Genetic characterisation of antibiotic resistance transposons Tn6608 and Tn6609 isolated from clinical Pseudomonas strains in Cyprus

•Nested resistance transposons were identified in clinical isolates of Pseudomonas spp.•Tn6608 and Tn6609 are built on a base element of an ancestral Tn1403 transposon (Tn1403A).•Tn6608 and Tn6609 contain different structural components built on Tn1403A.•Related transposons are located in the same site in a genomic island of Pseudomonas aeruginosa. Objectives: Antibiotic therapy for Pseudomonas infections is becoming increasingly difficult. In this study, the transposons from two multidrug-resistant (MDR) clinical Pseudomonas strains containing related transposons responsible for giving rise to resistance determinants were characterised. Methods: Two MDR clinical Pseudomonas isolates were obtained from a medical facility in Cyprus. The strains were identified as Pseudomonas putida C54 and Pseudomonas aeruginosa C69. DNA was extracted from both strains and was sequenced. Transposons were identified, annotated and compared with DNA sequences in GenBank. Results: Two related nested transposons, here named Tn6608 (from P. putida C54) and Tn6609 (from P. aeruginosa C69), were characterised. The transposons are built on an ancestral Tn1403 base element (here named Tn1403A) that contains only the transposition module (tnpA and tnpR) and the associated cargo gene module (orfA, orfB, orfC and orfD) flanked by a 38-bp inverted repeat. The nested transposons identified in this study have evolved via acquisition of multiple transposons, adding multiple resistance genes to an ancestral transposon that originally lacked any resistance determinants. Conclusion: Transposons related to Tn6608 and Tn6609 have evolved and are globally disseminated. Of particular interest is that most of these nested transposons are located within the same site in a genomic island, providing alternative avenues for dissemination.