Study reveals resistance to several commonly used antibiotics, prompting further research into how resistance may spread through Indiana waterways
Bacteria collected from Indianapolis' Eagle Creek Reservoir are giving Marian University researchers a closer look at one of the world's growing public health challenges: antibiotic resistance.
In a study published in September, researchers found that all 72 bacterial isolates they tested were resistant to at least one antibiotic. More than half were resistant to imipenem, a powerful antibiotic often used to treat serious infections when other medications fail.
The findings, published in Marian University's Beyond the White Coat research journal, raise important questions about how antibiotic resistance develops and persists in the environment and whether the genes responsible could spread among different bacterial species.
"Honestly, several things surprised us, and they're more striking together than separately," said Samina Akbar, Ph.D., professor of microbiology and chair of Biochemistry, Microbiology and Immunology at Marian University.
One finding stood out in particular: 51.4% of the bacterial isolates were resistant to imipenem, an antibiotic in a drug class often reserved for severe infections.
"That rate is higher than what comparable reservoir studies have reported, and it was the finding we most wanted to look at more closely," Akbar said.
Why antibiotic resistance matters
Antibiotics are essential medicines used to treat bacterial infections. But some bacteria can survive exposure to antibiotics that would normally kill them or stop their growth.
When bacteria develop resistance to multiple antibiotics, infections caused by those organisms can become more difficult to treat. Antibiotic resistance is recognized worldwide as a serious and growing public health challenge.
Although antibiotic resistance is often associated with hospitals and healthcare settings, resistant bacteria can also be found in the environment.
Rainwater runoff, agricultural activity, and wastewater can carry bacteria and antibiotic residues into rivers, lakes, and reservoirs. Once there, resistant bacteria may encounter other microorganisms, creating opportunities for resistance genes to persist or potentially spread.
Eagle Creek Reservoir, which receives runoff from surrounding urban and agricultural areas, provided Marian researchers with an opportunity to investigate those patterns close to home.
The research team collected water from four locations within the reservoir and isolated 72 bacterial isolates of Gram-negative bacteria, a broad group that includes both harmless environmental organisms and bacteria capable of causing infections.
The researchers tested the isolates against 17 antibiotics.
On average, each isolate was resistant to more than five of those drugs. Two isolates showed resistance to 13 of the 17 antibiotics tested.
Researchers also discovered that resistance to different antibiotics frequently occurred together.
That observation has become a major focus of the next phase of their investigation.
How resistance could spread
Bacteria can carry antibiotic resistance genes in different ways.
Some genes are located on a bacterium's chromosome, which contains its primary genetic instructions. Others may be carried on smaller pieces of DNA called plasmids.
The distinction matters because plasmids can sometimes move from one bacterium to another, potentially transferring antibiotic resistance along with them.
Researchers found that resistance to antibiotics from unrelated drug classes frequently appeared together in the Eagle Creek samples.
"When resistance to unrelated drugs travels together that often, it suggests the genes may be linked on mobile genetic elements such as plasmids or integrons," Akbar explained.
In simpler terms, several forms of antibiotic resistance may be connected genetically, allowing them to move together rather than independently.
That possibility matters because a single transfer could give another bacterium resistance to multiple antibiotics.
But Akbar emphasized that the researchers have not yet established whether those genes are carried on transferable genetic material.
"We haven't confirmed that genetically yet, but it is the pattern that most shaped our plans for the next phase of the work," she said.
Undergraduate students are now examining bacterial isolates for plasmids, while selected samples have been sent for genetic sequencing. The work will help researchers identify the bacteria and better understand the mechanisms behind their resistance.
Marian students contribute to research
Marian University osteopathic medical students Cameron Brooks, Ahmed Farid, Danielle McKinzie, and Dayne Ousley, along with Akbar, authored the published Eagle Creek study.
Their work is part of a broader research effort examining antibiotic resistance in central Indiana waters.
Researchers have collected water and isolated bacteria from Eagle Creek, Geist, and Morse reservoirs, as well as the EcoLab, a body of water adjacent to Marian University's campus. Sampling at Lake Monroe is planned for next summer.
The next phase will investigate whether resistance genes are located on bacterial chromosomes or on plasmids, and whether multiple resistance genes are carried together.
By studying bacteria from several locations, the team hopes to better understand how resistance patterns may differ across Indiana waterways.
What the findings mean for the public
Despite the striking results, Akbar cautioned against drawing conclusions about the safety of Eagle Creek or other local waterways.
"It's too early to draw conclusions about risk, but these findings give us an important clue about what could be happening in Eagle Creek and in other urban reservoirs like it," she said.
The researchers have not yet identified all the bacterial species they tested or determined which resistance genes they carry. Some environmental bacteria are naturally resistant to certain antibiotics, and the study examined water collected during a single summer sampling period.
Most importantly, detecting antibiotic-resistant bacteria in water does not mean those bacteria are causing infections in people.
The findings also do not establish that treated drinking water is unsafe.
For people enjoying recreational activities such as swimming, fishing, and kayaking, Akbar recommends ordinary precautions, including avoiding swallowing reservoir water, covering open cuts, and washing after contact with the water.
The bigger question is whether waterways can serve as places where antibiotic resistance genes persist and potentially move between bacteria.
Future research will focus on identifying bacterial species, analyzing resistance genes and plasmids, and collecting samples across different seasons.
That information could eventually help scientists and public health officials determine where additional monitoring is needed and whether similar patterns are emerging in other reservoirs.
"Our study can't answer that yet, but it tells us where to look and what to look for," Akbar said.
Several Marian University undergraduate and osteopathic medical students are continuing the research, building on the initial findings as the team works to better understand antibiotic resistance in Eagle Creek. For them, Eagle Creek is more than a familiar Indianapolis landmark. It's an opportunity to investigate a global health challenge in their own community and contribute to understanding how antibiotic resistance moves through the environment.
Research publication: Antibiotic Resistance of Aquatic Gram-Negative Bacteria within Metropolitan Areas: Indianapolis and the Eagle Creek Reservoir, published in Beyond the White Coat, Volume 2, September 2026.