Annals of Laboratory Medicine

Korean Society for Laboratory Medicine (대한진단검사의학회)
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Molecular and Microbiological Characteristics of Uropathogenic Escherichia coli Harboring CTX-M-55

  • Heejeong Kwon (School of Medicine, Hanyang University College of Medicine) ;
  • Jeoungyeon Kim (Division of Infectious Diseases, Department of Internal Medicine, Hanyang University Seoul Hospital) ;
  • Jinnam Kim (Division of Infectious Diseases, Department of Internal Medicine, Hanyang University Seoul Hospital) ;
  • Se Yoon Park (Division of Infectious Diseases, Department of Internal Medicine, Hanyang University Seoul Hospital) ;
  • Choseok Yoon (Division of Infectious Diseases, Department of Internal Medicine, Hanyang University Seoul Hospital) ;
  • Yangsoon Lee (Department of Laboratory Medicine, Hanyang University of College of Medicine) ;
  • Bongyoung Kim (Division of Infectious Diseases, Department of Internal Medicine, Hanyang University Seoul Hospital)
  • Received : 2025.06.02
  • Accepted : 2025.11.27
  • Published : 2026.05.01
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Abstract

The extended-spectrum β-lactamase (ESBL) CTX-M-55, a CTX-M-15 variant distinguished by an amino-acid substitution (Ala77Val), has enhanced enzymatic activity due to higher structural stability. In Korea, CTX-M-55 remains insufficiently characterized, particularly in the context of urinary tract infections (UTIs). We identified CTX-M-55 among uropathogenic Escherichia coli isolates and compared its microbiological characteristics with those of CTX-M-15. In total, 247 E. coli isolates were collected from patients with acute pyelonephritis at Hanyang University Seoul Hospital, an 860-bed tertiary-care hospital, between July 2019 and December 2021. ESBL production was confirmed using a double-disk synergy test, and minimum inhibitory concentrations (MICs) were determined. Resistance genes were detected using PCR, and CTX-M-15 sequences were analyzed. Among 38 isolates detected using PCR, eight were confirmed as CTX-M-55 using further sequence analysis. CTX-M-55 showed (P >0.05) a trend toward increased resistance to aztreonam, cefotaxime, ceftazidime, and cefepime, while showing decreased resistance to amoxicillin/clavulanate and piperacillin/tazobactam. CTX-M-55 had higher MIC50 values than CTX-M-15 for ceftazidime (>16 vs. 8 ㎍/mL), cefepime (32 vs. 1 ㎍/mL), and piperacillin/tazobactam (0.5 vs. 0.25 ㎍/mL). Virulence factors and coexisting resistance genes did not significantly differ. Our findings suggest that, given its increased resistance to ceftazidime and cefepime, CTXM-55 should be considered when treating UTIs in Korea.

Keywords

Acknowledgement

This work was supported by the National Research Foundation of Korea (NRF) funded by the Ministry of Science and ICT (grant No.: NRF-2021R1C1C1004577).

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