A recent study has found that latent antimicrobial resistance is more widespread globally than previously recognized. The research, published in Nature Communications, involved analysis of 1,240 wastewater samples from 351 cities across 111 countries. The project was coordinated by the DTU National Food Institute in Denmark.
The study focused on latent antimicrobial resistance genes, which do not currently pose a major risk but could become problematic in the future. Researchers recommend increasing surveillance of these genes in wastewater to better understand and manage potential risks. The findings were published in Nature Communications (https://doi.org/10.1038/s41467-025-66070-7).
"The research shows that we have a latent reservoir of antimicrobial resistance that is far more widespread around the world than we had expected," said researcher Hannah-Marie Martiny, who co-authored the study with Associate Professor Patrick Munk.
Researchers compared both latent and acquired (active) antimicrobial resistance genes and discovered that latent genes are distributed much more widely geographically than acquired ones. Consistent with previous studies, higher amounts of acquired resistance genes were found in sub-Saharan Africa, South Asia, and the Middle East and North Africa regions.
Bacteria naturally carry genes that can make them resistant to antibiotics. These genes are found everywhere—in soil, water, and humans. However, antibiotic use and environmental pressures have caused resistance to spread significantly worldwide. According to the World Health Organization (WHO), antimicrobial resistance is considered a pandemic (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).
Traditionally, studies focus on acquired antibiotic resistance genes because they can move between bacterial hosts and make treatment difficult or impossible for humans and animals.
"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," said Martiny.
Globally, there are more latent than acquired resistance genes; only sub-Saharan Africa has equal numbers of each type.
"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," said Martiny.
"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," added Munk.
Latent resistance gene identification involves extracting DNA from samples then testing random fragments for their ability to confer antibiotic resistance using functional metagenomics methods. This process does not necessarily mean these DNA fragments move between bacteria naturally outside laboratory conditions.
Acquired resistance genes are known for their ability to jump between bacterial hosts; latent ones have only shown this capacity under laboratory conditions so far.
"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 latent genes evolve into problematic acquired ones remains unknown. Broader monitoring could help answer this question by mapping where such changes occur geographically or environmentally.
Awareness typically arises when infectious diseases resist treatment due to these genetic changes. The DTU National Food Institute maintains an extensive collection of such gene data used globally by doctors and researchers (https://genepi.food.dtu.dk/resfinder). In this study all identified gene types were quantified across wastewater samples worldwide.
