Study lead author Sophia Kenney, postdoctoral scholar in the Department of Animal Science, samples a maternity pen for Salmonella Dublin. Credit: Penn State
Researchers at Penn State are sounding the alarm as Salmonella Dublin, a type of bacteria that can infect both cattle and humans, is becoming increasingly resistant to antibiotics. Some strains of the pathogen can cause severe illness and death in cattle and blood infections and hospitalization in humans.
According to the CDC, from 1996 to 2004, no strains of the pathogen were resistant to antibiotics. But from 2005 to 2013, more than half of Dublin infections became resistant to seven antibiotic classes, and clinical outcomes have worsened in recent years.
In her newest research, Sophia Kenney, postdoctoral scholar in the Department of Animal Science at Penn State, took a different approach to Salmonella Dublin than previous work. Past studies looked at specific sources such as only cattle, regions or time periods, but this study used all publicly available U.S. whole-genome sequenced strains from human, cattle and environmental strains.
“We wanted to get at the potential One Health dynamics of this pathogen in the U.S., a major beef and dairy producing country, by examining genomic differences and stability across strains from the different yet related sources and over time,” said Kenney.
In findings published in Applied and Environmental Microbiology, Kenney and team analyzed 2,150 samples of Salmonella Dublin collected from three sources—581 from sick cattle, 664 from sick humans and 905 from the environment in the U.S. from 2002 to 2023.
Using the publicly available data, the team looked for genetic components associated with enhanced pathogenicity, such as virulence and antibiotic resistance. They found that bovine strains had a higher prevalence of plasmid with multidrug resistance and the greatest genetic diversity, indicating more variation among cattle strains. But despite some of these genetic differences, data revealed the genetic core shared across all 2,150 strains of Salmonella Dublin was highly similar regardless of source. This similarity shows potential for cross-transmission between cattle, humans and the environment.
“That’s important because it shows that Salmonella Dublin is highly connected across humans, animals and the environment so efforts to control it need to consider all three,” said team leader and senior author on the study, Erika Ganda, associate professor of food animal microbiomes. “To tackle antibiotic-resistant Salmonella Dublin, we must use a One Health approach—looking at how humans, animals and the environment are interconnected in the spread and evolution of this dangerous pathogen.”
While the evolution of some Salmonella Dublin toward increased multidrug resistance is a concern, this study’s findings provide detailed genetic evidence that can help guide surveillance, such as better tracking of the bacteria and intervention strategies like limiting antibiotic use in livestock.