Isolation,Identification,Screening And Biological Characterization Analysis Of Bacillus Natto

Bacillus natto is a bacterium that is allowed as a feed additive by the Ministry of Agriculture of China and can be developed as an ideal microecological preparation.In this paper,B.natto was isolated and identified from different sources.The candidate strains were screened by a bacteriostatic test in vitro and subjected to a nattokinase fibrinolytic activity test,and their biological characteristics of heat tolerance,salt tolerance and acid resistance were studied.Then,the antibacterial effect was tested in vivo by animal experiments to screen a B.natto strain for clinical application.First,B.natto was isolated from different sources,and 9 strains were identified based on their colony morphology,microscopic examination,biochemical tests,molecular biology tests and natto fermentation experiments.Second,for screening the best strain of B.natto,the fibrinolytic properties of nattokinase produced by different strains of B.natto were compared,and the antibacterial effects against Salmonella typhimurium,Escherichia coli,Staphylococcus aureus and Candida albicans were detected by bacteriostatic testing in vitro.The results showed that there were no significant differences in fibrinolytic activity among the 9 strains of B.natto isolated in this study.A comprehensive comparison showed that strain N5 had the best inhibitory effect on pathogenic bacteria.Therefore,strain N5 was retained for subsequent studies.In order to study the biological characteristics of B.natto,this article researched on the tolerance of B.natto N5 to temperature,pH and bile salt concentration.The heat resistance test showed that the survival rate of B.natto strain N5 was more than 20%when heated at 80?,90?,and 95? for 1 min and 2 min.The results of the acid resistance test showed that the number of viable bacteria of B.natto decreased gradually with increasing acidity.When the pH was 3,the survival rate of B.natto was 1.1%,and when the pH was 1.5,B.natto had a survival rate of 0.3%,indicating that the B.natto strain N5 is resistant to acid to a certain level under low pH conditions.The experimental results showed that B.natto has a certain survival rate when the bile salt concentration is 0.1%?0.5%,and the viable count was above 1×104 cfu/mL.In the animal experiments,four groups(the negative group,the positive group,the B.natto group and the amoxicillin group)were divided to investigate the bacteriostatic effect of B.natto on salmonella typhimurium in chickens.The experimental result indicated that,B.natto displays inhibition on salmonella typhimurium in chickens.On the third and sixth days after salmonella infected in chickens,the MPN value for salmonella detected in both the B.natto group and the amoxicillin group was lower than that in the positive control group.the B.natto group and the amoxicillin group had significant inhibitory effects on S.typhimurium compared with the positive control group,and the inhibitory effect of the B.natto group was more obvious.