Biochemical and Molecular Characterization of Pathogenic Vibrio Associated with White Feces Syndrome in Penaeus vannamei and their Antibiotic Susceptibility

Abstract

White gut disease (WGD) is an emerging threat to shrimp aquaculture, significantly impacting production and profitability. This study aimed to investigate the bacterial diversity associated with WGD in shrimp and antibiotic susceptibility. The total bacterial count (TBC) and total Vibrio count (TVC) were determined in digestive tracts and haemolymph of both Normal and WGD-affected shrimp. The TBC and TVC in the digestive tracts of WGD-affected shrimp were substantially higher (1.5×10⁸ CFU/g and 1.41×10⁷ CFU/g) compared to Normal shrimp (2×10⁵ CFU/g and 0.43×10⁴ CFU/g). Similarly, in haemolymph, TBC and TVC in WGD-affected shrimp (0.6×10⁸ CFU/ml and 0.62×10⁶ CFU/ml) were elevated relative to healthy shrimp (0.51×10⁵ CFU/ml and 0.27×10⁵ CFU/ml). A total of seven distinct bacterial isolates (V1-V7) were isolated from WGD-affected shrimp and characterized based on morphological, biochemical, and molecular analyses. Molecular characterization through 16S rRNA gene sequencing confirmed species as Providencia stuartii, Vibrio campbellii, Vibrio alginolyticus, Shewanella algae and Shewanella carassii. Shewanella carassii was identified as the same species but with different strains. Antibiotic susceptibility testing revealed isolates Vibrio campbellii, Vibrio alginolyticus, Shewanella carassii exhibited resistance to Penicillin-G, and Vibrio alginolyticus, Shewanella carassii resistance to Ampicillin whereas Providencia stuartii exhibited resistance to Tetracycline and Furazolidone. These findings highlight the pathogenic bacterial community associated with WGD and underscore the need for effective disease management strategies in shrimp aquaculture.