Study Uncovers Reservoirs of Antimicrobial Resistance in Food Processing Environments

By Michael Gwarisa

A new study has identified food processing environments, particularly wastewater and sludge, as significant reservoirs for antimicrobial resistance (AMR) genes, including several high-risk variants that pose a threat to human health. The research, led by Thorben Reiche from the Norwegian University of Science and Technology (NTNU), highlights the potential for these facilities to contribute to the environmental spread of AMR.

The study, conducted by a team of researchers from NTNU and SINTEF Industry in Norway, alongside the University of Life Sciences in Iași, Romania, investigated the prevalence of AMR in salmon and broiler chicken processing plants. The team analyzed samples from sidestream materials such as cut-offs and skin, waste discharges including wastewater and sludge, and processing surfaces across four facilities in Norway and Romania.

A key finding was the high abundance and diversity of antimicrobial resistance genes (ARGs) detected in waste discharges. Process wastewater and sludge samples contained between 32 and 330 unique ARGs, representing the highest concentrations found in the study. Among these were numerous high-risk genes, including mecA and mecR1, which are implicated in methicillin resistance in Staphylococcus aureus (MRSA). The researchers also identified blaCTX-M-1, which encodes for extended-spectrum beta-lactamase (ESBL) enzymes and confers resistance to a broad range of penicillin and cephalosporin antibiotics. In addition, tetracycline resistance was observed through the presence of tet(M) and tet(L), while qnrS1 provided resistance to fluoroquinolone antibiotics such as ciprofloxacin. Multidrug efflux pump genes like TolC and mdtE, capable of expelling multiple, unrelated antibiotic classes from bacterial cells, were also found. The study suggests that these waste streams, when released into the environment, could act as a significant dissemination pathway for AMR.

While the study collected over 300 bacterial isolates from the Enterobacterales, Enterococcus, and Pseudomonas groups, the overall prevalence of antibiotic-resistant bacteria was found to be low. Most Enterococcus and Pseudomonas isolates were susceptible to the antibiotics tested. However, there was a notable exception with the detection of quinolone-resistant Escherichia coli (QREC) in waste discharges from two broiler processing plants. Furthermore, multidrug-resistant (MDR) E. coli were identified in one plant. Whole genome sequencing of these MDR isolates revealed that they carried multiple plasmids and mobile genetic elements containing dangerous ARGs such as sul2, ant(3”)-Ia, qnrS1, and blaCTX-M-1, indicating a high potential for these genes to spread to other bacteria.

The research also examined sidestream materials destined for reuse, such as salmon cut-offs and protein powder for animal feed. While these materials harbored fewer resistant bacteria, they were found to contain a diverse array of ARGs. Salmon cut-offs, for instance, contained 99 unique ARGs. The presence of these genes in materials intended for circular economy purposes suggests a potential route for AMR to be re-introduced into new production systems.

The authors, including Anita Nordeng Jakobsen, Gunhild Hageskal, and Mihai Mares, conclude that their findings underscore a potential One-Health risk. They emphasize that while the prevalence of resistant bacteria in these environments may currently be low, the vast reservoir of resistance genes in wastewater is a significant concern. The study advocates for maintaining high hygiene and biosecurity standards in processing plants and calls for the development of more effective wastewater treatment processes capable of eliminating ARGs before discharge. The researchers also note that given the relatively small sample size of the study, further investigations are necessary to fully assess the risk of AMR dissemination through these pathways and to inform future policies and mitigation strategies.