The antagonistic effect and protective efficacy of gram-positive probiotics Bacillus coagulans to newly identified pathogens Pseudomonas aeruginosa in crucian carp Carassius auratus gibelio

Abstract

Pseudomonas aeruginosa is a common gram-negative pathogen belonging to the Aeromonas genus. In the present study, dominant bacteria were isolated from diseased crucian carp (Carassius auratus gibelio). The isolate was identified as P. aeruginosa based on biochemical identification and 16S rDNA sequencing. In the histological observation of diseased C. auratus, a large number of vacuoles and inflammatory infiltration appeared in the liver, the structure of intestinal villi was loose, and a large number of inflammatory cells and vacuoles were found in gill. Five virulence genes exoU, exoS, pcrV, exoT and exoY were identified in this P. aeruginosa isolate. Drug sensitivity testing showed that the isolate was susceptible to norfloxacin, ofloxacin and ciprofloxacin. The supernatant of Bacillus coagulans NJ3 exhibited a significant bactericidal effect on isolated P. aeruginosa based on the inhibition zone experiment. The accumulative mortality of C. auratus caused by P. aeruginosa infection could be significantly reduced by adding B. coagulans NJ3 into the aquaculture water. These results indicated that B. coagulans NJ3 could be used as probiotics to prevent the infections of P. aeruginosa in C. auratus. The present study provided a scientific basis for the identification of P. aeruginosa, and treatment for this pathogen infections in fish by using B. coagulans NJ3.