You’ve probably heard about antibiotic resistance in the news: bacteria are becoming resistant to antibiotic treatments, and we're not discovering new antibiotics at a fast enough pace.

What you’re hearing isn’t just talk.

According to the CDC, antibiotic resistance is an urgent global public health threat, killing at least 1.2 million people worldwide in 2019. More than 2.8 million antimicrobial-resistant infections occur each year in the United States—with more than 35,000 people dying as a result.

While antibiotic resistance is a topic that’s gaining attention, a similar but separate issue is often overlooked—antibiotic tolerance. These microorganisms aren’t antibiotic resistant, yet they still manage to survive treatments, continue growing within the host and cause persistent problems for those infected.

“We have a lot of infections that, in theory, should be able to be treated by antibiotics, but they are still difficult to treat,” said Dr. Austin Nuxoll, an associate professor in the University of Nebraska at Kearney’s Department of Biology.

Nuxoll has been researching Staphylococcus aureus (staph) since 2010 when he was a doctoral student at the University of Nebraska Medical Center and began studying antibiotic tolerance in 2014.

Tackling Persistent Infections

Many people have had an encounter with staph during their lifetime. People with children participating in sports like wrestling are a common example. Typically, you start putting the antibiotics on the infected area, and it'll go away.

Staph bacteria are usually harmless in the case of a skin infection, but if they enter the bloodstream or internal tissue, they can cause life-threatening infections. Preventing these threatening infections is critical, especially in a state like Nebraska that has an aging population. More than 25 percent of Nebraska’s population will be over the age of 60 by the year 2030.

“A lot of times these infections are associated with prosthetic devices like joint implants or catheters, which are common in people who are aging,” Nuxoll said. “They're going to be especially vulnerable, because their immune system becomes weaker after age 65.”

More than 2.8 million antimicrobial-resistant infections occur each year in the United States—with more than 35,000 people dying as a result.

Staph infections are notoriously difficult to treat because of antibiotic resistance and antibiotic tolerance. That’s because staph forms biofilms, a community of bacteria that adhere to each other and a surface. Internally placed medical devices, like prosthetic joints or catheters are surfaces that bacteria can adhere to and cause biofilms to form. Additionally, staph infections may keep coming back after treatment.

“It's estimated that in biofilm-mediated infections, you can have relapses occur anywhere from five to 20 percent of the time,” Nuxoll said. “You treat it with antibiotics, it looks like it goes away, and then a few months later it comes back.”

Nuxoll believes that persister cells could be to blame. Persister cells, a smaller population of bacteria in an infection, don’t respond to antibiotics—allowing some bacteria to remain in a dormant state during treatment. Once the antibiotic therapy is complete, they start to grow again.

“Once antibiotic therapy is removed, bacteria start repopulating the environment and growing again, causing relapsing infections,” Nuxoll said.

Setting a Foundation for Future Success

While the end goal is improving patient outcomes, Nuxoll and fellow researchers are currently in the stage of laying a foundation of knowledge about antibiotic tolerance.

“There isn’t a huge appreciation for antibiotic tolerance yet in the clinical setting, and we’re laying the groundwork for that.”

“We don't have answers for why a lot of antibiotic treatments fail or are ineffective,” Nuxoll said. “I have a lot of curiosity and drive in trying to get those answers and apply them to downstream applications where we can help patients.”

A variety of past and current research projects are helping Nuxoll to get there.

In 2019, Nuxoll and his collaborators published a study showing polymicrobial infections—infections caused by biofilms with more than one type of bacteria—also include an increased number of persister cells.

A follow-up study showed that persister cells can better survive the immune system as it works to fight an infection.

Nuxoll’s lab is making modifications to some antibiotics to see if they can increase their effectiveness, and in collaboration with Dr. Hector Palencia, a chemistry professor at UNK, synthesizing compounds and testing them for activity against staph in biofilm environments.

Nuxoll has also maintained a connection with his former graduate advisor, Dr. Paul Fey at UNMC, who sends clinical samples to UNK. Future work includes a partnership between Nuxoll, Fey and Dr. Kate Cooper at the University of Nebraska at Omaha to use bioinformatics and data analysis to identify differences between high and low populations of persister cells.

Extending research deeper into the medical community is part of Nuxoll’s future plans for his lab and its work.

“There isn’t a huge appreciation for antibiotic tolerance yet in the clinical setting, and we’re laying the groundwork for that,” Nuxoll said. “After initial studies are complete, we want to find a link to patient prognosis—which will require collaboration with the larger medical community.”

Developing Future Researchers Through Research

As a postdoctoral researcher, Nuxoll enjoyed research, but knew he didn't want to conduct research full time. When the opportunity for a split role as an educator and researcher became available at UNK, he knew it was a great fit.

Outside of teaching two to three undergraduate and graduate courses each semester, Nuxoll also mentors students in his lab. He currently has five undergraduate students participating in research projects. At the start, student researchers begin with hands-on training and setting experiments up under Nuxoll’s direction—but that doesn’t last long.

“It's rewarding to see experiments come together for them, because I remember the excitement I would get when they worked for me.”

“I always warn my students that I'm going to throw them into the deep end before they’re ready,” Nuxoll said. “I like for them to make mistakes, because then they are going to troubleshoot, learn from those mistakes and become independent researchers.”

His goal is to get every student to the point at which they’re setting up experiments, determining controls to include, and ultimately choosing the next steps for an experiment—or bringing new ideas to investigate. This often comes with challenges in the process, but it’s what Nuxoll finds the most meaningful—both for him and for his students. Nuxoll participated in undergraduate research himself when he was a biology student at UNK.

“Sometimes students will struggle with their research project. Experiments won’t work and they get frustrated—but something always clicks and they start to get it,” he said. “It's rewarding to see experiments come together for them, because I remember the excitement I would get when they worked for me.”

As students transition from the classroom to graduate school, clinics and labs, they’ll likely encounter some of the things they came across in Nuxoll’s lab—staph infections are present in all specialties in medicine. Outside of developing valuable critical-thinking skills, the students also build a solid foundation for their future careers in medicine:

“They make significant contributions—they're getting manuscripts by the time they graduate and presenting at national meetings,” Nuxoll said. “These aren't like your high school science projects.”