Sewage treatment plants can turn E Coli into superbug

Sewage treatment plants which are supposed to help cities manage waste water might be serving a very different and perhaps even a dangerous purpose. They might be inadvertently making disease causing micro organisms resistant to antibiotic drugs, which are used all around the world for their containment, creating a possible public health scare.

“We found that pollution, whether in a lake or at a point of sewage discharge into a river, induced multi-drug anti-microbial resistance in collected samples of E Coli bacteria possibly transforming it into what is known as a superbug,” Manish Kumar, assistant professor of Earth Sciences at the Indian Institute of Technology, Gandhinagar told Down to Earth, on the sidelines of a conclave on sanitation organised by Delhi-based non-profit Centre for Science and Environment (CSE). Though most strains of E Coli do not cause any diseases, some of them can cause severe diarrhoea, pneumonia, urinary tract infection (UTI), cholecystitis and neo-natal meningitis.

Kumar is the lead principal investigator of a project aimed to develop new water supplies in Ahmedabad, Guwahati and Colombo which would be adapted against the challenges posed by climate change and rapid urbanisation.

The Asia Pacific Network for Global Change Research, which is funding the project, required the involvement of institutions from one developed country and two developing countries. So, University of Kanazawa and University of Tokyo from Japan, University of Ruhuna from Sri Lanka and IIT-Gandhinagar from India were roped in.

As part of the project, Kumar and his team collected water samples from lakes Kankaria and Chandola, the Sabarmati river and three effluent treatment plants (both in flow and outflow) in Ahmedabad. They then tested these samples with six different kinds of antibiotics like ciprofloxacin, norfloxacin, tetracyclin and kanamycin for antibiotic resistance.

In Sabarmati, they collected samples from three different locations — Nehru Bridge (upstream), Sardar Bridge (middle) and Fatehwadi (downstream). While the sample from Nehru Bridge showed the E Coli was not resistant to any antibiotics. But in the Sardar Bridge sample, 60 per cent of the E Coli was resistant to kanamycin and 40 per cent of the bacteria was resistant to other five drugs. But the resistance again decreased to zero further downstream in Fatehwadi showing that the river had a natural way of dealing with the phenomenon if not polluted again. But what caused the resistance to go up at Sadar Bridge?

“Sabarmati does not have a high natural flow during summers but the riverfront needs water at all times. So, the water is stored at Sardar bridge and remains stagnant. This stagnant water probably makes the E Coli antibiotic resistant,” explains Kumar.

Similarly, in the samples collected from Chandola lake, 80 per cent of the bacteria were multi-drug resistant.

The most surprising results came from the treatment plants.

“In all three treatment plants from where samples were collected and tested, the resistance was higher in the effluents than in the influents,” says Kumar.

On the other hand, the density of E Coli had decreased after treatment. This means that though the treatment had killed the bacteria, the ones that did get saved had evolved to higher antibiotic resistance.

One possible reason for this could be genetic mutation due to ultra-violet radiation treatment or even chlorination. “Since E Coli multiplies really quickly, creating new generations in 15-60 minutes, the gene transfer from one generation to the next will happen rapidly which could explain the escalation of resistance and also its quick downfall,” says Kumar.

Another scientist points out a bigger danger. “What would be even more dangerous is a horizontal gene transfer from E Coli to an entirely new species which could perhaps be more pathological. This happens,” says Sudipta Sarkar, from IIT-Roorkee, who has worked on antibiotic resistance in treated waste water in Haridwar.

One simple way out of this conundrum is to let the river come back to its natural flow. “The river has an innate capacity to decrease the anti-microbial drug resistance of E Coli through some natural processes as was seen in Sabarmati and also in Brahmaputra,” concludes Kumar.

But no natural processes exist to do this job when effluents are coming from the treatment plants and polluted lakes.

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