ISEcp1-associated dissemination of bla _CTX-M/bla _CMY-2 among cefotaxime-resistant non-typhoidal Salmonella from patients with diarrhea in Chongqing, China, 2022-2024.

Authors

Na Zhao, Gang Duan, Yu Liu, Chunyan Liao, Ling Wang, Yu Zhao, Yanbin Zhou, Fei Chen, Caiyun Li, Tingyan Sun, Yong Zhu, Mansha Yuan, Linghan Kong

Published in

Frontiers in cellular and infection microbiology. Volume 16. Pages 1891482. Epub Sep 28, 2026.

Abstract

CTX-resistant Salmonella infections threaten public health. This study aimed to characterize the genetic environments of bla _CTX-M/bla _CMY-2 in CTX-resistant non-typhoidal Salmonella from patients with diarrhea in Chongqing, China (2022-2024).
Among 306 Salmonella isolates recovered from seven hospitals, 36 (11.8%) were confirmed as CTX-resistant. Antimicrobial susceptibility testing, whole-genome sequencing (WGS), genetic structure analysis, conjugation experiments, and core-genome single nucleotide polymorphism (cgSNP) analysis were performed.
All 36 CTX-resistant isolates were resistant to CTX and ampicillin; resistance rates to chloramphenicol (88.9%), tetracycline (86.1%), and ceftazidime (63.9%) were high. Thirteen serotypes were identified, with S. I 4,[5],12:i:- (30.6%), S. Goldcoast (16.7%), and S. Typhimurium (11.1%) being the most frequently identified. The most frequently detected ESBL genes were bla _CTX-M-65 (17/36) and bla _CTX-M-55 (11/36). bla _CMY-2 occurred in five isolates. QnrS co-carriage was 72.2% (26/36). 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).
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.

PMID:
42865453
Bibliographic data and abstract were imported from PubMed on 13 Oct 2026.

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