Researchers use conventional methods for salmonella detection

In the United States, poultry is responsible for more than one in every five cases of salmonella illness. According to a new study by the University of Georgia, typical methods of analyzing chicken from the grocery store will not be enough to identify all strains of the bacteria.

The research, which was published in Applied and Environmental Microbiology, looked at national salmonella records from the USDA Food Safety Inspection Service from 2016 to 2020.

Total cases of salmonella contamination in poultry declined from 9% in 2016 to 6.57% in 2020, according to scientists. During the same time, however, the number of people infected with salmonella in the United States remained steady.

When I first started at the Poultry Diagnostic and Research Center four years ago and met with several different poultry companies, one of the things they said to me was that the salmonella they find on the farms is not the same type of salmonella they find in the processing plant.

Nikki Shariat, Study Corresponding Author and Assistant Professor, College Of Veterinary Medicine, University Of Georgia

Because of this gap, it is difficult for the poultry industry to determine which varieties of salmonella to target with new vaccinations and other interventions aimed at reducing the amount of high-risk salmonella in the birds.

The scientists teamed up with the Georgia Poultry Lab Network in Gainesville, Georgia, to look at which salmonella serotypes were prevalent in breeder birds against those found in chicken products.

High-resolution technologies can inform effective salmonella control

The Kentucky serotype is the most common and easily identifiable strain of the bacteria on the farm in Georgia, accounting for 80% of all salmonella identified.

While there is no such thing as “good” salmonella, Kentucky is not known for causing human illness. Yet poultry firms appear to be better at removing Kentucky during processing, which could explain why the scientists did not find the same level of strain in the processed chicken.

They did find three other forms of salmonella in processing plant samples, including Infantis, Enteritidis, and Schwarzengrund, which are known to cause sickness in humans.

The question was, ‘where are these non-Kentucky serotypes coming from?’. We suspected they were present on the farm but that we were not able to detect them using traditional methodology.

Nikki Shariat, Study Corresponding Author and Assistant Professor, College Of Veterinary Medicine, University Of Georgia

Shariat’s team discovered various types of salmonella in live bird samples that previous approaches overlooked using technology she developed in 2015.

The tool, known as CRISPR-SeroSeq, finds molecular markers in salmonella’s CRISPR regions, a specialized section of the bacteria’s DNA, and aids scientists in determining which strains of the bacteria are the most common.

Over recent years, the poultry industry has made great strides in reducing salmonella in their processing facilities. There is no silver bullet that can eliminate salmonella in the processing plant or during pre-harvest in the birds.

Nikki Shariat, Study Corresponding Author and Assistant Professor, College Of Veterinary Medicine, University Of Georgia

Poultry veterinarians do vaccination against the forms of salmonella most commonly connected to human sickness outbreaks. However, in order to do so efficiently, vets must first determine which types of germs are present in the farm’s birds.

“The higher-resolution technology used in this research found that multiple salmonella serotypes were present but were typically outnumbered by serotype Kentucky,” Shariat said. “Our study now provides a framework for how to identify those serotypes. This knowledge provides poultry producers with better data to be able to inform their salmonella control practices.”

“Our main focus is to make sure that at the end of the day we’re facilitating improvements in the poultry industry,” said Amy Siceloff, study first author and a doctoral student in UGA’s Department of Microbiology. “Now that we’re aware of this gradual increase in serotypes and that they don’t just pop up overnight, this kind of surveillance is going to be key in managing salmonella moving forward.”