Description of novel resistance islands harbouring blaCTX-M-2 in IncC type 2 plasmids

•blaCTX-M-2 was located in a complex class 1 integron In35::ISCR1::blaCTX-M-2.•In35 was inserted in two novel transposons (Tn7057 and Tn7058).•Both transposons are a hybrid of Tn1696, Tn21 and Tn1000/Tn2*.•Tn7057 and Tn7058 were located in IncC type 2 plasmids belonging to ST3.•The conjugation frequency was in the order of 10–3 for both plasmids. We sequenced two IncA/C plasmids harbouring blaCTX-M-2 in Klebsiella pneumoniae clinical isolates and compared their antibiotic resistance islands. Transconjugants were obtained from two clinical K. pneumoniae isolates harbouring blaCTX-M-2. Plasmid DNA from transconjugants underwent short-read whole-genome sequencing, reads were assembled, and gaps were closed by PCR and sequencing. Determination of plasmid replicons, antibiotic resistance genes, identification and characterisation of insertion sequence (IS) elements, and comparison with publicly available plasmid sequences were performed. blaCTX-M-2 was located in a complex class 1 integron In35::ISCR1::blaCTX-M-2, inserted in two different transposons designated Tn7057 and Tn7058, that reside in the resistance islands of plasmids pUR-KP0923 and pUR-KP1025, respectively. The general modules of both transposons were In35::ISCR1::blaCTX-M-2–Tn1000-like–Tn2*–ISKpn11-12-13 variable module–ΔTn21. In Tn7057 there was ΔIS10R–catA2 associated with an additional ISKpn13. Both plasmids belonged to IncC type 2 and ST3. pUR-KP0923 was 167 138 bp in length and had a 37 926-bp resistance island at position 4 (RI-4). Plasmid pUR-KP1025 was 168 128 bp with a RI-4 of 36 222 bp. This report describes the molecular nature of two transposons (Tn7057 and Tn7058) harbouring blaCTX-M-2 that reside in IncC type 2 ST3 plasmids. These transposons mediate resistance to oxyimino-cephalosporins, gentamicin and, in the case of Tn7057, chloramphenicol. CTX-M-2 is an important extended-spectrum β-lactamase (ESBL) to South American epidemiology. It is remarkable that despite being only two plasmid sequences, the information revealed here could contribute to a better understanding of the resistance islands from IncC type 2 plasmids.