Urban sewage flowing through Indian cities is rapidly becoming a breeding ground for dangerous drug-resistant bacteria, raising serious public health concerns, according to a new study published in the journal Nature. Scientists warn that untreated wastewater carrying antibiotic residues is enabling pathogens to develop resistance to commonly used medicines, pushing antimicrobial resistance beyond hospitals and into rivers and communities.
The study finds that sewage systems are acting as training grounds for bacteria, where traces of antibiotics allow microbes to adapt, survive and share resistance genes. This process, researchers say, threatens the effectiveness of widely prescribed drugs such as azithromycin and amoxicillin, which are crucial for treating everyday infections.
Hospital Pathogens Now Circulating in Sewage and Rivers
Researchers discovered that urban sewage contains bacteria genetically similar to pathogens responsible for hospital-acquired infections. Antibiotic residues entering sewage from hospitals, households, pharmaceutical use and agriculture are accelerating resistance development.
The Yamuna River, the study notes, is receiving antibiotic-contaminated wastewater from nearby urban centres, including untreated hospital effluents. Open drains, peri-urban sewage channels and poorly regulated waste disposal systems allow contaminated water to flow directly into rivers, exposing downstream communities to health risks.
Some antibiotics were detected at concentrations high enough to promote gene exchange among bacteria, enabling them to pass resistance traits across species.
Resistance Levels Higher in Sewage Than Hospitals
Antibiotic resistance genes, or ARGs, were found to be more prevalent in sewage than in hospital samples. These genes help bacteria neutralise drugs, expel them from cells or tolerate their effects, making infections harder to treat.
The study found resistance genes linked to commonly used drug classes such as beta-lactams and aminoglycosides. Alarmingly, aminoglycoside resistance genes were about 50 per cent more common in sewage than in hospital environments, indicating that resistance is spreading widely outside clinical settings.
Researchers attribute this to multiple sources, including human waste, poultry farming, fisheries and agricultural runoff, all of which contribute antibiotic residues to wastewater systems.
Genetic Match With Global Hospital Infections
To understand how resistance spreads within cities, scientists repeatedly sampled sewage from five community sites and two hospitals in Faridabad. Genetic analysis revealed that bacteria in the city’s sewage shared identical sequence types with pathogens causing hospital infections worldwide between 2019 and 2023.
These included strains of Escherichia coli, Klebsiella pneumoniae and Acinetobacter baumannii, bacteria known for causing severe infections and showing high levels of drug resistance.
The findings indicate that sewage is not just collecting waste but actively circulating clinically dangerous bacteria within urban environments.
Antibiotic Residues Found Across Multiple States
The research team analysed hundreds of sewage samples collected from six Indian states between June and December 2023. They detected residues of 11 widely used antibiotics across seven drug classes in both community sewage and hospital wastewater.
Kanamycin residues were present in 67 per cent of samples, while azithromycin was detected in 56 per cent, highlighting widespread use and environmental release. Resistance genes capable of neutralising or expelling azithromycin were common, particularly in hospital-associated wastewater.
In total, researchers identified 170 resistance genes linked to 16 antibiotic classes, underscoring the scale of antimicrobial resistance developing in urban sewage systems.
Nearly All Bacteria Showed Multi-Drug Resistance
Using advanced detection methods, including metagenomic sequencing and laboratory culturing, scientists isolated 964 bacterial samples. Of the 681 tested against 32 antibiotics, nearly 94 per cent were resistant to more than 10 drugs.
Genome sequencing further revealed resistance genes across 31 bacterial species, including E coli, K pneumoniae, Morganella morganii and Enterococcus faecium all associated with serious human infections.
“Sewage serves as a reservoir for the emergence and dissemination of extensively drug-resistant pathogens,” said Bhabatosh Das, senior author of the study, noting a direct link between antibiotic concentrations in sewage and resistant bacteria levels.
Call for Stronger Regulation and Environmental Surveillance
Experts say the findings strengthen the case for environmental surveillance of antimicrobial resistance, particularly in countries like India where antibiotic use regulation and sewage treatment remain weak.
Researchers also called for the development of an India-specific antibiotic resistance gene database, arguing that local microbial ecosystems and resistance pathways require tailored monitoring to effectively track and manage the growing threat.
Without urgent action to regulate antibiotic use and improve sewage treatment, scientists warn that urban wastewater could accelerate the spread of drug-resistant infections, undermining modern medicine’s ability to treat even common diseases.