Bacterial antimicrobial resistance in routine retail and hospital food samples in Ireland, 2024

Antimicrobial resistance (AMR) represents a critical One Health challenge, with food systems serving as transmission pathways for resistant bacteria. This study provides the first comprehensive assessment of AMR in bacteria from 71 ready-to-eat (RTE) food samples collected from retail and hospital settings in Ireland. Identification of bacterial isolates and antimicrobial susceptibility testing were carried out following established international guidelines. Isolates resistant to third-generation cephalosporins were investigated for Extended-Spectrum Beta-Lactamase (ESBL) production and characterized using Whole Genome Sequencing (WGS). A total of 160 bacterial isolates were recovered, including 106 Enterobacterales. Five isolates (4.7% of Enterobacterales) demonstrated ESBL production, all identified as Rahnella species (four R. aceris, one R. victoriana) from diverse food matrices including prepared dishes, meat products, dairy products, and hospital cook-chill meals. WGS revealed chromosomally-encoded resistance genes (blaRAHN, blaRAHN-1, blaRAHN-5, blaRAHN-6), representing the first detection of ESBL-producing environmental bacteria in Irish food products. Among Enterobacterales, 52.8% showed resistance to at least one antimicrobial, with ampicillin resistance most common (51.9%). Significantly, no multidrug-resistant (MDR) isolates were detected, and all remained susceptible to critical last-resort antimicrobials, including carbapenems. In conclusion, this study demonstrates a low prevalence of MDR in Irish RTE foods. However, the discovery of chromosomal ESBLs in environmental Rahnella species highlights an underappreciated reservoir of resistance determinants within the food chain. This underscores the importance of integrated, One Health-based surveillance to monitor AMR transmission, as food meeting standard safety criteria may still act as a vehicle for resistance genes.