When many disease-causing bacteria encounter penicillin, they are not always destroyed immediately. Instead, they shift into a temporary survival state called antibiotic tolerance. This state allows them to withstand drug levels that would normally eradicate them. Though not the same as full antibiotic resistance, researchers now view tolerance as a risky precursor to it.
A groundbreaking study led by postdoctoral researcher Megan Keller and senior author Tobias Dörr, associate professor of microbiology at the College of Agriculture and Life Sciences and faculty at the Weill Institute for Cell and Molecular Biology, reveals for the first time the metabolic changes that allow bacteria to survive high doses of penicillin, a classic β-lactam antibiotic. The study also uncovered a weakness in how the bacteria survive, which may help scientists find better ways to combat antibiotic tolerance in the future.
New Insights into Bacterial Survival Mechanisms
Published in npj Antimicrobials & Resistance, the research identifies a surprising frailty of the bacteria under penicillin stress: they become starved for nucleotides. These are the basic molecular building blocks essential for many key cell processes that enable the cell to survive.
The study focuses on Vibrio cholerae, the bacterium that causes cholera, and is often used to study antibiotic tolerance. “When exposed to penicillin, the bacteria stop dividing while the drug is present,” Dörr explained. “But they stay metabolically active and survive. Once the antibiotic fades, they can return to normal growth and continue infection.”
Mapping the Bacterial Response
To understand how the bacteria survive such tough conditions, Keller and the team employed two main methods. They studied which genes turned on or off during penicillin treatment and measured the thousands of molecules the cell produced simultaneously. This approach provided the most detailed map so far of what happens inside bacteria during strong β-lactam (penicillin-type) antibiotic stress.
Many expected shifts appeared, Dörr noted. Genes involved in cell wall repair increased their activity as the bacteria attempted to rebuild the damage caused by the drug. Both purine and pyrimidine pathways, which help create nucleotides, also increased their activity.
“The most striking change our research revealed, though, was a sharp drop in nucleotides, the critical precursors for DNA and other important cell components,” Dörr said.
Exploiting Bacterial Weaknesses
This discovery led to a new question: if the bacteria are already low on nucleotides, could blocking nucleotide production even more make them easier to destroy? To test this, the team treated cholera bacteria with penicillin plus trimethoprim, which is known to interfere with nucleotide production.
The results were striking. Either drug alone eradicated only modest numbers of bacteria, but together they reduced V. cholerae survival by more than 100,000-fold. The same strong effect appeared in other medically important species, including Klebsiella pneumoniae, the cause of antibiotic-resistant pneumonia and urinary tract infections, as well as the food-borne pathogen E. coli.
By finding a metabolic bottleneck that bacteria must overcome to survive penicillin, the study points toward new treatment strategies. Instead of relying on higher antibiotic doses, which can fuel resistance and harm patients, future therapies might include compounds that exploit the nucleotide shortage caused by penicillin, Dörr said.
Implications for Future Antibiotic Strategies
It may be realistic to repurpose older drugs like trimethoprim as adjuvants to β-lactams in clinical settings, where such approaches could make existing antibiotics more effective. Combination drug “cocktails” as therapeutics are already common, Dörr noted, but have not been used specifically to target nucleotide synthesis alongside β-lactam antibiotics.
This research was funded by the National Institutes of Health and partially supported by a seed grant from the Cornell University Biotechnology Resource Center (BRC) and by the Cornell Center for Antimicrobial Resistance Research and Education (CCARRE).
As the fight against antibiotic resistance continues, studies like this one offer a beacon of hope by uncovering vulnerabilities in bacteria that can be targeted by existing and new treatments. The potential to enhance the effectiveness of current antibiotics through strategic combinations could play a crucial role in managing bacterial infections more effectively.
