Co-integrate Col3m bla_NDM-1-harboring plasmids in clinical Providencia rettgeri isolates from Argentina

The first cases of bla(NDM) in Argentina were detected in three Providencia rettgeri (Pre) recovered from two hospitals in Buenos Aires city in 2013. The isolates were genetically related, but the plasmid profile was different. Here, we characterized the bla(NDM-1)-harboring plasmids of the first three cases detected in Argentina. Hybrid assembly obtained from short- and long-read sequencing rendered bla(NDM-1) in Col3M plasmids of ca. 320 kb (p15268A_320) in isolate PreM15268, 210 kb (p15758B_210) in PreM15758, and 225 kb (p15973A_225) in PreM15973. In addition, PreM15758 harbored a 98-kb circular plasmid (p15758C_98) flanked by a putative recombination site (hin-TnAs2), with 100% nucleotide ID and coverage with p15628A_320. Analysis of PFGE/S1-nuclease gel, Southern hybridization with bla(NDM-1) probe, hybrid assembly of short and long reads suggests that pM15758C_98 can integrate by homologous recombination. The three bla(NDM-1)-plasmids were non-conjugative in vitro. Moreover, tra genes were incomplete, and oriT was not found in the three bla(NDM-1)-plasmids. In two isolates, bla(NDM-1) was embedded in a partially conserved structure flanked by two ISKox2. In addition, all plasmids harbored aph(3')-Ia, aph(3')-VI, and qnrD1 genes and aac(6)Ib-cr, bla(OXA-1), catB3, and arr3 as part of a class 1 integron. Also, p15268A_320 and p15973A_225 harbored bla(PER-2). To the best of our knowledge, this is the first report of clinical P. rettgeri harboring bla(NDM-1) in an atypical genetic environment and located in unusual chimeric Col3M plasmids. The study and continuous surveillance of these pathogens are crucial to tracking the evolution of these resistant plasmids and finding solutions to tackle their dissemination. IMPORTANCE Infections caused by carbapenem hydrolyzing enzymes like NDM (New Delhi metallo-beta-lactamase) represent a serious problem worldwide because they restrict available treatment options and increase morbidity and mortality, and treatment failure prolongs hospital stays. The first three cases of NDM in Argentina were caused by genetically related P. rettgeri recovered in two hospitals. In this work, we studied the genetic structure of the plasmids encoding bla(NDM) in those index cases and revealed the enormous plasticity of these genetic elements. In particular, we found a small plasmid that was also found inserted in the larger plasmids by homologous recombination as a co-integrate element. We also found that the bla(NDM) plasmids were not able to transfer or move to other hosts, suggesting their role as reservoir elements for the acquisition of resistance genes. It is necessary to unravel the dissemination strategies and the evolution of these resistant plasmids to find solutions to tackle their spread.