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

Abstract

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. MIC₉₀ for cefepime was 1 µg ml^-1 for all species except Enterobacter cloacae (MIC₉₀ 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.