抑菌性益生菌菌种的筛选鉴定及抑菌效果研究OA

Given the ban on growth-promoting antibiotics in livestock feeds,this study aimed to screen probiotics with strong antagonistic activity against Escherichia coli and Salmonella for green antibiotic-free breeding.Strains were isolated from the intestinal contents of healthy broilers,followed by primary screening with a double-layer plate method and secondary screening via the Oxford cup assay.The strains were identified by colony morphology,Gram staining and 16S rDNA sequencing,and the effects of inoculation amount and active components on antibacterial activity were investigated.The results showed that six strains with bacteriostatic activity were isolated,among which strains R2 and R5 showed the optimal antibacterial performance.Combined with morphological observation and sequence homology alignment,strain R2 was identified as a Gram-positive short rod-shaped Bacillus,and strain R5 was identified as a Gram-positive spherical Lactococcus(a genus of lactic acid bacteria).In the Oxford cup re-screening test,the net inhibition zone diameters of strain R5 against E.coli and Salmonella were 7.65 mm and 7.40 mm,respectively,which were superior to those of strain R2.The inoculation test showed that the antibacterial effect of R2 had no significant difference within the inoculation range of 5%～25%(P＞0.05);the optimal inoculation amounts of R5 for inhibiting E.coli and Salmonella were 15%and 20%,respectively.The antibacterial substances of R5 were mainly distributed in the fermentation supernatant.The OD600 of the supernatant group was significantly lower than the precipitation and whole bacterial suspension groups(P＜0.05),and the inhibition zone diameters of the supernatant against two pathogens reached 10.10 mm and 7.55 mm,respectively.This study screened a chicken-derived Lactococcus strain R5 with excellent bacteriostatic activity,which provides experimental support for the development of probiotic additives replacing antibiotics.