Prevalence, bacterial load, and genomic characterization of Vibrio parahaemolyticus in freshwater-farmed Litopenaeus vannamei from China

Shrimp was the leading food vehicle for <i>Vibrio parahaemolyticus</i> outbreaks in China, yet studies on <i>V. parahaemolyticus</i> in globally predominant farmed shrimp (<i>Litopenaeus vannamei</i>) - particularly in freshwater culture remain limited. This study aimed to investigate and evaluate the contamination of <i>V. parahaemolyticus</i> in freshwater-farmed marine shrimp (<i>L. annamei</i>) in China. The prevalence and bacterial load of <i>V. parahaemolyticus</i> in shrimps were assessed by China China National Standard GB 4789.7-2013 and isolates were obtained for genomic analysis. The prevalence of <i>V. parahaemolyticus</i> in shrimp samples was 39.1% and the bacteria load ranged from 3.6 MPN/g to 24,000 MPN/g. Analysis on isolates demonstrated that 75.8% (94/124) were assigned to 28 sequence types (STs), whereas 24.2% STs were unknown. All isolates harbored 24 antibiotic resistance genes (ARGs), of which <i>tet(34)</i>, <i>tet(35)</i>, and <i>bla</i> _CARB were harbored in all isolates. There was a significant correlation between <i>bla</i> _CARB types and STs, with isolates sharing identical STs carried the same blaCARB variant. The <i>trh</i>+ isolates (9.7%, 12/124) was simultaneously coexisted with <i>hlyB</i> and <i>hlyC</i>. All four ST79 strains harbored <i>trh</i>/<i>hlyB</i>/<i>hlyC</i> and <i>bla</i> _{CARB_46}. Our findings elucidated the contamination of <i>V. parahaemolyticus</i> in freshwater-farmed <i>L. vannamei</i>, with heavy bacteria load in Fujian province. The emergence of specific ST co-harboring critical virulence genes and ARGs indicating the necessity for targeted surveillance and specified control in aquaculture systems.