A step ahead
A CVM researcher recently built upon faculty research to track antimicrobial resistance
As a postdoctoral associate, Elizabeth Miller, PhD, tracked down antimicrobial resistance (AMR). Now a researcher in the lab of Tim Johnson, PhD, associate professor in the Department of Veterinary and Biomedical Sciences and director of research and development at the Mid-Central Research and Outreach Center, Miller’s previous research on antimicrobial resistant strains of E. coli in central Kenya has shown her tenacity for detail. As she investigated strains of antibiotic resistant E. coli in central Kenya, she hoped to find where the AMR originates in order to better predict how it is transmitted throughout an ecosystem.
AMR can be caused by a wide range of resistance genes in bacteria, which are becoming more prevalent as bacteria continue to evolve. “The AMR genes can either be in the bacteria’s chromosome and get passed down through generations,” says Miller, “or the bacteria can have them on mobile genetic elements (such as plasmids), which can be transmitted between bacteria.”
After receiving her PhD in disease ecology from the University of Notre Dame, Miller saw that Kim VanderWaal, PhD, assistant professor in the Department of Veterinary Population Medicine, was hiring a postdoctoral research associate at the University of Minnesota. VanderWaal’s PhD thesis, which Miller says inspired her own thesis at Notre Dame, was rooted in research she conducted in Ol Pejeta conservatory in Nanyuki, Kenya, where commercial cattle ranching and wildlife conservation are integrated. VanderWaal conducted novel research on how social interactions among the giraffes in the park influenced disease transmission. Energized by VanderWaal’s thesis and findings, Miller leapt at the chance to work for VanderWaal, and has been at the University of Minnesota College of Veterinary Medicine (CVM) since February 2017.
Since arriving at the CVM, Miller has been building upon this research to understand the prevalence of resistant E. coli in giraffes. Surprisingly, her most recent study suggests that Miller and her team were most likely to detect resistant E. coli strains in baby giraffes (neonates, ages 0-3 months).
Miller tested more than 150 adults and found only three with resistant E. coli in their systems. Only one juvenile out of the 15 Miller tested had a resistant string. Yet, four of the six neonates Miller tested carried a resistant strain of E. coli.
“Neonates don’t participate in social activities such as drinking from a central water source or eating grass in a communal field,” says Miller. “They are exclusively nursing from their mothers and we don’t have evidence showing that the mothers have the same resistant strains.” According to Miller, adults could actually be more likely to carry resistant E. coli strains, but the strains are just at levels too low for the team to detect. The strains are not having any evident effect on giraffe health, but their young are proving as helpful vessels for detecting the strains’ whereabouts. Resistant strains are not harmful unless they are pathogenic and cannot be treated with antibiotics. The increased likelihood that the scientists found of identifying resistant strains in giraffe neonates suggests that the microbial community in the neonatal gut is very different from that of older giraffes. “The neonates are sort of acting as sentinels of what AMR is in the giraffe population,” Miller says.
The researchers on this project did not find any evidence of resistant bacteria or gene transmission between giraffes. Additionally, the resistant bacteria have been previously found in E. coli from both humans and domestic cattle in East Africa. As such, the team determined that these resistance genes and resistant E. coli strains were most likely spilling over from humans or domestic animal sources. “What we humans are doing to domesticated animals has an impact on the environment,” says Miller.
Now that Miller has a better understanding of AMR in wild giraffes of Ol Pejeta, she says that the next step to take is looking at the isolates from the same study VanderWaal conducted for her PhD thesis that include E. coli from buffalo, black rhinos, lions, zebras, gazelles, wild dogs, and cattle in Ol Pejeta. Thanks to the bank of samples VanderWaal collected and the research Miller conducted, many questions can now be explored. “One option for a project is to look at the persistence in these other animals and compare it to what we are seeing in giraffes to better understand wildlife AMR and the role humans and domestic animals may be playing,” says Miller.
She says that researchers could also look at whether or not they are more likely to detect resistant E. coli in younger animals compared to older ones. “Additionally, we could think about differing diets between species—do species more likely to come into contact with humans and domestic animals have more AMR? Since we have E. coli from cattle, we could also compare E. coli strains from cattle to the strains we found in the giraffes, gazelles, or any of the other animals we have samples from. If AMR spillover is occurring, the strains would be the same,” she says.
According to Miller, the interdisciplinary nature of the CVM has helped her grow as a researcher more than she could imagine doing so in a more siloed work environment. “Because the U of M is such a big school, there are so many resources available. That’s been amazing for me,” she says. “I am an ecologist by training so coming to the College of Veterinary Medicine has been really beneficial because it helps me think about my research in a more applicable way. It helps me refine how I talk about ecology and the importance of it to a practicing veterinarian. I think all ecologists should encounter that—merging those two sides of veterinary medicine is really important.”