目的 探讨90 d内小婴儿大肠埃希菌的耐药特点及其与日龄、感染部位及分离时间的关系。 方法 回顾性收集2020年6月—2023年12月首都医科大学附属首都儿童医学中心新生儿病房日龄在90 d内的住院患儿分离培养获得的大肠埃希菌菌株，进行药敏试验。收集日龄、感染部位、分离时间等信息，从不同角度描述大肠埃希菌的耐药特点。 结果 共纳入384例患儿，其中新生儿组（发病日龄≤28 d）253例（65.9%），小婴儿组（发病日龄29~90 d）131例（34.1%）。大肠埃希菌总体耐药率为72.4%，多重耐药率为21.0%。新生儿组更易发生侵袭性感染，而小婴儿组耐药率更高，两组多种药物耐药率差异有统计学意义（P<0.05）。肠道内菌株对β‑内酰胺类、四环素类、喹诺酮类等多类药物耐药率高于平均水平，而对磺胺类药物的耐药率较低；血液分离株对β‑内酰胺类的耐药率较高。喹诺酮类、四环素类等抗菌药物的耐药率随时间呈上升趋势，且72.9%的多部位感染患儿存在药敏模式一致的菌株，提示菌株同源。 结论 小婴儿组大肠埃希菌耐药率较高；在90 d内小婴儿中，不同日龄和感染部位的大肠埃希菌耐药情况不同，应根据日龄和感染部位科学选择抗菌药物。

Objective To investigate the antimicrobial resistance patterns of Escherichia coli isolates from infants younger than 90 days and analyze their relationships with age, infection site, and isolation time. Methods A retrospective study was performed by collecting Escherichia coli strains isolated from hospitalized infants aged ≤90 days in the neonatal ward of Capital Center for Children's Health, Capital Medical University from June 2020 to December 2023. Antimicrobial susceptibility testing was conducted. Relevant clinical information including age, infection site, and isolation time was collected to characterize the antimicrobial resistance of Escherichia coli from multiple perspectives. Results A total of 384 infants were included, among whom 253(65.9%) were in the neonatal group (age ≤28 days) and 131(34.1%) in the young infant group (29-90 days). The overall resistance rate of Escherichia coli was 72.4%, with a multidrug resistance rate of 21.0%. The neonatal group was more susceptible to invasive infections, whereas the young infant group exhibited higher antimicrobial resistance rates, with statistically significant differences observed in resistance rates to multiple antibiotics (P<0.05). Intestinal isolates showed higher resistance rates to β‑lactams, tetracyclines, and quinolones compared to the overall average, but lower resistance to sulfonamides. Blood isolates demonstrated higher resistance to β‑lactams. An increasing trend was observed in resistance to quinolones and tetracyclines over time. Among infants with multi-site infections, 72.9% had isolates with consistent antimicrobial susceptibility patterns, indicating clonal homology. Conclusions Escherichia coli isolates from infants aged 29-90 days exhibit relatively high antimicrobial resistance rates. In infants younger than 90 days, resistance patterns differ by age group and infection site, highlighting the need for rational antibiotic selection based on these factors.