Antimicrobial resistance at the animal / environment interface: phenotypic detection and persistence of ESBL and carbapenemase producing Enterobacterales in Irish cattle systems

Antimicrobial resistance (AMR) is a critical One Health challenge at the interface of agriculture, the environment and human health. In Ireland, cattle production systems generate large volumes of manure and slurry, which are routinely applied to land. However, data on the prevalence and environmental persistence of clinically important resistance phenotypes remain limited. This study investigated the occurrence, characterisation and persistence of extended-spectrum {beta}-lactamase (ESBL) and carbapenemase-producing Enterobacterales (CPE), as well as fluoroquinolone-resistant bacteria on Irish cattle farms. A total of 450 pooled bovine faecal samples were collected from farms across 25 counties, screened using selective culture, antimicrobial susceptibility testing, and MALDI-TOF MS identification. Carbapenemase activity in presumptive CPE isolates was confirmed using phenotypic and biochemical assays, including MALDI-TOF MBT STAR analysis to demonstrate carbapenem hydrolysis. In parallel, a controlled persistence study evaluated the survival of phenotypically resistant ESBL and CPE bacteria in bovine slurry under simulated seasonal conditions. Overall, 29.6% of farms were positive for ESBL and/or CPE, with ESBL only resistance most prevalent (13.7%), followed by combined ESBL and CPE phenotypes (7.5%). Fluoroquinolone resistance was frequently detected and commonly co-occurred with {beta}-lactam resistance, indicating multidrug resistance. Escherichia coli was the dominant carrier of both ESBL and carbapenemase phenotypes. Persistence experiments demonstrated sustained phenotypic resistance in slurry for up to nine months under simulated winter conditions and up to three months during simulated summer conditions, with resistance becoming undetectable following extended verification. These findings demonstrate that clinically important AMR phenotypes are embedded within Irish cattle production systems and can persist in agricultural waste streams, highlighting slurry as a significant environmental reservoir with implications for environmental dissemination and One Health surveillance.