| Over the past ten years,the total output of domestic aquatic products has continued to rise,and the annual output has exceeded 60 million tons for three consecutive years.It was found that the use of Chinese herbal medicine and probiotics could reduce the use of antibiotics and effectively reduce the risk of drug residues in aquaculture.Therefore,in recent years,the research of antibiotic substitution in aquaculture has received more and more attention.In this study,a Bacillus strain with good safety and probiotics was screened,and the effect of culture and quality safety were evaluated.The main results are as follows:1.A Bacillus strain with good bacteriostatic effect was isolated from soil samples taken from Nanchen Fishpond in Luoyang.The size of the bacterium was about 0.762±0.076×2.37±0.351?m,which had good bacteriostatic effect on six common pathogenic bacteria,Vibrio hydrophila,Vibrio harveyi and Vibrio alginolyticus.The colony shape is oval,Milky white,and the surface of the colony is rough and opaque.The strain was identified as Bacillus subtilis by physiological and biochemical indices and 16S rDNA molecular biological identification.Its preservation number is CGMCC 17305.The strain could be cultured in 3 g/L starcht,10 g/L peptone and 5 g/L sodium chloride medium for 2 hours,then entered a rapid growth stage,and entered a stable stage for 8 hours.The concentration of bacterial solution reached 10~9 CFU/mL.2.Safety and probiotic characteristics of Bacillus subtilis CGMCC 17305.The susceptibility of the bacteria to ceftriaxone sodium,florfenicol,sulfadiazine sodium,sulfamethoxacil sodium,ofloxacin,lincomycin hydrochloride,gentamicin sulfate,norfloxacin,thiamphenicol,neomycin sulfate and enrofloxacin was studied by cup-plate method.The results showed that the bacteria showed obvious susceptibility to the above 11 antibiotics.The adherence test showed that the adherence rate of the bacteria to fish intestine was 42.05±0.14%,which indicated that the bacteria could be effectively colonized in the intestine of aquatic animals.The survival rate of 4 h treated in acidic environment of pH 5 was 89±9.4%.The 4 h treatment of 4 h in pig bile salt with a concentration of 0.9%still had a survival rate of 46.5±8.3%.At the same time,the bacteria also showed the activity of protease,lipase,amylase,cellulase and other hydrolytic enzymes.3.Aquaculture results and quality and safety evaluation.The microbial powder with a concentration of 10 billion CFU/g was prepared and added to aquaculture feed in a certain proportion.Tilapia and Penaeus vannamei were cultured.Survival rate,daily gain,diet coefficient and fatness were taken as the evaluation indexes of culture effect.The results showed that adding 1%bacterial powder in feed could effectively improve the growth performance of tilapia and Penaeus vannamei.The survival rate of tilapia pond cultured for about 100 days was 95%,significantly higher than that of control group;daily gain of 3.55 g was 1.74 g higher than that of normal culture group;diet coefficient decreased by 0.28;and the survival rate of Penaeus vannamei pond cultured for about 85 days was 13%higher than that of normal culture,daily gain was0.04 g higher and diet coefficient decreased by 0.14.Drug residues in tilapia and Penaeus vannamei were detected after culture.The results showed that 14 kinds of drugs such as malachite green,chloramphenicol,sulfonamides,metronidazole and oxytetracycline were not detected in tilapia and Penaeus vannamei Cultured with Bacillus subtilis CGMCC 17305,which effectively ensured the quality and safety of aquatic products. |
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