Objective To explore the antagonistic ability of probiotic D-19 fermentation broth against pathogenic Entero-coccus,evaluate its antagonistic stability from multiple aspects,and provide a theoretical basis for exploring its potential probiotic properties and medical applications as microecologics.Methods Kirby-Bauer method was used to explore the antagonistic ability of probiotic D-19 fermentation broth against Enterococcus faecalis and Enterococcus faecium.The fer-mentation conditions of it were optimized and the antagonistic stability was observed from viewpoints of physicochemical factors and preservation conditions.The antibacterial mechanism of probiotic D-19 was studied through biofilm formation experiments.Results The fermentation broth of probiotic D-19 and the supernatant of sterile bodies could inhibit the growth of E.faecalis and E.faecium,while the bacterial bodies themselves had no significant antibacterial effect.Under the optimized conditions of 1％inoculation in the culture medium,initial pH 7,and 24 hours of cultivation at 37 ℃,the fer-mentation broth of probiotic D-19 showed strong antagonistic ability against the two Enterococcus,with inhibition zone diameter of(24.70±0.71)mm and(22.57±0.43)mm against E.faecalis and E.faecium,respectively.At 40-50 ℃,there was no significant change in the ability of probiotic D-19 fermentation broth to antagonize E.faecalis and E.faecium.As the temperature and treatment time increased,its antagonism gradually decreased until finally lost.Similarly,probiotic D-19 fermentation broth exhibited stable antagonistic ability at pH 5-8.If the pH falls below or exceeds this range,it will gradually lose its antagonistic ability to E.faecalis and E.faecium;When the storage temperature was-20 ℃ and m=5,the antibacterial zone diameter of probiotic D-19 fermentation broth against E.faecalis and E.faecium decreased to(7.56±8.20)mm and(5.64±0.32)mm,respectively;When stored at a temperature of 4 ℃ and d=75,the size of inhibition zone against E.faecalis and E.faecium decreased to(10.02±0.91)mm and(6.62±0.55)mm,respectively;When the stor-age temperature was 25 ℃ and d=1 5,the size of inhibition zone against E.faecalis and E.faecium decreased to(8.26±0.42)mm and(5.99±0.35)mm,respectively.Co-cultivation of probiotic D-19 fermentation broth and two Enterococcus could significantly inhibit the formation of Enterococcus biofilm.Conclusion Probiotic D-19 fermentation broth has strong ant-agonistic ability against E.faecalis and E.faecium under optimal fermentation conditions,and the main antibacterial active ingredient is sterile supernatant.The sterile supernatant has certain acid-base stability and thermal stability,and can main-tain stable antagonistic ability in pH 5-8 and 40-50 ℃ environments.It is sensitive to strong acids,strong alkali and high heat.It can maintain antagonistic activity for 1-5 months under-20 ℃ conditions and not suitable for long-term storage at room temperature or 4 ℃.
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