http://www.dreamstime.com/royalty-free-stock-images-chicken-farm-image24069509Despite Salmonella being the most common illness-causing foodborne bacteria in the U.S. food system, still very little is known about the precise processes through which the bacterium contaminates and transmits among its most pervasive carriers: chickens. New research from the University of Arkansas, however, is aiming to bridge the gap in knowledge about how Salmonella infects such a large percentage of poultry. If the researchers can map out the process, food safety scientists stand a better chance of developing a method to stop it in its tracks and keep it from spreading, said Yichao Yang, lead researcher of the study and a doctoral candidate at the university’s Department of Poultry Science. To reach the goal of clearly mapping out the Salmonella transmission process within flocks, Yang has designed a novel testing scheme. The tests are still in their preliminary stage, she told Food Safety News, but they are already seeing some interesting results. Using six unique strains of Salmonella with a specific DNA identification code, and a group of initial carrier chicken for each of the unique strains, the researchers worked to map out how the bacteria moved through a Salmonella-free flock. So, the groups of carrier chickens were infected with the bacteria via one of three methods: orally (direct, with half given high doses and half low doses), through feed (half the strains added at high doses, the other half at low doses), or through the water supply (also at half high, half low doses). The infection groups were separated by these methods, with six chickens in each group. In other words, six chickens were infected orally, another six were infected in their feed, and yet another six were infected through their water supply. And each specialized strain of Salmonella had DNA “barcode” that the researchers could follow as it interacted with the the flock. Each group of six infected chickens were then placed with additional 10 Salmonella-free peers, making flocks of 16, ready to share their barcoded bacteria with one another. In the oral transmission group, the non-infected birds appeared to only become infected with one strain of Salmonella that was given in a high dose. But if the chicken was infected by a low dose of Salmonella, it then became infected with additional strains.  The other two groups had a notably different result. The Salmonella strains given in high doses initially infected the chickens first in equal proportions. As time went on, however more of the low dose Salmonella entered into the flock, and the strains began to share an equal foothold among the flock. The research team is still working to map out exactly how each infection spread and plans to conduct further trials with larger flocks. In the meantime, they’ve made at least one novel discovery: Chickens can be infected with more than one strain of Salmonella. Previously, research into Salmonella in flocks suggested that once a chicken was colonized by one strain of Salmonella, that strain would prevent others from further colonizing the bird. This is known as the colonization inhibition theory, Yang said. But, according to this research, chickens can indeed be infected with more than one unique strain. Knowing that their preliminary study is already leading to new discoveries related to Salmonella transmission in flocks has made Yang and her team even more optimistic about making further discoveries. The eventual goal is helping to reduce the spread of Salmonella to chickens and, further down the line, humans. “If we know exactly how Salmonella transmits in chickens, we’ll be able to know how it’s coming into the flock,” Yang said. “We believe we can stop the transmission if we know how it occurs and therefore stop transfer into the human food chain.”

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  • Carl Custer

    A nifty paper to read is Foley, et alia. 2011. Population Dynamics of Salmonella enterica Serotypes in Commercial Egg and Poultry Production. Appl. Environ. Microbiol. 2011, 77(13):4273-4279. It should be free since it’s over a year old.