Laboratory tests for antibiotic effectiveness may miss a key factor: the nutrient conditions bacteria encounter during real infections.
A study at this year’s ASM Microbe conference in Washington, D.C., showed that E. coli reacts differently to antibiotics when starved for carbon, nitrogen, or both. These reactions often differ from what standard lab tests predict.
Nutrient conditions alter antibiotic results
Standard antimicrobial susceptibility testing uses nutrient-rich media. Rachana Rao Battaje, a postdoctoral fellow at Rutgers University, said those conditions do not match the environments bacteria face in the body.
“If we only look at nutrient-rich media, we miss an important part of the picture,” she said. “This may explain why some laboratory results do not match clinical outcomes.”
The research examined how E. coli responded to different antibiotics under carbon limitation, nitrogen limitation, and combined carbon-nitrogen co-limitation. Results varied by antibiotic class.
Under nitrogen-limited conditions, bacteria became more vulnerable to aminoglycosides. Carbon limitation, however, made them more resistant to ciprofloxacin. Rao Battaje noted that nitrogen limitation and aminoglycosides both disrupt protein synthesis, increasing the effect. Carbon limitation slows bacterial growth and DNA replication, which reduces ciprofloxacin’s ability to target cells.
Antibiotics can increase bacterial growth
An unexpected result emerged: under certain carbon-limited and co-limited conditions, some antibiotics did not just fail to kill bacteria—they actually increased bacterial biomass.
Related: Sports supplements for men!
“Under specific nutrient-limited conditions, including co-limitation, antibiotics are not just ineffective but seem to promote growth,” Rao Battaje said. “This indicates a compensatory response, where the cell reallocates resources to handle one stress, improving its ability to manage another.”
This challenges the idea that nutrient-poor environments always make bacteria more resistant to antibiotics. The effect depends on the type of nutrient limitation and the antibiotic’s mechanism.
Current lab tests may ignore how bacteria adapt to multiple stresses simultaneously. That oversight could explain why some antibiotics succeed in the lab but fail in patients.
Future research will examine molecular responses
Rao Battaje said upcoming work will use proteomics, transcriptomics, and metabolomics to track the metabolic pathways involved. The aim is to identify which proteins, genes, and metabolites change when bacteria face both nutrient limitation and antibiotic stress.
“We need to study what happens inside the cell,” she said. “It might involve how the cell compensates for one stress by activating certain pathways.”
These findings could improve antimicrobial susceptibility testing, bridging the gap between lab results and real-world infections.
The study, Perish or Prosper: Nutrient Limitation Drives Antibiotic Response in E. Coli, was presented at ASM Microbe 2026 in early June. Understanding these responses may help refine treatments for persistent bacterial infections.