A study examining the presence of salmonella in beef cattle feedyards was the focus of a series of studies by Texas A&M AgriLife Research scientists and faculty in the department of animal science at Texas A&M University, College Station. The findings could help develop new pre-harvest food safety interventions in providing safe, wholesome food for consumers.
AgriLife Research scientists Drs. Jason Gill, Dr. Matt Taylor and 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. 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.
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 percent 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.
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.
Taylor said the laboratory work utilized equipment from Roka Bioscience Inc.’s Atlas System at the Texas A&M Center for Food Safety in College Station. More information about the Atlas System technology and the collaboration between Roka Bioscience and Texas A&M can be found at http://bit.ly/1BUIUUX.
Of all the samples, 85 percent 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. In a comparison of culture plus biochemical-based detection of salmonella versus the Atlas System, test results yielded only one disagreement, where the single discrepant result was between an Atlas negative and a culture positive.
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.”