Antimicrobial susceptibility and distribution trends among inducible AmpC-producing Enterobacterales at a regional health authority in British Columbia: a 5-year retrospective review

Introduction. Existing literature supports using cefepime as a carbapenem-sparing agent to treat AmpC-producing Enterobacterales infections. To characterize existing susceptibility trends, we conducted a 5-year retrospective study assessing MIC distributions for ceftriaxone, cefepime, piperacillin–tazobactam and meropenem across Vancouver Island Health Authority (Vancouver Island, British Columbia, Canada).

Methods. MIC data for AmpC isolates between November 2019 and October 2024 were retrieved (BD EpiCenter™). Blood cultures, invasive specimens, urine and miscellaneous samples (e.g. respiratory and wounds) were included; we excluded surveillance specimens. MIC values were interpreted based upon CLSI M100-E34 breakpoints (Table 2a-1). Descriptive statistics were computed and compared between moderate-risk AmpC (MRAC) inducers versus low-risk AmpC (LRAC) inducers.

Results. A total of 5,631 isolates were analysed, with 3,778 (67.1%) identified as MRAC. Across all organisms, susceptibility rates for ceftriaxone, piperacillin–tazobactam, cefepime and meropenem were 82.0%, 87.0%, 95.4% and 98.7%, respectively. Compared to LRAC, MRAC organisms demonstrated lower susceptibility to ceftriaxone (76.0% versus 94.2%) and piperacillin–tazobactam (81.3% versus 98.6%). Cefepime and meropenem demonstrated similar susceptibility rates between LRAC and MRAC. MIC ₉₀ for cefepime was 1 µg ml ⁻¹ for all species except Enterobacter cloacae (MIC ₉₀ 4 µg ml ⁻¹ ).

Conclusion. Between 2019 and 2024, 95.4% of our isolates demonstrated susceptibility to cefepime within our local health authority. Further research will correlate patient outcomes and establish MIC thresholds to guide routine testing and clinical use of cefepime.