Selection and Antagonistic Activity of Potentially Probiotic Lactic Acid Bacteria against Vibrio parahaemolyticus Causing Acute Hepatopancreatic Necrosis Disease (AHPND) in White-leg Shrimp

The present study aimed to select the strains of Lactic Acid Bacteria (LAB) that can antagonize Vibrio parahaemolyticus and to use these strains in preventing AHPND in culture shrimp. The research contents embraced the following four things: (1) Isolating, classifying and screening LAB strains based on determinations of morphological, physiological and bio-chemical characteristics; (2) The investigations of their antagonism against V. parahaemolyticus of LAB strains by using the agar well diffusion method; (3) The effects of dietary LAB additives on the death rate and resistance of the white-leg shrimps to AHPND; (4) Identifications of the LAB strains that have great resistance to AHPND in white-leg shrimp. By using the agar well diffusion method, the findings indicated that five out of 94 isolated LAB strains showed the highest antagonizing ability against V. parahaemolyticus strain with an inhibition zone diameter oscillating from 17.5 to 18.5 mm. Also, the death rates of the white leg shrimps in the treatments on which the shrimps were challenged with AHPND strain and fed with the LAB1, LAB2 and LAB5 supplemented feed, were significantly lower than that in the positive control treatment (54.43%), but not significantly higher than that in the negative control treatment (12.23%) in the period of 16 days after treatment. However, the histological images of shrimp hepatopancreas indicated that the infected rate by V. parahaemolyticus significantly reduced from 60.0% to 11.1% in shrimps fed with LAB-supplemented feed as compared to those in the positive control treatment (shrimps were challenged with the harmful bacteria without feeding with LAB-supplement feed). To confirm the identification of above five the best LAB strains, sequencing 16S rRNA gene was conducted. The result showed that LAB1 strain was Lactobacillus plantarum, LAB2 strain was Pediocococcus pentosaceus 1, LAB3 strain was L. garvieae, LAB4 strain was P. pentosaceus 2 and LAB5 strain was L. fermentum.