April 7, 2011 | 4
Poor sanitation can foster transmission of all sorts of nasty bacterial bugs. But a new study has found that among common bacteria, antibiotic resistance is brewing in the New Delhi water supply—and spreading in at least 20 strains, including some that cause dysentery and cholera.
Genetic adaptations that help bacteria combat pharmaceutical assaults give strains a better chance of surviving—and spreading. These genes are then able to move among different species, pushing the trait into new types of bacteria.
"Resistance of this scale could have serious public health implications because so much of modern medicine is dependent on the ability to treat infection," wrote the authors of a new study on one such drug-resistant gene.
The gene, known as NDM-1 (New Delhi metallo-beta-lactamase 1), had been found in E. coli, pneumonia-causing Klebsiella, and Citrobacter, which can cause urinary tract infections and sepsis. It allows bacteria to handily defeat a host of popular drugs—including penicillin and cephalosporin—by manufacturing an enzyme that disarms the medication. NDM-1 was first identified in an infected Swedish patient in 2008 who had undergone medical treatment in India, where antibiotics are less tightly regulated. A more recent analysis found that isolates might have been in New Delhi as early as 2006.
This drug-disabling gene had originally been associated with healthcare settings—especially those on the Indian subcontinent. But some travelers who hadn’t been admitted to hospitals during their travels returned home with E. coli that tested positive for the NDM-1 bacterial mutation, "suggesting possible transmission via the fecal-oral route," Mohd Shahid, of the Department of Medical Microbiology at the Jawaharlal Nehru Medical College and Hospital in Uttar Pradesh, India, wrote in an essay to accompany the new study, both of which were published online April 6 in The Lancet Infectious Diseases.
The new study, led by Timothy Walsh of the Brisbane Hospital in Australia, is one of the first to sample a larger community environment for signs of these genes. To assess the prevalence of NDM-1, the team collected 50 samples of tap water and 171 samples of water that had collected into standing pools or rivulets near public places in September and October 2010. The resistance gene was detected in two of the public water samples and 12 of the seepage water samples. For comparison, researchers also tested 70 samples of sewage in Cardiff Wales, where they found no trace of the gene.
The two public water supplies that tested positive for NDM-1, near the Yamuna River in the Ramesh Nager district and near the Red Fort, are places where locals obtain daily water for drinking, cooking, bathing and other household uses. And seepage samples that had the drug-resistance gene came from areas near the commercial and financial districts, as well as the Gol Market and Sir Ganga Ram Hospital and other busy public areas.
"There is an urgent need for broad epidemiological and environmental studies to be done, not just in India, but also in Pakistan and Bangladesh, which are source countries for other exported cases," Walsh and his colleagues wrote.
Finding the gene in the bacterium that causes cholera means that Vibrio cholerae might not be cleared by the antibiotics that are often administered in combination with rehydration therapy—the standard one-two punch against the disease. The researchers also isolated one strain of NDM-1-positive dysentery-causing Shigella boydii (named strain 65-5) that was resistant to all of the primary pharmaceutical treatments as well as some other first-line antibiotics. "Dysentery caused by strain 65-5 is potentially untreatable," the researchers concluded.
The researchers also found that the NDM-1 genes were much more prone to swap (by as much as 1 million times) between bacterial species at 30 degrees Celsius (86 degrees Fahrenheit) than at 25 C or 37 C (which is body temperature). This temperature happens to be within the daily reach for much of the year in New Delhi—including monsoon season, "when floods and drain overflows are most likely, which potentially disseminates resistant bacteria," the authors explained. And the fact that the gene transfer happens more easily at ambient temperatures suggests that the bacteria have found environmental mixing "more important than in the gut."
India has all of the ingredients to further the spread of these resistance genes, Patrice Nordmann, of La Kremlin-Bicetre in France, explained at the 2010 American Society for Microbiology meeting in Boston. The overuse of antibiotics, dense population and poor sanitation "may fuel these resistance bugs," he said, which can then "spread worldwide just by plane and by transfer of population." It’s been estimated that in the Indian subcontinent, where some 1.3 billion people live, about 650 million people do not have access to flushable toilets. And in New Delhi, the municipal sewage system only serves about 60 percent of residents.
So rather than a question of whether this agile antibiotic resistance gene will go global, "it’s a question of time," Nordmann noted at last year’s meeting. Cases in travelers have already been identified in the U.S., Canada, the U.K. and other countries. But the U.S. Centers for Disease Control and Prevention noted that it is "not aware" of any NDM-1-making bacteria having been found in environmental sources in the U.S., and, notes CDC spokesperson Kristen Nordlund, "there has been no transmission documented here in the States."
Nevertheless, the new findings "clearly show the grave potential for widespread dissemination of [beta-lactamase] NDM-1 in the environment," Shahid wrote.
And the fight against drug-resistant bacteria is likely to be an uphill battle. After all, as Shahid noted in his essay, we’re fighting the force of evolution itself: "The accumulation of antibiotic resistance in bacteria, is beyond any doubt, a practical demonstration of the Darwinian rule of the survival of the fittest."
Image courtesy of iStockphoto/thinqkreations
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