| In recent years, antibiotics are badly overused in the animal industry, causing the loss of the resistance and the performance of animals, the enhancement of drug resistance of enteric pathogen and the accumulation of medicine residue in animal foods. These harm can cause many food safety problems, seriously affecting human health and agriculture industry development. Therefore, it is extremely urgent to develop new types of feed additive without residue. Probiotics has the advantage of non-pollution, non-toxicity and non-residue and is considered as the best effective substitute to the antibiotics.Based on theoretical foundation for developing probiotics, the biological characteristics of B. laterosporus S62-9 in vitro was studied in this paper. The main results were as following:(1)The growth curve of B. laterosporus S62-9 was determine in nutrient broth at 37 ℃, 240 r/min. The result showed the growth of B. laterosporus S62-9 in NB medium entered exponential phase after 4 hours culture and reached the stationary phases at 14 hours, then the colony amount no increased, which presented a typical microbial growth regularity.(2)The antibacterial spectrums of B. laterosporus S62-9 were researched by the plate confront culture method and the results showed B. laterosporus S62-9 was strongly antagonistic against a range of Gram-negative and Gram-positive bacteria, such as staphylococcus aureus, streptococcus, Listeria monocytogenes and Escherichia Coli, and the inhibitory effect on G+ was stronger than G-.(3)The submerged co-culture assay was used to investigate the abilities of B. laterosporus S62-9 for inhibiting the growth of two pathogen bacteria(Micrococcus luteus 28001 and E. coli 44752). The results showed B. laterosporus S62-9 displayed strong antibacterial activities in co-incubation experiment, and the inhibitory effects were enhanced with the increase of the inoculum rate of B. laterosporus S62-9. Moreover, the antibacterial mechanisms of B. laterosporus S62-9 were nutrition competition and antibacterial peptide antagonism.(4)The experiment also focused on B. laterosporus S62-9 tolerances to the heat and gastrointestinal tract. The results showed the survival rate was 86.2% at 85 ℃ for 5 min, in addition, the survival rate was 88.9% in the gastric juice of p H 2.0 for 4 h, while, the strain showed a survival rate of 90.0% in the intestinal juice plus 0.3% bile for 4 h. Therefore, B. laterosporus S62-9 had an excellent thermostability, which could reduce losses in the process of granulating, moreover, S62-9 also showed a strong tolerance to miming gastrointestinal transit, which providing favorable conditions for the strain to function in the gut.(5)The paper investigated the adhesive ability of B. laterosporus S62-9 to intestinal epithelial cells Caco-2 in vitro, and the results showed that the number of adhered B. laterosporus S62-9 per Caco-2 cell was 20.7 CFU/cell, which revealed that strain S62-9 performed a good adhesion property.(6)The antibiotics sensitivities of B. laterosporus S62-9 were determined using the standard broth microdilution method, and the results showed the strain had no marked resistance to the 10 commonly used veterinary antibiotics, therefore, it was considered to be a biosafety strain.In conclusion, B. laterosporus S62-9 had broad antibacterial spectrums and strong antibacterial properties, and it also had strong tolerances on heat and gastrointestinal tract, in addition, it also had the potential adhesion to the gut epithelial tissue and was considered to be a biosafety strain. Therefore, B. laterosporus S62-9 possessed the probiotics standards and requirements could be used as the excellent strain for probiotics. |
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