Scientists from the University of Georgia, led by Dr. Issmat Kassem, have reported the first occurrence of colistin-resistance genes in bacteria found in imported shrimp and scallops sold in seafood markets in Atlanta, Georgia. Colistin is a last-resort antibiotic reserved for life-threatening bacterial infections that do not respond to conventional treatment.

The discovery highlights a potential route for the spread of antimicrobial resistance (AMR) genes through global seafood trade. Colistin-resistance genes can transfer between bacteria via plasmids, clearing a pathway for the emergence of deadly, untreatable bacterial infections. An accompanying article on the findings will be published in the ASM journal mSphere.

Dr. Kassem and his team studied seafood samples purchased from eight food markets in the Atlanta area. No AMR genes were found in locally produced seafood, according to Kassem. Most seafood consumed in the U.S. is imported from many countries, including around 90 percent of shrimp. Although imported seafood is tested for microbial and other types of contamination, the types of bacteria carrying the AMR genes are not normally screened during the import process.

The World Health Organization (WHO) categorizes colistin as a critically important antibiotic and notes that the emergence of colistin-resistant infections, spurred by the spread of AMR genes, are now a major threat. WHO estimates that AMR was directly responsible for 1.27 million deaths globally in 2019 and contributed to 4.95 million deaths.

Kassem's team previously found AMR genes in wastewater samples in Georgia. The same bacterial host and plasmids the team had identified in the wastewater samples were discovered in the seafood samples in Atlanta. In other studies published since that time, researchers have discovered more AMR genes in plasmids elsewhere, indicating that colistin resistance is spreading globally.

Dr. Kassem noted that food exports and imports may become a general pathway for the spread of colistin resistance, particularly since some countries do not have strict regulations in place for the use of antibiotics in food animal production. A few countries, including China, Thailand, and Indonesia, have banned colistin as an animal feed additive, but the status of colistin use in treating bacterial infections in farmed seafood is unclear. Kassem advocates for regulations and policies to include the use of more comprehensive monitoring systems and alternative practices to contain AMR throughout the food supply.

Dr. Kassem authored a feature article for Food Safety Magazine in June 2023 on the spread of AMR in food. Read the article, "Paradise Lost: The Impact of the Emergence of Antimicrobial Resistance on Food Safety," here.