Study compares salmonella rates in backyard, commercial poultry farm samples

In a comparison of differently sized poultry farms, researchers at North Carolina State University found that rates of Salmonella in fecal and environmental samples were more prevalent on larger commercial farms than on smaller backyard farms. 

Perhaps more importantly, multidrug resistance was found in Salmonella samples from both types of production systems, even though antibiotics are not used on backyard farms and are only used sparingly on commercial farms. 

The findings could help small and larger farms understand more about the spread of Salmonella in their respective systems.

“We wanted to look at backyard broiler farms; broilers are chickens that are raised for meat consumption rather than egg consumption,” said Jessica Parzygnat, an NC State Ph.D. graduate and first author of a paper describing the research. “Broiler chickens are the top consumed meat in the U.S. and the world, but there’s not much research on backyard farms, which are growing in popularity in the U.S.

“The Centers for Disease Control has been issuing warnings on Salmonella outbreaks from backyard poultry farms in the last several years, so we wanted to see what pathogens are on backyard farms but also compare that to commercial farms.”

Researchers tested 10 backyard and 10 commercial flocks. The smallest backyard flock was 22 birds and the largest was 1,000 birds; all backyard farm birds lived outdoors. Commercial farms, meanwhile, had tens of thousands of birds that lived indoors. 

The researchers tested bird fecal samples, as well as environmental conditions like litter, soil, and feeders, for the presence of Salmonella, in addition to other pathogens. Researchers also examined compost samples on backyard farms. 

“We tried to examine where Salmonella is prevalent on farms through testing bird fecal samples and also the environment around them,” Parzygnat said. “We found less Salmonella on backyard farms (19.1% of samples) than commercial farms (52.3% of samples). We expected that, because previous studies had shown low rates of Salmonella on backyard farms. At the same time, our rates of Salmonella in samples on backyard farms were higher than in other studies looking at backyard poultry in the U.S.

“Both types of farm managers need to be careful with their birds,” Parzygnat continued. “There’s a feeling that backyard birds are safer than commercial birds, but even though we found less Salmonella, the proportion of Salmonella in backyard farms and commercial farms that were multidrug resistant – meaning that they showed resistance to three or more classes of antibiotics – was actually not significantly different.”

Parzygnat says that common-sense prevention measures can help consumers avoid Salmonella effects, including cooking chicken thoroughly and avoiding cross contamination while handling and preparing poultry. 

“Salmonella can be natural inhabitants of the bird gastrointestinal tract and the birds won't really show signs of illness,” she said. “I think one of the major concerns my research highlights is the antibiotic resistance associated with it because that really heightens the concern of infection.”

The paper appears in Foodborne Pathogens and Disease. NC State’s Sid Thakur is the paper’s corresponding author. Co-authors include Rocio Crespo, Mary Fosnaught and Lyndy Harden from NC State; Muhammed Muyyarrikkandy from South Dakota State University; and Dawn Hull from Walter Reed Army Institute of Research. Funding was provided by the USDA NIFA under SAS Grant 410553 and the FDA GenomeTrakr program under grant 5U19FD007113.

- kulikowski -

Note to editors: The abstract of the paper follows.

“Megaplasmids dissemination in multi-drug resistant Salmonella serotypes from backyard and commercial broiler production systems in the Southeastern United States”

Authors: Jessica L. Parzygnat, and Siddhartha Thakur, NC State University; Muhammed Muyyarrikkandy, South Dakota State University; Dawn Hull, Walter Reed Army Institute of Research 

Published: April 18, 2024 in Foodborne Pathogens and Disease

DOI: 10.1089/fpd.2023.0181

Abstract: Over the past decade, there has been a rise in U.S. backyard poultry ownership, raising concern for residential area antimicrobial resistant (AMR) Salmonella contamination. This study aims to lay the groundwork to better understand the persistence of AMR Salmonella in residential broiler production systems and make comparisons to commercial systems. Ten backyard and ten commercial farms were sampled at three-time points across bird production. Both fecal (n=10) and environmental (soil, n=5, litter/compost, n=5, feeder, and waterer swabs, n=6) samples were collected at each visit on days 10, 31, and 52 of production for backyard farms and days 10, 24, and 38 of production for commercial farms. AMR Salmonella was characterized phenotypically by broth microdilution and genotypically by whole genome sequencing. Overall, Salmonella was more prevalent in commercial farm samples (52.31%) over backyard farms (19.10%). Kentucky (ST 152) was the most common serotype found in both backyard and commercial farms. Multidrug-resistant (MDR, resistance to > 3 or more antimicrobial classes) isolates were found in both production systems, while ciprofloxacin and nalidixic acid resistant and intermediate isolates were more prevalent in commercial (33%) than backyard samples (1%). Plasmids that have been associated with MDR were found in Kentucky and Infantis isolates, particularly IncFIB(K)_1_Kpn3 megaplasmid (Infantis). Our study emphasizes the need to understand the selection pressures in disseminating megaplasmids in MDR Salmonella in distinct broiler production systems.