Study finds resistant Salmonella in more animal than plant products

Published on February 01, 2017
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A decade of data on outbreaks of Salmonella infections indicates that Salmonella bacteria were more likely to be drug-resistant when they came from animal products than from plant products, a scientific article states.

A research team from the Centers for Disease Control and Prevention, in examining U.S. outbreaks from 2003-2012, found that 90 outbreaks had a single identified source. Plant products and animal products each were responsible for half of 68 pan-susceptible strains—those likely to respond to treatment with the antimicrobials tested—but 16 of 22 drug-resistant strains came from animal products.

“Our findings are consistent with other studies that show the use of antimicrobials in food animals can select for antimicrobial-resistant bacteria and that these resistant bacteria can cause resistant infections in people,” the article states.

“Whether a food was more frequently associated with resistant outbreaks can be explained, in part, by the ways in which antimicrobials are used in food production.”

The study results, published online Dec. 6, 2016, ahead of print in Epidemiology & Infection, indicate that, of the outbreaks caused by drug-resistant Salmonella bacteria, eight came from poultry, six from beef, two each from herbs and seeded vegetables, and one each from dairy, fruit, pork, and grains/beans.

The authors linked outbreak information submitted to the Foodborne Disease Outbreak Surveillance System with isolate susceptibility data in the National Antimicrobial Resistance Monitoring System.

“Our study is the first to link data from two national enteric disease surveillance systems to characterize the food sources of outbreaks caused by antimicrobial-resistant Salmonella,” it states.

The article also indicates all drug-resistant strains found in beef and most in poultry were resistant to multiple antimicrobials. Severe infections during outbreaks also were more often associated with drug-resistant Salmonella bacteria.

The article notes that, among other limitations, outbreak-associated infections account for a small fraction of Salmonella-related illnesses, half of outbreaks were not attributed to a single food source, and the available information was insufficient to show causal associations between farm practices and resistance development.

The authors work for the CDC in the Division of Foodborne, Waterborne, and Environmental Diseases. Their article, “Antimicrobial resistance in Salmonella that caused foodborne disease outbreaks: United States, 2003-2012,” is available here.