NDM-1 superbugs found in seepage, tap water

Published in The Hindu on April 7, 2011

Gram-negative bacterial strains with NDM-1 (New Delhi Metallo-beta-lactamase-1) gene, also called the superbug, have now been detected in drinking water and seepage water samples collected from several sites in New Delhi. Seepage samples were collected from water pools found in streets or rivulets.

The findings have been published online today (March 7) in The Lancet Infectious Diseases journal.

The NDM-1 gene enables Gram-negative bacterial strains to become resistant to carbapenem, a powerful antibiotic. Bacteria that carry the antibiotic resistant gene were found in two drinking-water samples and 51 seepage water samples.

The two drinking-water samples were collected from west of the Yamuna River in the district of Ramesh Nagar and from south of the Red Fort, respectively. The seepage samples that tested positive for the NDM-1 gene were collected close to Sir Ganga Ram Hospital, Gol Market and other sites.

No panic situation

Since none of the tap water samples had stable plasmids, “the situation has not yet [become] utterly miserable,” writes Mohd Shahid in an accompanying Comment piece in the journal. Dr. Shahid is from the Department of Medical Microbiology, Jawaharlal Nehru Medical College and Hospital, Aligarh Muslim University, U.P.

In all, the researchers had collected 50 drinking-water samples (public tap water samples) and 171 seepage samples from sites within a 12 km radius of central New Delhi.

70 sewage effluent samples from Cardiff Wastewater Treatment Works were also collected as control samples.

“Some samples contained multiple NDM-1 positive species,” the authors write. “20 NDM-1 positive strains were present in the samples, including E. coli and K. pneumonia [that causes pneumonia], …and pathogenic species Shigella boydii and V. cholera [that cause dysentery and cholera, respectively].”

NDM-1 was in the news in August last year when the same journal reported that 37 U.K. patients who had undergone elective and cosmetic surgeries in India and two neighbouring countries (Pakistan and Bangladesh) were harbouring the drug-resistant bacterial strains.

Human gut bacteria

But the latest finding clearly indicates that the drug-resistant bacterial strain carrying NDM-1 gene is no longer a hospital-born infection, but is found in the environment.

The authors of the study have found that NDM-1 gene has also spread to families of bacteria that populate the human gut and cause urinary tract infection, diahorrea, to name a few. It has also spread to pathogenic bacteria species that cause cholera and dysentery.

It is indeed really possible for the NDM-1 gene that confers antibiotic resistance to move from one species to another.

The easy spread is made possible as the NDM-1 gene is carried in the plasmids of the Gram-negative bacteria. And the plasmids can move from one bacterium to another of its kind, and even to different bacterial species.

Role of temperature

But a bigger concern is the temperature conditions under which the plasmids carrying the antibiotic resistant gene get transferred to another bacterium.

It was highest at 30 degree C. In fact, it was 1 to 10,000 times higher than at 25 degree C, and 1 to 10,00,000 times higher than at 37 degree C.

What does that mean in terms of public health? 30 degree C is the average peak temperature in New Delhi, and is also the temperature that lies within the daily range of temperature of the city for seven months of the year — from April to October.

The April to October period includes the monsoon season. And that would mean that the spread of the antibiotic resistant strains to other areas is easily facilitated by rain water carrying the seepage water.

Route of transmission

That not all patients from the U.K. or other European countries who had visited India had any hospitalisation history underlines the fact that bacteria with this resistance are present in the environment.

The authors state: “NDM-1 is widely disseminated in New Delhi and has spread into key enteric pathogens.”

Faecal-oral transmission would have been the possible route for the E. coli with the NDM-1 gene to enter the gut of these patients.

In fact, about 650 million people in India do not have access to toilets. And only about 60 per cent of New Delhi’s population is served by the sewerage system.

“The data presented by [the authors] clearly show the grave potential for widespread dissemination of NDM-1 in the environment,” writes Shahid.

“NDM-1 gene has just got into the environment but is yet to be established in tap water as the isolates from the tap water did not have stable plasmids. So there is no need to worry right now if we implement policies to control the spread,” said Dr. Shahid to this Correspondent. “The sample size is also small and only two tap water samples tested positive for NDM-1 gene.”

But it is a fact that “broad epidemiological and environmental studies are now needed in other cities in India, especially those that are adjacent to New Delhi,” Dr. Shahid writes in the Comment.