Untreated sewage driving ‘superbug’ spread in urban water

Researchers have identified a high-level presence of antibiotic resistance genes in urban surface water samples in Bangladesh and made an urgent call for immediate measures to halt the spread of the "superbugs."

“The rivers and lakes of Dhaka are surrounded by highly-populated slums in which human waste is directly released into the water. The presence of human gut bacteria links to high levels of antibiotic resistance genes, suggesting that such contamination is driving the presence of these ‘superbugs’ in surface water,” a University of Birmingham statement issued on Friday quoted the research paper’s lead author Willem van Schaik as saying.  

Superbugs are strains of bacteria, viruses, parasites and fungi that are resistant to most of the antibiotics and other medications commonly used to treat the infections they cause.

Schaik, who teaches microbiology at the University of Birmingham in UK, is member of an eight-strong research team comprising four members each from the International Centre for Diarrhoeal Disease Research, Bangladesh (icddr,b) and the Institute of Microbiology and Infection of the University of Birmingham. 

Their research findings from samples collected from 24 sites of Bangladesh’s three districts — Dhaka, Mymensingh and Shariatpur— was published in mSystems, a scientific journal of the American Society for Microbiology (ASM) on July 13 under the title "Metagenome-wide analysis of rural and urban surface waters and sediments in Bangladesh identifies human waste as a driver of antibiotic resistance."

Researchers suspect that that the release of untreated sewage is a driver for the spread of environmental antibiotic resistance genes in Bangladesh, particularly in highly urbanized settings. They, however, called for further research to quantify the drivers of antibiotic resistance in surface waters in Bangladesh.

The University of Birmingham said in the statement that the researchers studied bodies of water in urban and rural sites in three areas of Bangladesh and found more antibiotic resistant faecal coliforms in urban surface water compared to rural settings. 

“Antibiotic resistance genes were detected in all samples, but their abundance varied 1,525-fold between sites, with the highest levels of antibiotic resistance genes being present in urban surface water samples” it reads.

The abundance of antibiotic resistance genes was significantly correlated with the abundance of bacteria originating from the human gut, which suggests that the release of untreated sewage is a driver for the spread of environmental antibiotic resistance genes in Bangladesh, particularly in highly urbanized settings, added the statement.

In many cases, human waste is directly released into rivers 

Researchers say that low and mid-income countries have higher burdens of multidrug-resistant infections than high-income nations, and there is thus an urgent need to elucidate the drivers of the spread of antibiotic-resistant bacteria in LMICs. 

“Here, we study the diversity and abundance of antibiotic resistance genes in surface water and sediments from rural and urban settings in Bangladesh. We found that urban surface waters are particularly rich in antibiotic resistance genes, with a higher number of them associated with plasmids, indicating that they are more likely to spread horizontally,” they wrote.  

“The abundance of antibiotic resistance genes was strongly correlated with the abundance of bacteria that originate from the human gut, suggesting that uncontrolled release of human waste is a major driver for the spread of antibiotic resistance,” they state, suggesting that improvements in sanitation in may thus be a key intervention to reduce the dissemination of antibiotic-resistant bacteria.

They further state, “Antibiotic resistance was the highest in urban areas, which suggests that human factors contribute to the accumulation of antibiotic-resistant bacteria in the environment. This was further corroborated by the correlation between the abundance of bacteria originating from the human gut and antibiotic resistance gene abundance observed in our study.”

Rivers and lakes of Dhaka are surrounded by slums with high population densities in which 13.7% of households report that human waste is directly released into lakes, ponds, or rivers, according to the study.

“Our study thus extends on previous observations that link the introduction of human sewage into river and lake systems to high levels of antibiotic resistance genes,” it said.

The University of Birmingham press release says, the prevalence of antibiotic-resistant bacteria causing infections is increasing globally, but the clinical issues, including significant morbidity and mortality, posed by these bacteria are particularly alarming in the low and mid-income countries. 

Noting that the prevalence of multidrug-resistant E. coli among healthy humans is relatively high in Bangladesh, as it is in other low- and mid-income countries, the release says, “Dhaka, has a population of around 16 million people, with a population density that ranks among the highest of any megacity, but less than 20% of households are directly connected to sewerage infrastructure.”

Antibiotic-resistant bacteria that colonize the human gut can be passed into rivers, lakes and coastal areas through the release of untreated wastewater, the overflow of pit latrines during monsoon season or by practices such as open defecation, it adds. 

“These contaminated environments are often used for bathing, for the washing of clothes and food preparation equipment, thus increasing the risk of human gut colonization by antibiotic-resistant bacteria,” reads the University of Birmingham release. 

Willem van Schaik apart, the other members of the research team are: Ross Stuart McInnes, Siu Fung Stanley Ho, and Robert A Moran from the Institute of Microbiology and Infection at the University of Birmingham; and Md Hassan uz-Zaman, Imam Taskin Alam, Md Sirajul Islam, and John D Clemens from the Laboratory of Food Safety and One Health, Laboratory Sciences and Services Division, icddr,b.  

The University of Birmingham is ranked amongst the world’s top 100 institutions. Its work brings people from across the world to Birmingham, including researchers and teachers and more than 6,500 international students from over 150 countries. 

Headquartered in Dhaka, icddr,b is one of the world’s leading global health research institutes, with a track record of carrying out high-quality research and promoting the uptake of evidence-based interventions for over 50 years. Its initial focus was on diarrhoeal disease, but icddr,b now studies multiple infectious diseases, other threats to public health, and methods of healthcare delivery.