Abstract: The purpose of this study was to isolate the excellent lactic acid bacteria which could be used for both probiotics and silage starter.Silage was collected in large-scale cattle farm.The gradient diluent was coated on MRS plate for anaerobic culture.The dominant strains were screened and their colony morphology was observed.Biochemical test and specific PCR identification were carried out.The growth curve,acid production curve,the influence of culture temperature and initial pH of the medium on the growth of the self-screened lactic acid bacteria,and its bacteriostatic characteristics,antibiotic sensitivity and safety were studied.The results showed that a bacterial colony with round shape,neat edges,smooth surface,milky white,Gram-positive and non-bacillus bacillus was screened.The biochemical results showed that the strain could grow in the anaerobic environment.The results of exercise test,catalase test,nitrate reduction test,gelatin liquefaction test,indole test were negative.The results of 15 kinds of sugar and alcohol fermentation in keeping with the biochemical characteristics of Lactobacillus casei.The strain was identified by PCR method with specific primers of Lactobacillus casei,agarose gel electrophoresis imaging showed a specific amplified band at 727 bp,which was consistent with the biochemical identification results,and the strain was named as RS1.The pH of the fermentation broth of RS1 did not change significantly at 0 to 4 h,and was in the growth delay period.The pH of the fermentation broth decreased rapidly at 4 to 16 h and entered the logarithmic growth phase.The fermentation broth was in the logarithmic growth phase at 16 to 36 h.The pH dropped slowly and entered a stable period.RS1 could grow in the culture temperature range of 20 to 50 ℃,and the suitable growth temperature was 25 to 40 ℃.It could grow under the initial pH of the culture medium 1.0 to 9.0,and the optimum pH was 6.0 to 8.0.The diameter of the inhibition zone of Staphylococcus aureus was 23 mm,and that of Escherichia coli was 17 mm.It was resistant to enrofloxacin and ceftazidime.After 14 days of administering the mice,the growth status of mice was good.These results indicated that Lactobacillus casei RS1 was safe and non pathogenic,and had potential development value in the field of probiotics and biological feed additives.

Key words: Lactobacillus casei; biological characteristics; antibacterial effect