Approximately 90% of shrimp consumed in the U.S. is imported

Shrimp Imports Linked to Spread of Colistin Resistance, a Last-Resort Antibiotic

UNITED STATES
Tuesday, June 24, 2025, 00:10 (GMT + 9)

Researchers Identify Resistance Genes in Imported Shrimp and Scallops, Raising Global Public Health Concerns

LOS ANGELES – Resistance to colistin, a potent, last-resort antibiotic used only to treat dangerous, life-threatening bacterial infections in humans, is spreading worldwide, diminishing treatment options and increasing risks for patients. New research from the University of Georgia, presented this week at the ASM Microbe 2025 conference in Los Angeles, has identified a previously underestimated pathway for this spread: imported seafood.

Microbiologist Issmat Kassem, Ph.D., and his team reported the first isolation of colistin-resistance genes in bacteria found in imported shrimp and scallops, purchased from eight food markets around Atlanta, Georgia. "We love our seafood," Kassem noted, explaining that approximately 90% of shrimp consumed in the U.S. is imported. While imported seafood is screened for contaminants, the current process does not detect these antimicrobial resistance genes, which are often carried on plasmids—circular bits of genetic material that can be transmitted between bacteria.

Antimicrobial resistance is a growing public health menace, causing hundreds of thousands of deaths globally every year. Colistin, introduced in the 1950s to treat infections by Gram-negative bacteria, was discontinued in the U.S. in the 1980s due to its severe side effects (nerve and kidney damage). However, its use continued in agriculture in other countries for animal treatment and growth promotion. Its reintroduction into human medicine became necessary due to the scarcity of options to treat certain resistant bacterial infections, being classified by the World Health Organization as a high-priority, critically important antibiotic.

In 2016, researchers discovered a mobile colistin resistant gene (mcr) that could be horizontally transferred via plasmids between bacteria, a crucial finding as it was previously believed that resistance was only inherited. Since then, at least ten mcr genes and many variations have been identified. Kassem, who has researched antimicrobial resistance for two decades, suspected it might spread through the international food trade.

"Our food is sourced from different places. If you go out to lunch today, your plate might have ingredients from six, seven, eight countries. Some countries do not have strict regulations for using antibiotics in food animal production, so imported food can be a vehicle for transmission of resistance," Kassem stated.

Previous work by his group had already found mcr genes in wastewater samples in Georgia, also identifying the bacterial host carrying the plasmids. The "good news," according to Kassem, is that it was not found in locally produced seafood.

Kassem cautioned that while one source of colistin resistance was identified, others likely exist and are spreading. "We live in a very connected world... our food travels, and we are going to spread whatever emerges, even across national borders. Therefore, it's important to invest in monitoring systems, expand them, and collaborate, especially at the global level, on the issue of antimicrobial resistance."

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