A recent study led by the DTU National Food Institute in Denmark has found that latent antimicrobial resistance is more widespread globally than previously recognized. The research, published in Nature Communications (https://doi.org/10.1038/s41467-025-66070-7), analyzed 1,240 wastewater samples from 351 cities across 111 countries and discovered that bacterial latent antimicrobial resistance genes are present on all continents.
Latent resistance genes do not currently pose a major risk, but researchers warn that some may become problematic in the future. They recommend increased surveillance of these genes in wastewater to better understand and manage potential threats.
Researcher Hannah-Marie Martiny explained, "The research shows that we have a latent reservoir of antimicrobial resistance that is far more widespread around the world than we had expected." She co-authored the study with Associate Professor Patrick Munk.
The study compared both latent and acquired antimicrobial resistance genes. It found that while acquired resistance genes—those already able to move between bacteria—are concentrated in sub-Saharan Africa, South Asia, and the Middle East and North Africa (MENA) regions, latent resistance genes are distributed much more widely.
According to the World Health Organization (WHO), antimicrobial resistance (AMR) has reached pandemic levels due to factors such as antibiotic use and environmental pressures (https://www.who.int/westernpacific/newsroom/commentaries/detail/the-next-pandemic-is-already-here--antimicrobial-resistance-is-upending-a-century-of-achievements-in-global-health). Typically, studies focus on acquired resistance because it makes treating infections difficult or impossible. However, this new research suggests monitoring both types of genes could provide important insights into how AMR develops and spreads.
Martiny stated, "By tracking both acquired and latent antimicrobial resistance genes, we can gain a broad overview of how they develop, change hosts and spread in our environment and thereby better target efforts against antimicrobial resistance (AMR). Wastewater is a practical and ethical way to monitor AMR because it aggregates waste from humans, animals and the immediate surroundings."
Globally, there are more latent than acquired resistance genes; only sub-Saharan Africa showed equal numbers of each type. Martiny added: "In general, I don't think we need to be too worried about most latent antimicrobial resistance genes, but I do believe that some of them will eventually cause problems, and we would like to know which ones; because with that knowledge we may be able to predict which bacteria in future can be stopped by which medicines." Patrick Munk shared this view.
Munk noted: "When new antibiotics are developed - a process that takes many years - bacteria may already have invented new 'scissors' capable of destroying them. If we can study both types of genes over time, we may be able to find out which of the latent genes become problematic resistance genes, how they arise and how they spread across geography and bacteria, and in that way lessen the burden of antimicrobial resistance."
Testing whether certain genes confer antibiotic resistance involves laboratory experiments or AI-based predictions. There is uncertainty associated with computer models. Latent resistance is identified using functional metagenomics—a method where DNA fragments from samples are inserted into harmless bacteria; those surviving indicate possible new forms of antibiotic resistance.
Acquired gene movement between bacteria is well documented outside laboratories; for latent genes this ability remains uncertain outside controlled conditions. This distinction raises concerns among researchers about their potential evolution into active threats.
"Our concern is that some latent resistance genes will become acquired resistance genes and thus become able to jump to different bacterial hosts out in the environment. Especially because the research also shows that they are present in large numbers in so many places around the world. That is why we would like to see them included in surveillance," said Munk.
The extent to which these latent forms might evolve into problematic strains remains unknown. The researchers argue broader surveillance could help answer these questions.
Traditionally society becomes aware of resistant strains through outbreaks where infections cannot be treated effectively with antibiotics. Resources such as DTU’s ResFinder database (https://genepi.food.dtu.dk/resfinder) support doctors worldwide in identifying resistant bacteria using collections built up through studies like this one.
