"The potential for wider international spread of plasmids encoding NDM-1 is real and should not be ignored...coordinated, concrete, and collective efforts are needed, initially to limit their widespread dissemination, and finally to combat this emerging threatening resistance problem", warns Mohd Shahid from Jawaharlal Nehru Medical College and Hospital, Uttar Pradesh, India in an accompanying Comment.
In previous reports, not all patients from Europe, North America, Asia, and Australasia infected by bacteria with NDM-1 had a history of hospital admission while in India. A few studies have reported gut colonisation with NDM-1 in travellers returning from India, suggesting transmission via the faecal-oral route through close personal contact or the ingestion of water or food contaminated with the NDM-1-positive bacteria.
In this study, Timothy Walsh from Cardiff University in the UK and colleagues, together with journalists from Channel 4 television, investigated how common NDM-1-producing bacteria are in community waste seepage (water pools in streets or rivulets) and tap water in urban New Delhi.
The researchers collected 171 swabs of seepage water and 50 public tap water samples from sites within a 12km radius of central New Delhi between September and October 2010. Samples were tested for the presence of the NDM-1 gene using polymerase chain reaction (PCR) and DNA probing. All bacteria isolated from the water samples were also tested for antibiotic susceptibility and examined for NDM-1 by PCR and sequencing. NDM-1 bacterial plasmid transfer frequency was examined at three different temperatures relevant to the Indian environment: 25°C, 30°C, and 37°C.
The NDM-1 gene was found in 2 of the 50 drinking-water samples and 51 of 171 seepage samples. Bacteria positive for NDM-1 were grown from 2 drinking-water samples and 12 seepage samples.
Importantly, the gene was found in 20 bacterial isolates comprising 14 different species, including 11 species in which NDM-1 has not been previously reported. Worryingly, the gene has spread to pathogenic species including Shigella boydii and Vibrio cholera, which cause dysentery and cholera, respectively.
Interestingly, the transfer rate (rate at which the NDM-1 gene is copied and transferred between different bacteria) was highest at 30°C - a temperature lying within the daily range of temperatures in New Delhi for 7 months of the year from April to October. "This period includes the monsoon season, when floods and drain overflows are most likely, which potentially disseminates resistant bacteria", explain the authors.
They warn: "Oral-faecal transmission of bacteria is a problem worldwide, but its potential risk varies with the standards of sanitation. In India, this transmission represents a serious problem...650 million citizens do not have access to a flush toilet and even more probably do not have access to clean water."
They conclude: "International surveillance of resistance, incorporating environmental sampling as well as examination of clinical isolates needs to be established as a priority...and cover Pakistan and Bangladesh, because these are also source countries for exported cases."
Source
The Lancet Infectious Diseases