Identification of Pathogenic Vibrio Species Associated with Eastern Oyster Crassostrea virginica Larval Mortality Events and Assessment of Potential Therapeutic Approach

Author

Caleb B. Cavness, Louisiana State University and Agricultural and Mechanical CollegeFollow

Semester of Graduation

Summer 2025

Degree

Master of Environmental Studies (MES)

Department

Department of Environmental Sciences

Document Type

Thesis

Abstract

As the aquaculture industry continues to grow it is imperative to identify potential pathogens and find treatments for stock diseases that are both effective and environmentally friendly. The aquaculture of Eastern oysters is plagued by outbreaks of vibriosis during summer months and hatcheries are at risk of larval mortality if pathogenic Vibrio concentrations get too high. Given the success of Bdellovibrio and like organisms (BALOs) in treating V. parahaemolyticus infections in shrimp, we investigated whether BALOs could reduce larval oyster mortality. We collected water samples during two larval mortality events of the Eastern oyster, Crassostrea virginica, in July, 2022, and August, 2024 to isolate Vibrio spp. We purified these isolates and classified them using 16S rDNA sequencing techniques at the LSU Genomics Core Lab. Multiple Vibrio isolates from the two mortality events were selected for pathogenicity screening, LD50 determination, and BALOs treatment trials based on the sequencing results and a literature review. Two additional Vibrio strains from a previous collection stored in our lab were also included in the studies. These selected isolates belonged to V. tubiashii, V. parahaemolyticus, and V. cidicii, V. harveyi, V. azureus, and P. chinensis. V. cidicii isolates LT28 and SW1-15 stood out as highly pathogenic to larvae. Larval mortality was reduced when Vibrio spp. was treated with BALOs. In two pathogenicity studies, LT28 caused 84.17% and 100% mortality, respectively. V. tubiashii (BS10 isolate) was the most pathogenic Vibrio in LD50 assays with a 24-hour LD50 of 2.13 ± 0.3 x 10⁴ CFU/mL. Other Vibrio spp. did not surpass 6.07 x 10⁴ CFU/mL in 24-hour LD50 studies. In challenge studies, BALOs treatment reduced V. cidicii (LT28) mortalities by 18.98% over 48 hours (p< 0.05). V. cidicii (SW1-15) also responded positively to BALOs treatment; mortality was reduced by 18.38% and 27.67% over 24 and 48 hours, respectively (p< 0.05 and p< 0.005 respectively). Our studies indicate the potential for BALOs to be used as a probiotic additive for larval oyster systems in the Northern Gulf of America.

Date

7-29-2025

Recommended Citation

Cavness, Caleb B., "Identification of Pathogenic Vibrio Species Associated with Eastern Oyster Crassostrea virginica Larval Mortality Events and Assessment of Potential Therapeutic Approach" (2025). LSU Master's Theses. 6202.
https://repository.lsu.edu/gradschool_theses/6202

Committee Chair

Hou, Aixin