Table 4_ISEcp1-associated dissemination of blaCTX-M/blaCMY-2 among cefotaxime-resistant non-typhoidal Salmonella from patients with diarrhea in Chongqing, China, 2022–2024.xlsx

ISEcp1 flanked bla_CTX-M/bla_CMY-2 in 94.4% (34/36) of isolates, highlighting its major role in mobilizing these resistance genes. IncHI2A was the most frequently identified plasmid (50.0%). In an S. I 4,[5],12:i:- isolate, a 96,117-bp IncI1 plasmid carrying ISEcp1-bla_CMY-2 was 100% identical to a Botswana E. coli plasmid.

In an S. Thompson isolate, a 152,834-bp IncC plasmid carrying the same transposition unit shared >99% identity with a plasmid from a Hefei clinical isolate. Notably, a novel 75,302-bp ISEcp1-mediated transposition unit carrying bla_CTX-M-65, together with the entire IncI plasmid backbone, was identified with 5-bp direct repeats. This unit is far larger than typical ISEcp1-mediated insertions (2.9–3.0 kb).</p>Conclusion<p>Our findings suggest that ISEcp1 is associated with the dissemination of bla_CTX-M/bla_CMY-2 among CTX-resistant isolates in this regional collection, and suggest the potential to mobilize large DNA segments.

Enhanced genomic surveillance of such mobile elements is urgently needed in this region.</p>