Screening and identification of lactic acid bacteria with excellent antibacterial properties and detection of active substances

Abstract:

[Background] Lactic acid bacteria are widely distributed in human and animals. They are the main force to maintain the balance of gastrointestinal flora and improve immunity. In recent years, as antibiotics are banned to be used as feed supplements for animals, the incidence of animal diseases has been on the rise. An essential solution is to develop new feed supplements based on the characteristics of lactic acid bacteria and their active metabolites. [Objective] To isolate and screen lactic acid bacteria with excellent antibacterial properties from soil and to analyze and evaluate the characteristics of their active metabolites. [Methods] Two acid-producing strains with excellent antibacterial activity were screened with bromocresol purple plate method and Oxford cup method, which were named H-3 and H-4, respectively. After morphological identification and 16S rRNA gene sequencing, the growth curves and acid production of the two strains were detected, respectively. The effective components of antibacterial substances produced by the two strains were analyzed based on acid exclusion, protease treatment, and heat treatment. [Results] H-3 and H-4 were preliminarily identified as Pediococcus acidilactici, which demonstrated good growth performance and acid production capacity. The supernatant of the fermentation broth of the two strains showed obvious inhibitory effect on Escherichia coli, Staphylococcus aureus, Salmonella choleraesuis and Shigella flexneri. At pH 6.0, the supernatant maintained strong antibacterial activity, while at pH 7.4, the antibacterial activity of the supernatant of H-4 disappeared. The antibacterial activity of the supernatant treated with protease decreased or even disappeared, but the high-temperature treatment had little influence on the activity, suggesting the existence of a protein in the antibacterial substances with thermal stability. [Conclusion] H-3 and H-4 have broad-spectrum antibacterial activity, and in addition to organic acids, there is also a protein in the produced antibacterial substances. The result in this study lays a theoretical foundation for the research and development of new green feed supplements and antibiotic alternatives.