Traditional testing methods may not be sufficient to detect low levels of high-risk Salmonella


Poultry is responsible for more than one in five cases of salmonella infection in the United States. But traditional methods of testing the chicken you pick up off the grocery shelf may not be enough to detect all strains of bacteria, according to a new study from the University. from Georgia.

Posted in Applied and environmental microbiologythe study analyzed national salmonella data from the U.S. Department of Agriculture’s Food Safety Inspection Service from 2016 to 2020.

Researchers found that overall cases of Salmonella contamination in chicken increased from 9% in 2016 to 6.57% in 2020. But nationwide, cases of Salmonella infection in humans remained stable during this same period.

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


Nikki Shariat, corresponding author of the study and assistant professor at the College of Veterinary Medicine

This disconnect makes it difficult for the poultry industry to know which types of Salmonella to target with new vaccines and other interventions that can reduce the amount of high-risk Salmonella types in birds.

The researchers teamed up with the Georgia Poultry Lab Network in Gainesville, Georgia, to examine which strains of salmonella, called serotypes, were present in breeding chickens versus strains present in chicken products.

High-resolution technologies can inform effective salmonella control

The most abundant and easily detectable strain of bacteria on the farm in Georgia is the Kentucky serotype, accounting for 80% of all Salmonella found.

Although no salmonella is “good”, Kentucky is not commonly associated with human disease. And poultry companies seem to be able to remove Kentucky more efficiently during processing, which may be one reason researchers haven’t seen the same amount of strain in processed chicken.

What they saw in the processing plant samples were three other types of salmonella, some of which are known to cause illness in humans: Infantis, Enteritidis and Schwarzengrund.

“The question was, ‘Where did these non-Kentucky serotypes come from? ‘” Shariat said. “We suspected they were present on the farm but were unable to detect them using traditional methodology.”

Using technology developed by Shariat in 2015, his team found several strains of salmonella in live bird samples that traditional methods had missed.

Known as CRISPR-SeroSeq, the technology identifies molecular signatures in the CRISPR regions of salmonella, a specialized part of the bacteria’s DNA, and helps researchers identify the most abundant strains of bacteria.

“Over the past few years, the poultry industry has made great strides in reducing salmonella in their processing facilities,” Shariat said. “There is no magic bullet that can eliminate salmonella in the processing plant or during pre-harvest in birds.”

Poultry veterinarians vaccinate birds against the types of salmonella most often associated with human outbreaks. But to do this effectively, veterinarians need to know what types of bacteria are found in farm birds.

“The higher resolution technology used in this research revealed that multiple salmonella serotypes were present but generally outnumbered the Kentucky serotype,” Shariat said. “Our study now provides a framework on how to identify these serotypes. This knowledge provides poultry producers with better data to help inform their Salmonella control practices.

“Our primary goal is to ensure that ultimately we facilitate improvements in the poultry industry,” said Amy Siceloff, first author of the study and a doctoral student in UGA’s Department of Microbiology. “Now that we are aware of this gradual increase in serotypes and that they are not appearing overnight, this type of surveillance is going to be essential for managing Salmonella in the future.”

The study was funded by a USDA-NIFA award to Shariat. Doug Waltman of the Georgia Poultry Laboratory Network is co-author of this study.

Source:

Journal reference:

Siceloff, AT, et al. (2022) Regional differences of Salmonella in broiler chicken production in the United States from 2016 to 2020 and the contribution of multiserovar populations to Salmonella surveillance. Applied and environmental microbiology. doi.org/10.1128/aem.00204-22.

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