Genetic characterization of a Citrobacter braakii isolate possessing bla NDM-1 obtained from toilet bowl water in a tertiary healthcare-associated facility in North Macedonia

Abstract Carbapenem-resistant (CR) bacteria have emerged and been spreading beyond healthcare-associated facilities into the environment. It is recognized that toilet bowl water in patient rooms of healthcare-associated facilities can be one of internal reservoirs of CR bacteria. In accordance with this idea, toilet bowl water samples were collected from patient rooms in a tertiary healthcare-associated facility in North Macedonia, and meropenem (MEM)-resistant bacterial isolates were obtained from the toilet bowl water. In this study, because a MEM-resistant C. braakii isolate, that was one of MEM-resistant opportunistic pathogens, was obtained from the toilet water, whole-genome sequencing (WGS) of this isolate was performed to obtain genetic characteristics of the bla NDM-1 -positive C. braakii isolate. By the WGS, four contigs were constructed, the longest contig, contig 1 (5,189,681 bp), contained bla CTX-M with some additional antimicrobial-resistance genes (ARGs). Interestingly, bla NDM-1 was detected in contig 2 (177,260 bp) and contig 3 (64,168 bp). Plasmid replicon of contig 2 was IncA/C2 but plasmid replicon of contig 3 was IncN and different from one of contig 2. Genetic structures surrounding bla NDM-1 were different between these two bla NDM-1 -positive plasmids implying transfer or insertion of bla NDM-1 had occurred by IS or other mechanism. Further molecular epidemiology will be needed to explain the mechanism that allowed the C. braakii isolate to possess two structurally different bla NDM-1 plasmids.