In 2015, the Center for Disease Control and Prevention (CDC) reported a Salmonella outbreak that infected 192 people in five states. The CDC’s National Antimicrobial Resistance Monitoring System laboratory analyzed samples from 10 people infected in the outbreak. All 10 were infected with a strain of Salmonella that was resistant to multiple antibiotics.
Researchers at the University of Minnesota Center for Animal Health and Food Safety (CAHFS) are working with the University of Minnesota Veterinary Diagnostic Laboratory (VDL) and the Minnesota Department of Health to learn which Salmonella strains are emerging in the Midwest.
Salmonella outbreaks in humans are linked to many sources, including swine—the source of the 2015 outbreak. Occasionally, well-adapted strains of antimicrobial resistant Salmonella emerge, infecting humans, animals, and other sources. These strains of Salmonella are on the rise, infecting the ecosystem and therefore posing a serious threat to human health.
The CAHFS and VDL partnership is using next-generation sequencing to decode the DNA of Salmonella samples collected from swine throughout Minnesota. Among the mass of data, they’re searching for genes associated with antimicrobial resistance (AMR).
And the project’s reach goes beyond Minnesota. The collaboration is sharing what they find with researchers who are studying Salmonella in animals and humans elsewhere in the world.
“Sharing our findings can help researchers and decision-makers understand if we're dealing with the same pathogens in different locations,” says Ehud (Udi) Elnekave, DVM, PhD, a veterinary epidemiologist doing a postdoctoral fellowship with CAHFS. “If those pathogens are being transmitted worldwide, we can anticipate pathways and better prevent the spread.”
The team is focusing on comparing the samples from swine with samples from humans, as well as environmental sources, to determine whether or not they are similar and, for example, whether or not a strain found in humans carries the same AMR potential as another found in livestock.
Better understanding how AMR spreads will help doctors, veterinarians, and food producers work together to prevent these bacteria from posing a serious threat to humans.
Through their sequencing, Elnekave and his team were able to characterize two genetically distinct groups within a newly emerging strain of Salmonella—one they have noticed is appearing in swine in the Midwest. They analyzed these two groups, looking for genes that resemble the ones scientists know to be AMR. In one of the groups, they found evidence of AMR genes.
The newly emerging strain of Salmonella currently circulating in swine in Minnesota is likely to be part of an emerging multidrug-resistant group first reported in Europe. It is genetically distinct from other strains of Salmonella and carries resistant genes that can potentially be transmitted horizontally, meaning they can cause other bacteria to become resistant as well.
If the team can identify the strains they sequenced as a match, the next step will be to figure out the transmission pathway of the strain between livestock, humans, or another source.
“We first need to understand what we are dealing with, characterize it, and then the next step would be to try to see if we can learn who's infecting whom,” says Elnekave.