Published online 7 April 2011 | Nature | doi:10.1038/news.2011.218

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Antibiotic resistance shows up in India's drinking water

Discovery of NDM-1 outside hospital environment raises alarm.

waterAntibiotic resistance genes have been found in bacteria in drinking water and sewage, far the hospitals the usually haunt.Gurinder Osan / AP Photo

Bacteria carrying a gene that confers resistance to a major class of antibiotics have shown up in samples of drinking water and sewage seepage from New Delhi, researchers report in The Lancet Infectious Diseases today1. This raises the danger that people will be exposed to disease-causing bacteria that cannot be treated by antibiotics.

The resistance is bestowed by a gene, blaNDM-1, that encodes the enzyme New Delhi metallo-β-lactamase 1 (NDM-1). These genes can be passed easily between bacteria by discrete rings of DNA called plasmids. The enzyme blocks the activity of a range of antibiotics including the carbapenems — drugs of last resort for resistant infections — which might be used to treat, for example, urinary-tract infections triggered by the bacterium Escherichia coli or lung infections resulting from Klebsiella pneumoniae. NDM-1-positive strains of both species have previously been found in hospitals in India and Pakistan.

NDM-1-positive bacteria have already turned up in the United Kingdom and elsewhere in patients, some of whom had previously been in hospitals in India and Pakistan2, but this is the first report to find NDM-1 in environmental samples unconnected to hospitals or infected patients.

Last year, Timothy Walsh at Cardiff University, UK, and his colleagues pinpointed the origins of the first NDM-1-positive strain to appear in the United Kingdom. Today's paper details their examination of environments outside hospital settings, intended to provide a feel for the spread of this resistance gene across New Delhi, a city with 21 million inhabitants. The researchers asked a Channel 4 reporter and his colleagues to collect samples of tap water from homes, and human waste seeping from New Delhi's sewage systems.

Spreading out

Of 50 tap-water samples, two tested positive for NDM-1, as did 51 of the 171 sewage seepage samples. In a subset of those samples, the researchers found 11 bacterial species harbouring blaNDM-1 that had not previously been known to carry it — adding to the known resistant strains of E. coli and Klebsiella.

One of the strains is a Shigella bacterium, which causes dysentery, particularly in children in developing countries. "The isolate we found and analysed is resistant to all antibiotics" that might treat it, says Walsh.

"Our data would suggest that possibly about 10% of the people in New Delhi carry NDM-1 in normal flora" in their guts, Walsh continues. If those native gut flora end up passing on resistance to harmful strains of E. coli, for example, that could lead to infections, such as cystitis, with "virtually no drugs that can treat it," he says.

Monsoon movement

The team's lab experiments show that the transfer rate of NDM-1-positive plasmids between microorganisms is most efficient at 30ºC, which, in real-world settings, might correspond to the monsoon season – when heavy rains could cause seepage pools to spread, increasing city residents' possibility of exposure to any pathogenic microbes that pick up the antibiotic-resistance gene.

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The discovery of the gene and NDM-1-carriers in tap and waste waters is not a surprise, considering previous detections reported for hospital waste water, comments Ashok Tamhankar, the national coordinator for the Indian Initiative for Management of Antibiotic Resistance. "But to what extent this situation is going to cause damage is not yet clearly scientifically established," he adds. He also suggests that city dwellers may have already developed immunity to the organisms carrying NDM-1.

In a televised news conference from New Delhi today, Vishvamohan Katoch, secretary for the department of health research, refuted the findings. "The Lancet study is unsupported by any clinical or epidemiological evidence and does not highlight the unstable character of the isolates," he said.

Walsh and colleagues' report coincides with the World Health Day focused on antibiotic resistance and how to prevent its spread spearheaded by the World Health Organization (WHO). The last WHO report on the issue, in 2000, encouraged national surveillance, transparency and international collaboration, although some critics say not much movement has been made globally.

"We are keen to work with the WHO centre in India to look at carriage of this in India," Walsh says. "In terms of resistance, the part of the iceberg that's important is what we don't see in hospitals — and, in India, that part is absolutely massive." 

Additional reporting by KS Jayaraman

  • References

    1. Walsh T. R., Weeks, J., Livermore, D. M. & Toleman, M. A. Lancet Infect. Dis. doi:10.1016/S1473-3099(11)70059-7 (2011).
    2. Kumarasamy K. K. et al. Lancet Infect. Dis. 10, 597-602 (2010). | Article | PubMed | ChemPort |
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