Not all patients infected with NDM-1-positive bacteria have a history of hospital
admission in India, and extended-spectrum β-lactamases are known to be circulating
in the Indian community. We therefore measured the prevalence of the NDM-1 gene in
drinking water and seepage samples in New Delhi.
Swabs absorbing about 100 μL of seepage water (ie, water pools in streets or rivulets)
and 15 mL samples of public tap water were collected from sites within a 12 km radius
of central New Delhi, with each site photographed and documented. Samples were transported
to the UK and tested for the presence of the NDM-1 gene, bla(NDM-1), by PCR and DNA
probing. As a control group, 100 μL sewage effluent samples were taken from the Cardiff
Wastewater Treatment Works, Tremorfa, Wales. Bacteria from all samples were recovered
and examined for bla(NDM-1) by PCR and sequencing. We identified NDM-1-positive isolates,
undertook susceptibility testing, and, where appropriate, typed the isolates. We undertook
Inc typing on bla(NDM-1)-positive plasmids. Transconjugants were created to assess
plasmid transfer frequency and its relation to temperature.
From Sept 26 to Oct 10, 2010, 171 seepage samples and 50 tap water samples from New
Delhi and 70 sewage effluent samples from Cardiff Wastewater Treatment Works were
collected. We detected bla(NDM-1) in two of 50 drinking-water samples and 51 of 171
seepage samples from New Delhi; the gene was not found in any sample from Cardiff.
Bacteria with bla(NDM-1) were grown from 12 of 171 seepage samples and two of 50 water
samples, and included 11 species in which NDM-1 has not previously been reported,
including Shigella boydii and Vibrio cholerae. Carriage by enterobacteria, aeromonads,
and V cholera was stable, generally transmissible, and associated with resistance
patterns typical for NDM-1; carriage by non-fermenters was unstable in many cases
and not associated with typical resistance. 20 strains of bacteria were found in the
samples, 12 of which carried bla(NDM-1) on plasmids, which ranged in size from 140
to 400 kb. Isolates of Aeromonas caviae and V cholerae carried bla(NDM-1) on chromosomes.
Conjugative transfer was more common at 30°C than at 25°C or 37°C.
The presence of NDM-1 β-lactamase-producing bacteria in environmental samples in New
Delhi has important implications for people living in the city who are reliant on
public water and sanitation facilities. International surveillance of resistance,
incorporating environmental sampling as well as examination of clinical isolates,
needs to be established as a priority.
Copyright © 2011 Elsevier Ltd. All rights reserved.