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Feedlot study hopes to help keep salmonella out of food

Feedlot study hopes to help keep salmonella out of food
Researchers examine why cattle from some feedlots test positive for salmonella and others test negative

Texas A&M AgriLife Research scientists are taking a closer look at salmonella in feedlots in effort to help develop pre-harvest food safety interventions and providing safe, wholesome food for consumers.

Related: Research Focused on Salmonella in Cattle Aims to Improve Food Safety

AgriLife Research scientists Drs. Jason Gill and Matt Taylor, along with other professors, are researching bacteriophages, or phages, which are viruses that act as predators to bacteria, for use as food safety interventions.

Both Gill and Taylor gave seminars recently to departmental faculty and graduate students on the findings from projects sponsored by the Beef Checkoff and Texas Beef Council.

Researchers examine why cattle from some feedlots test positive for salmonella and others test negative

Taylor described the recovery and identification of salmonella serovars from feedlot environmental samples, while Gill gave an overview of the presence and types of phages recovered from these samples.

Taylor and researchers looked to identify the serotypes of salmonella from environmental samples taken from a select group of feedlots in South Texas previously identified by study collaborators Drs. Kerri Gehring, Jeffrey Savell and Ashley Arnold, all in College Station, Texas, to bear differing rates of salmonella presence in the lymph nodes of cattle at harvest.

The work was published in the Journal of Food Protection. The researchers recovered no detectable salmonella from superficial cervical lymph nodes from cattle in one feedlot, while cattle sourced from feedlot B yielded 100% positive salmonella detection from cervical lymph nodes at harvest.

"These results led the research team to question what factors contributed to such dramatic differences in the presence of salmonella in cattle lymph nodes coming from these feedlots from within the same geographic region," Taylor said.

Related: FSIS Expands Salmonella Testing Program for Ground Beef

Gill suggested phages might be actively suppressing the indigenous salmonella in the one feedlot, while the other feedlot lacked phages capable of controlling salmonella populations.

The researchers in the current study, including graduate animal science research assistant Yicheng Xie, collected samples from feces, feed, drinking water and soil in pens.

"Those samples were processed in the Food Microbiology Laboratory and Texas A&M Center for Food Safety where salmonella was positively identified," Taylor said.

Of all the samples, 85% of recovered salmonellae were collected from a single feedlot, with the remainder from a second feedlot. None were recovered from the feedlot previously testing negative for salmonella in lymph nodes of sourced cattle during harvest.


From a set of 38 isolates representative of salmonella–positive samples, Salmonella Anatum was the most frequently recovered serotype, according to the researchers. Salmonella Montevideo, Muenchen, Altona, Kralingen and Kentucky were also recovered.

These results are similar to those from other researchers around the U.S. also researching the transmission of salmonella in beef via lymph node carriage.

"Interestingly, recovered salmonellae did not display resistance to multiple types of antibiotic drugs, though resistance to streptomycin was frequently observed, as well as sporadic resistance to other drugs, including gentamicin sulfisoxazole," Taylor said. "Eighteen different phage isolates were recovered from the feedlot samples, some with lytic activity against a diverse set of salmonella serovars."

These data were recently presented at the 2015 Beef Industry Safety Summit meeting in Dallas, and the Texas Association for Food Protection meeting in Austin.

"One opportunity from the current data may be to develop new pre-harvest food safety interventions that reduce the numbers of salmonella on cattle hides at harvest by combining salmonella-attacking phages together to kill any salmonella on the animal prior to harvest, Taylor said. "Such interventions already exist for some pathogenic E. coli, such as E. coli O157:H7.

"While such an intervention for salmonella would be unable to attack all serotypes of the pathogen, interventions could be designed that work to reduce the serotypes of salmonella most frequently recovered from cattle, or rather those serotypes most frequently associated with human disease on fresh beef products. This would benefit not only Texas but also U.S. cattle producers and the beef industry in providing a safe, wholesome food for consumers."

Source: Texas A&M Agrilife

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