SCREENING, IDENTIFICATION AND PHYSIOLOGICAL CHARACTERISTICS OF INTESTINAL BACTERIA AGAINST VIBRIO HARVEYI FROM PENAEUS MONODON

Penaeus monodon (African group) is a new cultured prawn species, which has good development prospects. At present, aquaculture diseases are seriously affecting the health of prawn farming. Based on physiological characteristics of intestinal bacteria in P. monodon, the experimental study was carried out to provide new treatments for acute hepatopancreas necrosis syndrome (AHPND). The dominant intestinal strains in healthy P. monodon were isolated and purified. Using pathogenic Vibrio harveyi as indicator bacteria, antagonistic bacteria were screened from the strains by the Oxford cup method. To identify these antagonistic bacteria, high-throughput sequencing technology was used as the main method. Biolog microbe identification system was also used to identify the strains. These two methods were supplemented by biochemical characteristic tests. To evaluate the safety of antagonistic strains, the drug susceptibility test was carried out in the study. The basic drug resistance information of intestinal bacteria was obtained by this test. According to the drug resistance information, antagonistic strains with high drug sensitivity were selected. The growth curve of the hypersensitive antagonistic strain was plotted to show its growth characteristics. The activity of extracellular enzymes of potential probiotics was calculated. As a result, sixteen dominant indigenous strains were isolated from the intestinal tract of P. monodon. The three antagonistic strains which were named as P.m-1, P.m-9, P.m-13. P.m-1, P.m-9 and P.m-13 were identified as Bacillus subtilis, Enterococcus faecium and Vibrio alginolyticus, respectively. The results of drug sensitivity tests showed that they were not intestinal drug-resistant bacteria, and P.m-1 was highly sensitive to drugs. P.m-1 entered the exponential growth stage from the 2^nd hour, and reached the growth peak at the 10^th hour. The maximum concentration of P.m-1 was 1.14×10⁹ cfu/mL, which indicated that P.m-1 had the strong vitality. After protease activity determination, P.m-1 was considered as a strain that had the strong protease production capacity, which could provide a basis for digestion or purification of the environment. P.m-1 has the potential to become probiotics, which could contribute to the prevention and treatment of acute hepatopancreas necrosis syndrome. The experiment would provide the theoretical basis for functional feed additives from the perspective of intestinal microecology.