Bacterial Antimicrobial Resistance Associated With Siluriformes Fish - A NARMS Study

Bacterial Antimicrobial Resistance Associated With Siluriformes Fish - A NARMS Study

Uday Dessai¹, Yesutor K. Soku², Abdelrahman Mohamed², Gamola Fortenberry¹, Catherine Rockwell¹, Jovita Haro¹, Bonnie Kissler¹ and Sheryl Shaw¹

¹USDA Food Safety and Inspection Service

²College of Veterinary Medicine, Tuskegee University

The National Antimicrobial Resistance Monitoring System (NARMS) is a surveillance program run by agency partners from the U.S. Department of Health and Human Services (HHS) and the U.S. Department of Agriculture (USDA). NARMS provides information on the emergence and trends in bacterial antimicrobial resistance (AMR), associated with major species of food-producing animals, foods and people. The Food Safety and Inspection Service (FSIS) is a USDA agency that actively participates in the NARMS surveillance program.

In late 2015, FSIS initiated exploratory Salmonella sampling in Siluriformes (an order of fish including catfish) and products derived from these fish (80 FR 75590). In 2020, under the One Health expansion, the FSIS NARMS team expanded sampling to other species of food-producing animals to study associated bacterial AMR (NARMS Expansion, FSIS Sampling Notice). As part of the NARMS expansion, FSIS added AMR testing for E. coli and Enterococcus to the ongoing Salmonella sampling. This testing was important since antimicrobials may be used in pond-raised fish, while wild-caught fish may be exposed to antimicrobial drug residues and AMR bacteria through human waste or agricultural runoff into natural bodies of water.

The Siluriformes fish (2020-2022) study results showed that of the 264 samples analyzed for Salmonella, only 44 were positive. A majority (91%) of Salmonella retrieved from Siluriformes fish were pansusceptible, i.e., not resistant to the antibiotics tested under NARMS, and multidrug resistance (MDR), defined as resistance to three or more classes of antimicrobials, was absent in these Salmonella. The predominant Salmonella serotypes in Siluriformes fish were Newport and Typhimurium. Siluriformes testing for AMR in indicator bacteria (E. coli and Enterococcus) was performed. Of the 360 E. coli isolates (from 652 samples tested) and 423 Enterococcus isolates (from 487 samples tested), 61% of E. coli and 64% of Enterococcus showed no resistance to the antibiotics tested under NARMS, and only 3% exhibited MDR. Among the AMR isolates, 28% of E. coli isolates were exclusively resistant to ciprofloxacin and one additional class of antimicrobials, and 26% of Enterococcus isolates were exclusively resistant to tetracycline and one additional class of antimicrobials. The majority (92%) of the Siluriformes associated Enterococcus isolates in this study were E. faecalis.

Under the term Siluriformes, whether pond raised, channel fish or wild caught, a variety of fish types are included. Additionally, rearing and husbandry practices and use of antimicrobials can vary. For instance, in wild caught catfish, although antimicrobials may not be used, antimicrobial drug residues may occur through human waste or agricultural runoff, and the fish raised in controlled pond environment may not have any antibiotic residues due to the adoption of prudent/judicious use of antimicrobials. These factors can greatly influence the associated bacteria and the AMR they carry. To understand the differences in AMR between the pond raised channel fish (Alabama) and FSIS' nationwide Siluriformes findings, Soku et al. (2024) conducted a hybrid study. Their findings showed that AMR in E. coli from the pond raised channel fish differed significantly from that of FSIS' nationwide Siluriformes findings.

While the low levels of AMR bacteria associated with FSIS' Siluriformes fish sampling is encouraging, the differences reported by Soku et al. (2024) are noteworthy. Although FSIS discontinued Salmonella isolation and AMR testing in Siluriformes fish, the NARMS team at FSIS intends to periodically monitor ciprofloxacin and tetracycline resistance in, E. coli and Enterococcus, respectively. Additionally, to ensure that Siluriformes fish are free of antibiotic residues, FSIS continues its routine testing and monitoring for selected antimicrobial residues.

The presence of bacteria with or without AMR in animal-derived raw food products does not imply an immediate or direct risk to consumers. There are many opportunities to reduce and kill bacteria before such products are consumed. FSIS continues to ensure food safety and safeguards public health through its stringent oversight of inspection procedures related to animal slaughter and processing, including compliance with the sanitary dressing procedures. For additional information on NARMS, readers can visit NARMS agency websites: FDA NARMS, CDC NARMS and FSIS NARMS.