Most of the seafood we eat in the United States, especially shrimp, is imported. Now, new research suggests that imported seafood may be carrying more than just protein. It could also be a vehicle for the spread of antibiotic resistance.
In a study presented at ASM Microbe 2025, scientists from the University of Georgia found colistin resistance genes in bacteria isolated from imported shrimp and scallops purchased at markets in Atlanta, Georgia. Colistin is considered a last-resort antibiotic used to treat life-threatening infections. Resistance to it is rare — but rising — and poses a serious global health threat.
“We love our seafood,” said microbiologist Issmat Kassem, Ph.D., who led the study. “The bacteria that were carrying colistin resistance genes are not normally screened.”
The bacteria identified in the seafood samples carried colistin resistance genes on plasmids, circular bits of genetic material that allow resistance to spread laterally between bacteria. That means resistance isn’t just inherited. It can jump from one bacterial strain to another, even across species.
The resistance gene, known as mcr, was first identified in 2016. Since then, researchers have found at least 10 versions. Kassem and his team had previously found mcr genes in Georgia wastewater. The same bacterial host, plasmid type and gene were now identified in imported seafood.
“The good news is that we didn’t find it in locally produced seafood,” Kassem noted.
Antimicrobial resistance is a growing public health concern, responsible for hundreds of thousands of deaths globally each year. Colistin was pulled from U.S. use in the 1980s due to its toxicity but was later reintroduced because of its effectiveness against resistant infections. In some countries, however, colistin is still used in agriculture to promote animal growth, creating additional pressure for resistance to emerge.
“We live in a very connected world,” Kassem said, emphasizing the need for better monitoring of food imports and international cooperation. “We move a lot, we travel a lot, our food travels, and we are going to spread whatever emerges, even across national borders.”
The findings will be published in the journal mSphere. Funding sources for the study were not disclosed at time of publication.