Urban Sewage in India Contains Bacteria That Survive Multiple Antibiotics

From the Editor’s Desk

March 12, 2026

Scientists studying urban sewage in India have found that wastewater flowing through city drains carries large numbers of bacteria that can survive treatment with many antibiotics. The finding suggests that sewage systems, which often flow into rivers, agricultural water, floodwater and soil, may allow these resistant bacteria to spread through the environment and eventually reach people, making some infections harder to treat.

The research, published in the journal Nature Communications, examined 381 sewage samples collected from urban areas in six Indian states. Scientists measured traces of antibiotics in wastewater, identified the bacteria living there, and analysed the genetic material those microbes carry. Their aim was to understand whether sewage systems act as reservoirs for antibiotic resistant bacteria. The results show that they do.

The researchers detected antibiotics belonging to seven different drug classes in the wastewater samples. Some medicines appeared in more than half of the samples tested. Kanamycin appeared in about two-thirds of the analysed samples, while azithromycin appeared in more than half. These drugs enter sewage mainly through human waste after people take antibiotics, through hospital discharge, and through improper disposal of medicines.

Although the concentrations were generally low, the presence of antibiotics in wastewater is worrisome because even small amounts can help resistant bacteria survive while more vulnerable bacteria die off. Gradually, this creates conditions in which resistant microbes gain an advantage.

Alongside these drug residues, scientists found an enormous variety of bacteria. Genetic analysis of the samples identified more than 2,000 distinct bacterial sequence variants in the sewage. Many of these bacteria carried resistance genes, pieces of DNA that allow bacteria to survive treatment with antibiotics.

The study identified 82 different antibiotic resistance genes in the wastewater samples. These genes allow bacteria to defend themselves against commonly used medicines such as beta lactams, macrolides and sulfonamides. Several of the resistance genes appeared in more than half the samples tested.

Even more significant was the discovery that many of these resistance genes were attached to mobile genetic elements. These are pieces of DNA that bacteria can exchange with one another. Through this process, called horizontal gene transfer, a bacterium that has learned how to survive an antibiotic can pass that ability to other bacteria living nearby.

In an environment such as sewage, where thousands of bacterial species live together, this exchange becomes easier.

To see whether these microbes could actually survive antibiotic treatment, the researchers grew hundreds of bacterial strains isolated from the sewage samples and tested them against different antibiotics. Out of 681 bacterial isolates examined, 93.8 percent showed resistance to more than 10 antibiotics.

Many of the resistant bacteria belonged to groups that doctors frequently encounter in hospital infections. These included bacteria related to Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa and Escherichia coli, microbes known to cause pneumonia, bloodstream infections and other serious illnesses.

Nearly 70 percent of bacteria belonging to the Enterobacteriaceae family, a group that includes common microbes such as E. coli and Klebsiella, were resistant to carbapenems. Carbapenems are among the most powerful antibiotics doctors use to treat severe infections, often after other medicines have failed. If bacteria become resistant to these drugs, doctors are left with very limited treatment options.

The researchers also found strains of Enterococcus faecium resistant to vancomycin, another critical antibiotic used to treat severe infections.

Scientists compared the genetic makeup of bacteria found in sewage with bacteria that have caused infections in patients. They found that several of the sewage bacteria were very similar to strains previously reported in hospitals. Some E. coliand Klebsiella bacteria from sewage were genetically close to strains doctors have seen in patients in India and other countries.

The similarity suggests that some of the bacteria found in sewage are closely related to the bacteria that infect patients in hospitals. This happens because bacteria from people’s bodies leave the body through human waste and enter the sewage system. In the wastewater, these bacteria mix with many other microbes, including those that carry resistance genes. In such crowded environments, bacteria can exchange these genes with each other, which can help more of them survive antibiotics.

The study also found differences between sewage from hospitals and sewage from general urban drains. Hospital wastewater contained higher concentrations of some medically important bacteria, reflecting the intense use of antibiotics in clinical environments.

At the same time, community sewage contained a wider diversity of microbes because it collects waste from large numbers of households.

Geography also appeared to influence the microbial landscape. Samples from Haryana showed particularly high bacterial diversity compared with other states in the study. Scientists also observed seasonal changes in microbial composition, with some bacterial species becoming more common during certain months of sampling.

These patterns suggest that antibiotic use, sanitation infrastructure, climate conditions and wastewater management practices all influence how resistance develops in the environment.

The findings are significant because sewage does not remain isolated from daily life. In many cities, wastewater flows through open drains, enters rivers after incomplete treatment, or contaminates soil and water sources used by nearby communities.

Through floodwater, irrigation, contaminated drinking water, or contact with polluted environments, resistant bacteria can return to human populations. Even if exposure does not cause immediate illness, bacteria carrying resistance genes can enter the human gut and share those genes with other microbes living in the body.

Public health researchers increasingly see wastewater surveillance as a useful early warning system for antibiotic resistance. By testing sewage regularly, scientists may detect rising resistance patterns before hospitals begin reporting large numbers of difficult infections.

Scientists say sewage can act as an early warning system. Because wastewater collects waste from entire communities, testing it can reveal which resistant bacteria are circulating among people. The purpose of such monitoring is to detect dangerous trends early, while also strengthening sewage treatment systems so that contaminated water does not return to the environment.

You have just read a News Briefing, written by Newsreel Asia’s text editor, Vishal Arora, to cut through the noise and present a single story for the day that matters to you. We encourage you to read the News Briefing each day. Our objective is to help you become not just an informed citizen, but an engaged and responsible one.