Sea salt associated microplastics amplify pathogenic Vibrio and impair development in brine shrimp (Artemia...

Pathogens associated with microplastics in harvested sea salt could increase infection in inland mariculture. In the present study, two separate sets of tests: an in vitro test to examine the effects of microplastics on biofilm formation by Vibrio harveyi, and an in vivo test to evaluate the development of brine shrimp (Artemia franciscana) cultured using harvested sea salt. The experiment included four seawater treatments, differentiated by the presence of microplastics and autoclaving: microplastic-free seawater (MFSW), autoclaved microplastic-free seawater (AMFSW), autoclaved microplastic-containing seawater (AMCSW), and microplastic-containing seawater (MCSW). In vitro testing revealed that microplastics increased biofilm concentration and thickness by significantly inhibiting bacterial dispersion; while dispersion occurred multiple times in microplastic-free groups (MFSW, AMFSW), it was reduced to only one or two events in microplastic-containing groups (AMCSW, MCSW). Biofilm concentration surged in microplastic groups, increasing from 1.8 % to 95.3 % in AMCSW and 2.23 % to 80.23 % in MCSW within 24 h. Ovoviviparous reproduction was significantly reduced in AMFSW (17 ± 1.12 ind·d^-1) and MFSW (23 ± 1.15 ind·d^-1). In vivo tests showed microplastics depressed growth parameters and survival in brine shrimp. In MCSW, protease (0.37 ± 0.07 U/mg protein) and lipase (0.43 ± 0.02 U/mg protein) activities decreased, while AMCSW showed significant increases. Microplastic groups had elevated Vibrio loads in/on brine shrimp, with MCSW peaking at 96.30 ± 8.03 × 10³ CFU g^-1. Furthermore, microplastics caused anatomical and histological abnormalities, including the disappearance of the intestinal epithelial lining and internal swelling in the intestine. In conclusion, our findings showed that the microplastics associated with harvested sea salt can thicken biofilms, hinder antibiotic efficacy, and promote the evolution of antibiotic-resistant strains. A lack of knowledge in this area could lead farmers to overuse antibiotics, posing risks to environment and human health.