Antibiotic resistance is often framed as a hospital problem, but a growing body of evidence shows that rivers, soils, wastewater, and other natural environments are quietly becoming major reservoirs of resistant bacteria. A new review highlights a critical obstacle standing in the way of effective global surveillance: the lack of a unified standard for interpreting antibiotic resistance data.
In a comprehensive review published in New Contaminants, researchers analyze how antimicrobial resistance, or AMR, is monitored in the environment and why inconsistent interpretation of laboratory results may be distorting our understanding of the scale of the problem. The authors argue that differences in international testing standards can lead to conflicting conclusions about whether the same bacterium is classified as resistant or susceptible.
"Antimicrobial resistance does not respect borders," said corresponding author Dr. Nyuk Ling Ma. "If we use different rules to interpret the same data, we risk underestimating or misjudging resistance trends at a global scale."
At the center of the issue is the minimum inhibitory concentration, or MIC. MIC is the lowest concentration of an antibiotic that prevents bacterial growth and is considered the gold standard for determining antibiotic resistance. However, MIC values only become meaningful when interpreted using breakpoints, which are predefined thresholds that classify bacteria as susceptible, intermediate, or resistant.
Currently, the two most influential breakpoint systems are maintained by the Clinical and Laboratory Standards Institute in the United States and the European Committee on Antimicrobial Susceptibility Testing. While both are science based and widely respected, they often differ in their breakpoint values, testing approaches, and classification rules.
"As a result, the same bacterial strain tested in two laboratories using different standards may be labeled resistant in one case and susceptible in another," explained co corresponding author Dr. Hongna Li. "This inconsistency creates serious challenges for comparing resistance data across regions and over time."
The review examines a wide range of antimicrobial resistance surveillance tools, from genetic methods that detect resistance genes to phenotypic methods that measure how bacteria actually respond to antibiotics. Genetic techniques such as PCR and metagenomic sequencing are fast and sensitive, but they cannot always predict whether bacteria will behave as resistant in real world conditions. Phenotypic methods, which directly measure bacterial growth inhibition, remain essential for accurate resistance assessment.
The authors emphasize that environmental monitoring is especially vulnerable to inconsistent standards. Antibiotics are now detected at low but biologically active concentrations in rivers, soils, and wastewater worldwide. Even trace levels can promote resistance selection, making reliable surveillance crucial for both environmental protection and public health planning.
"Environmental data are increasingly being used to inform policy decisions," said Dr. Ma. "Without harmonized breakpoints, it becomes difficult to track global trends, assess risks, or evaluate whether interventions are working."
Beyond surveillance, inconsistent resistance classification may also affect antimicrobial stewardship and risk communication. Discrepancies in resistance rates could influence decisions about antibiotic use, regulation, and investment in mitigation strategies.
The researchers call for stronger international collaboration to develop a unified and authoritative MIC breakpoint framework that can be applied consistently across clinical and environmental settings. They also highlight the need for affordable, user friendly monitoring technologies that can be deployed more widely, especially in low resource regions.
"Standardization is not just a technical issue," Dr. Li said. "It is a foundation for coordinated global action against one of the most urgent public health threats of our time."
As antibiotic resistance continues to rise worldwide, the authors argue that aligning how resistance is measured and interpreted is a critical step toward understanding, managing, and ultimately slowing its spread.
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Journal reference: Tang M, Wang Z, Zhu H, Ma NL, Yang Z, et al. 2026. Antimicrobial resistance surveillance in the natural environment: standardization of minimum inhibitory concentration breakpoint. New Contaminants 2: e003 doi: 10.48130/newcontam-0025-0023
https://www.maxapress.com/article/doi/10.48130/newcontam-0025-0023
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About the Journal:
New Contaminants (e-ISSN 3069-7603) is an open-access journal focusing on research related to emerging pollutants and their remediation.
