Pirzadian, J.; Zandijk, W. H. A.; Heikema, A. P.; Koene, H. H. H. T.; Goessens, W. H. F.; Vos, M. C.; Klaassen, C. H. W.; Severin, J. A.

Background: Pseudomonas aeruginosa is a bacterial pathogen responsible for severe hospital-acquired infections, and is capable of forming persistent reservoirs in hospital sink drains, creating a transmission risk. In our hospital, we have cultured not only carbapenemase-producing, Verona Integron-encoded Metallo-beta-lactamase (VIM)-positive P. aeruginosa, but also VIM-positive non-aeruginosa Pseudomonas spp., from sink drains. Previously, a blaVIM-2-containing, conjugative plasmid conferring carbapenem resistance was found in a clinical P. aeruginosa isolate in our hospital. Objective: To investigate if other Pseudomonas spp. from our hospital also carried a blaVIM-2-containing plasmid, genetically characterize these plasmids, and compare these plasmids to publicly-available plasmid sequences to identify their source. Methods: Whole-genome sequencing was used to sequence chromosomes and possible plasmids from VIM-positive non-aeruginosa Pseudomonas spp. and VIM-positive P. aeruginosa strains. Hybrid assemblies were generated to reconstruct plasmid sequences. All isolates were obtained from environmental sampling or clinical cultures during a prolonged VIM-positive P. aeruginosa outbreak in our hospital. Results: An identical blaVIM-2-containing plasmid was found in six non-aeruginosa Pseudomonas (P. carnis, P. oleovorans, and a novel species) and in three P. aeruginosa isolates. The previously-reported blaVIM-2-containing plasmid was found in three additional P. aeruginosa isolates. All P. aeruginosa belonged to high-risk clones ST111 or ST446. The two plasmids were derived from both clinical isolates and isolates from sink cultures, and were unique to our hospital when compared to other publicly-available plasmid sequences. Conclusions: During a VIM-positive P. aeruginosa outbreak in our hospital, two closely-related, blaVIM-2-containing plasmids co-occurred in multiple non-aeruginosa Pseudomonas spp. and in high-risk P. aeruginosa clones ST111 and ST446. Non-aeruginosa Pseudomonas spp. cultured from either patient or sink samples may be important sources of carbapenem resistance genes, and should not be overlooked during outbreak investigations. Moreover, plasmid analysis is essential to fully understand transmission routes in hospitals.