Isolated And Screening Of The Dominant Lactic Acid Bacteria From Shrimp Digestive Tract And Study On Application Effect In Shrimp Farming

The study was conducted to screen dominant probiotics for shrimp from Litopenaeus vannamei and Penaeus monodon digestive tract which cultured in Wenchang and Haikou shrimp ponds since Sept.2012to Sept.2013,according to its probiotic safe characteristics,explore its susceptibility testing,optimum growth conditions,application effects and in vivo vitro of vibrio antagonism effects,and evaluate their application effects based on the above-mentioned research results.The density of total cultivable bacteria and lactic acid bacteria in shrimp’digestive tract and hepatopancreas shows that,the average density of total bacteria in hepatopancteas is4.25×108cfu/g,lactic acid bacteria is1.3x108cfu/g;total bacteria density in digestive tract is2.8x109cfu/g,LAB density is4.64x108cfu/g.and the predominant bacteria in shrimp intertinal are mainly lactic acid bacteria(LAB),its proportion of the total bacriera varies from12.90%-27.98%.The optimum growth conditions results shows that the most sutiable pH for four strains of lactic acid bacteria(LAB) is between5.0and6.5,the optimum temperature is25-34,the optimum salinity is10-30,and the most suitableinoculation density is2×108cfu/ml.susceptibility results shows that LAB HN3is highly sensitive to chloramphenicol,cefoperazone and other drugs; LAB HN5is highly sensitive to streptomycin,cefoxitin and other12drugs; LAB HN7is highly sensitive to vancomycin,kanamycin and other15drugs; LAB HN12is highly sensitive to chloramphenicol,ceftriaxone and other drugs.LAB HN3was identified according to its morphological,physiological and biochemical characteristics, the results shows that LAB HN3is safe predominant probiotic for shrimp and is identified as Lactobacillus sp..The feeding experiment results showed that shrimp fed mixing with4×106cfu/g or impregnation with5×104cfu/ml probiotic HN3showed relatively higher daily gain rate(DGR)、survival rate (SR) and specific growth rate(SGR) compared with those fed control diet (P＜0.05). what’s more, we found that the population density of lactic acid bacteria great significantly increased in shrimp digestive tract and culture water compared with control; however, the number of Vibrio reduced greatly. The present results suggested that the diet supplemented with probiotic HN3could improve growth and survival of shrimp, adapt and colonize in the digestive tract of shrimp and environment, and inhibit the growth of Vibrio harveyi and Vibrio parahaemolyticus at the same time. The agar antagonism assay results reported that both bacteria and its extracellular fluid showed significantly inhibitory effects against the growth of Vibrio harveyi and Vibrio parahaemolyticus(P<0.05); The artificial infection experiment results showed that shrimp fed mixing with4×106cfu/g or impregnation with3×104cfu/ml probiotic HN3after equivalent concentration of Vibrio harveyi and Vibrio parahaemolyticus could promote its growth and improve its survival rate.