella reservoirs in the birds.
“The salmonella that make people sick don’t make chickens sick, so a grower or processor can’t look at a chicken and tell that it’s infected,” Macklin says. “The results of our study should help poultry producers determine possible intervention strategies for reducing the risks of the bacteria entering the food chain.”
For the first year of the project, Macklin and Elle Chadwick, a graduate student working under Macklin’s guidance, are conducting what will be 10 five-week trials on two salmonella serotypes that are resistant to antibiotics and are known to cause foodborne infections in humans.
Each trial involves 100 day-old chickens placed in 10 cages, 10 to a cage. Over the course of the five weeks, the researchers “challenge,” or inoculate, the birds with one of the two serotypes, in one of three dosage levels, at one of three different stages of maturity and through one of six different pathways.
“One group’s only exposure to the bacteria, for instance, is through their feed,” Macklin says. “The other groups are infected through other routes, such as in the eye, into the stomach and under the skin.”
At the end of each trial, the birds are humanely euthanized, and Macklin and Chadwick collect and analyze tissue samples. Lots of samples.
“We take 14 tissue samples from every bird,” Chadwick says. “So for each trial, we aim to have at least 1,400 samples to analyze. By the end of the year, we will have looked at 14,000 samples.”
Year two of the study will entail crunching all the numbers from the 14,000 tests, interpreting those numbers and sharing that information with the industry in an effort to achieve the goal of reducing salmonella contamination in ground poultry.
Poultry products are by no means the sole source of pathogenic salmonella in the food supply, but of the more than 1 million reported cases of salmonella-related illnesses in the U.S. each year, 200,000, or 20 percent, are attributed to chicken and turkey.
Because salmonella occur naturally in the environment, realizing zero contamination in processed poultry is a pipe dream. But the poultry industry has made major strides in improving the safety of its products, largely through changes in processing techniques and performance standards. The 4.8 percent salmonella contamination rate of broiler carcasses mentioned above is evidence of that. Experts estimate that, in the 1970s, one of every two processed broiler carcasses tested positive for salmonella. By 1996, the contamination rate was down to 22 percent and by 2002, to 10 percent.
“There’s been an awful lot of progress in making poultry safer for consumers,” Macklin says. “And I’ll take this chance to remind consumers that, even if the chicken products they buy were to have any foodborne pathogens, proper cooking will take care of those.”
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