Li, Yu-HsunYu-HsunLiLu, Po-LiangPo-LiangLuLin, Shang-YiShang-YiLinPO-REN HSUEHKo, Wen-ChienWen-ChienKoLiu, Chun-EngChun-EngLiuTang, Hung-JenHung-JenTangWang, Fu-DerFu-DerWangChen, Yao-ShenYao-ShenChenTsao, Shih-MingShih-MingTsaoHo, Mao-WangMao-WangHoChang, Ya-TingYa-TingChang2026-04-212026-04-212026-0416841182https://scholars.lib.ntu.edu.tw/handle/123456789/737362Background: Third-generation cephalosporin-resistant Enterobacterales is a recognized global concern. This study investigated the molecular epidemiology of β-lactamase genes and antimicrobial susceptibility patterns among ceftriaxone-resistant Enterobacterales causing intra-abdominal and urinary tract infections in Taiwan between 2009 and 2019. Methods: Data from the SMART surveillance program were analyzed, including Enterobacterales isolates with ceftriaxone minimum inhibitory concentrations ≥4 μg/mL. β-lactamase genes were detected using multiplex polymerase chain reaction assays. Results: The overall ceftriaxone-resistant rate among Enterobacterales was 28.2 %, with a significant annual increase in ceftriaxone-resistant Klebsiella pneumoniae in both community- and hospital-acquired infections. Among the 2614 ceftriaxone-resistant isolates, the most common species were Escherichia coli (58.4 %), K. pneumoniae (16.3 %), and Enterobacter cloacae (9.9 %). Of all ceftriaxone-resistant isolates, 27.8 % carried only AmpC genes, 38.8 % carried only ESBL genes, and 16.2 % harbored both. High carriage rates of AmpC-encoding genes were observed in E. coli (38.9 %) and K. pneumoniae (48.9 %), with an overall prevalence of 44 %. The most common genotypes were blaCMY (41.2 %), blaDHA (31.8 %), and blaACT/blaMIR (27 %). Ceftolozane/tazobactam showed poor susceptibility against ceftriaxone-resistant isolates carrying only AmpC (20.1 %) and most ceftriaxone-resistant Enterobacterales (<55 %), except E. coli. Ertapenem demonstrated low susceptibility to K. pneumoniae, E. cloacae (both approximately 50 %), and isolates harboring only AmpC genes (57.9 %). Conclusions: A high prevalence and diversity of AmpC genes were observed in E. coli and K. pneumoniae. The limited activity of ertapenem and ceftolozane/tazobactam suggests that the molecular mechanisms underlying ceftriaxone-resistant Enterobacterales in Taiwan are complex and likely involve factors beyond AmpC and ESBL carriage.entrueAmpC β-lactamaseCeftriaxone-resistant/third-generation cephalosporins resistanceEnterobacteralesExtended-spectrum β-lactamaseSMART taiwanjournal article10.1016/j.jmii.2025.08.020409129872-s2.0-105015222003