Surveillance gap in seafood safety: Multidrug resistant Vibrio parahaemolyticus detected in shrimp imported to Norway

Abstract

Bacteria in the genus Vibrio are naturally found in marine and brackish waters and represent one of the main challenges to microbial seafood safety. However, no regulations currently address the threat posed by human pathogenic vibrios. This is of particular concern for seafood products imported from countries with high usage of antibacterial agents and frequent reporting of antibiotic resistant pathogens, including resistant vibrios. Viet Nam is one of the major providers of seafood exported to Norway, contributing with 137 tonnes of raw and frozen whiteleg shrimp (Litopenaeus vannamei) in 2021. Eight samples of whiteleg shrimp collected at Norwegian border control stations were examined for pathogenic Vibrio spp. Two of these samples tested positive for Vibrio parahaemolyticus, and the isolates were further subjected to antibiotic susceptibility testing and whole genome sequencing. The isolates, termed 556-1 and 1889-1, expressed phenotypic resistance and harboured resistance genes against clinically important antibiotics, including cephalosporins (bla_CTX-M), trimethoprim (dfrA), sulphonamides (sul2), aminoglycosides (aph(3″)-Ib, aph(6)-Id, aac(3)-Iie) and amphenicols (catC). Furthermore, phenotypic resistance to legally applied antibiotics such as oxytetracycline and oxolinic acid, as well as antibiotics banned in Vietnamese aquaculture like enrofloxacin and ciprofloxacin, was also observed. Although the isolates did not harbour any of the main known virulence genes (tdh, trh), an overlapping pool of resistance genes has emerged in V. parahaemolyticus strains isolated from both clinical, shrimp, and environmental sources. The present work provides the first documentation of V.parahaemolyticus with acquired clinically relevant antibiotic resistance entering Norway through imported seafood. These findings highlight the need for a One Health approach to combat the global spread of multidrug resistant bacteria through the international food trade, by strengthening the surveillance and regulatory framework considering pathogenic Vibrio spp. in seafood.