The
New Delhi metallo-β-lactamase (NDM-1) increases bacterial
resistance to a broad range of antibiotics, and bacteria that produce
it can cause infections that are very difficult to treat, thus posing
great risks to human health. This paper addresses the occurrence of
NDM-1 genes through different processes in wastewater treatment plants
(WWTPs). NDM-1 genes prevailed through several treatment units (including
disinfection by chlorination) in two WWTPs in northern China. Significant
NDM-1 gene levels were present in the effluent discharged from both
WWTPs (from 1316 ± 232 to 1431 ± 247 copies/mL, representing
from 4.4 to 93.2%, respectively, of influent levels). NDM-1 genes
were present at much higher concentrations in dewatered waste sludge
that is applied to soils [(4.06 ± 0.98) × 107 to (6.21 ± 2.23) × 107 copies/g of dry weight],
raising the possibility of propagation to indigenous bacteria. This
concern was validated by a conjugation experiment with Haihe River
sediment not harboring NDM-1 genes at detectable levels, where an
NDM-1-positive Achromobacter sp. isolated from a
WWTP transferred the NDM-1 gene to an indigenous Comamonas sp. The discharge of NDM-1 genes in the effluent and dewatered waste
sludge from WWTPs (even at rates higher than influent values) underscores
the need to better understand and mitigate their proliferation and
propagation from WWTPs.
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