Background: The New Delhi metallo-β-lactamase-1 (NDM-1)-positive plasmid and its variants pose daunting threats to public health. Hospital sewage was considered as an important reservoir of antibiotic genes. Numerous and diverse taxa of multidrug-resistant (MDR) bacteria carrying NDM-1-positive plasmids have been identified during routine surveillance of hospital sewage. We herein report a carbapenem-resistant Acinetobacter towneri  strain AeBJ009 with an NDM-1-positive plasmid isolated from hospital sewage.
Materials and Methods: Bacteria were isolated from cultures of hospital sewage and identified by using the Vitek 2 compact system and 16S rRNA sequencing. The blaNDM-1  gene was amplified and confirmed by sequencing. Antimicrobial susceptibility testing was performed using AST-GN14 on the Vitek2 compact system. In addition, the blaNDM-1  gene was located by Southern blotting. Conjugation experiment and whole-genome sequencing were performed for further analysis.
Results: Strain AeBJ009 was isolated from hospital sewage and identified as A. towneri . Antimicrobial susceptibility testing revealed an MDR phenotype. Pulsed-field gel electrophoresis and Southern blotting showed that strain AeBJ009 carries three plasmids and that blaNDM-1  is located on the 47kb plasmid pNDM-AeBJ009. However, the conjugation experiment to transfer pNDM-AeBJ009 to Escherichia coli  strain J53 was unsuccessful. Whole-genome sequencing found that pNDM-AeBJ009 contains a Tn 125 element carrying blaNDM-1 . The ble  gene downstream of blaNDM-1  displayed a single-nucleotide polymorphism compared to its homologue on plasmid pM131_NDM1. BLAST analysis using the Comprehensive Antibiotic Resistance Database identified no gene polymorphisms with 100% identity to our ble  variant.
Conclusion: The A. towneri  strain AeBJ009 exhibiting an extended spectrum of antibiotic resistance was isolated from hospital sewage and may potentially exacerbate the risk of MDR bacterial infections. The prevention of nosocomial infections due to drug-resistant bacteria will require enhanced monitoring and control of MDR pathogens in environmental reservoirs.
Keywords: NDM-1, ble , Acinetobacter towneri, drug resistance