Screening and identification of lactic acid bacteria with anti- Listeria monocytogenes from traditional fermented food in western Liaoning province

Objective: To isolate lactic acid bacteria( LAB) from traditional fermented foods in western Liaoning province,with outstanding inhibitory activity against Listeria monocytogenes. Methods: LAB with anti-L. monocytogenes were screened by double agar diffusion methods. The antibacterial substance was analyzed using acid test,heat- treated test and protease sensitivity test,the forming process of antibacterial substance was analyzed by growth curve,the integrity of cellular structure was observed by scanning electron microscope. The strains were identified by biochemical characteristics and 16 S rRNA sequence analysis. Results: Strain DL3 with outstanding inhibitory activity against L. monocytogenes was screened from 13 strains LAB,and the antibacterial substance mainly existed in cell- free supernatants( CFS).The inhibitory activity of CFS lost 27.50% by treating with pepsin,and inhibitory activity entirely lost by treating with trypsin and papain.The antibacterial activity of CFS still remained 96.88% by thermal treatment under 121 ℃ for 15 min,and was effective within p H2.5~ p H6.5.The inhibitory substance of strain DL3 produced was preliminary determined as bacteriocin. The growth curve of L.monocytogenes lag phase and stationary phase were extended four hours by mixing CFS of LAB,which significantly shorted the logarithmic growth of L.monocytogenes.Observation under scanning electron microscope revealed that cell of L. monocytogenes became smaller and edge blur,and an apparent hole at one of the cell poles with intracellular component leakage. Strain DL3 was identified as Lactobacillus plantarum. Conclusion: Lb.plantarum DL3 with outstanding inhibitory activity against L. monocytogenes was screened,and its antibacterial substance was preliminary determined as bacteriocin. The strain DL3 had great application prospects on thedevelopment of natural bio- preservative.