Potential intrahospital dissemination of Pseudomonas aeruginosa carrying the blaIMP-1 gene within a Tn7-like transposon

We aimed to determine the molecular characteristics of carbapenem-resistant Pseudomonas aeruginosa 18081308 and 18083286 isolated from the urine and sputum of two Chinese patients respectively, and analyzed the formation mechanism of the genetic environment in which it carries blaIMP-1. Bacterial genome sequencing was carried out on strains 18081308 and 18083286 to obtain their whole genome sequence. Average nucleotide identity (ANI) was used for their precise species identification. Serotyping and multilocus sequence typing were performed. Furthermore, the acquired resistance genes, and virulence factors of these strains were identified. The carbapenem-resistant P. aeruginosa strains isolated in the present study were of sequence type ST865 and serotype O6. They all carried the same virulence factors (PLC, ExoSTY) and resistance genes (aacC2, tmrB, and blaIMP-1). Tn6411, a Tn7-like transposon carrying blaIMP-1, was found in both strains. Detailed genetic dissection was applied to this transposon to display the genetic environment of blaIMP-1. The aacC2-tmrB region remnant-Tn6411 backbone was the original structure of this type of transposon. A Tn402-like type 1 integron (intl1-aac(6)-II-blaIMP-1) was inserted into it and formed a stable structure, which was localized in the chromosome by TnsD for transmission within P. aeruginosa; the original structure of Tn7-like transposon was localized on the plasmid by TnsE for horizontal transmission between bacterial species. The intrahospital dissemination of P. aeruginosa ST865 isolated in this study was episodic. The blaIMP-1-carrying Tn7-like transposon might enhance their ability to survive under drug selection pressure and aggravate the difficulty in treating infections.