Research On Screening Of Bacteriocin-producing Strain And Characterization Of The Bacteriocin

Lactic acid bacteria (LAB) produce a number of antimicrobial substances, such asbacteriocins, organic acid, hydrogen peroxide and diacetyl and play an important role in foodpreservation. The aim of this project was to screen and identify the lactobacillus strainsproducing bacteriocin and study the optimal conditions of bacteriocin fermentation and thebacteriocin characteristics. In this study, antimicrobial activity was determined by the oxfordplate assay system.Lactic acid bacteria, isolated from traditional fermentation food, were screened for theproduction of bacteriocins. With the first screening,27of the56isolates inhibited the growthof Staphylococcus aureus AS1.72, Escherichia coli AS1.543, Bacillus subtilis AS1.308. Oneof these strains was classified as Lactobacillus. brevis P-347, the cell-free supernatant ofwhich showed antimicrobial activity to the growth of the indicator strains under theconditions of excluding the effect of organic acids and hydrogen peroxide, but lostantimicrobial activity in the presence of trypsin and papain, confirming that growth inhibitionwas caused by a bacteriocin.Maximum antimicrobial activity (i.e. inhibition zone in26.5mm) was recorded in MRSbroth after24h at30℃by determining the bacteriocin fermentation course of P-347strain.Optimal fermentation conditions for bacteriocin production of P-347strain had beenestablished:2%glucose as carbon source, l%casein peptone as nitrogen source, at initialpH6.5after24h at30~37℃(i.e. inhibition zone in32.5mm). Furthermore, associativecultivation of the P-347strain with Listeria monocytogenes CMCC34005resulted inincreased bacteriocin production.The bacteriocin produced by P-347strain remained active after2h at100℃and after2hof incubation at pH2.0~6.0. No loss in activity was recorded after treatment with ethanol（2~8%, v/v）, NaCl (2~6%, w/v) or surfactants (0.5~1.5%, v/v) such as SDS, Tween20,Tween80and urea. Significant reduction in antimicrobial activity was observed afterincubation in the presence of NaCl (8%, w/v). The bacteriocin remained active after4weeks’storage, but low temperature (-20~4℃) has no effect. Furthermore, the bacteriocin had a broad antimicrobial spectrum against gram-positive bacteria and gram-negative bacteria, butnot yeast or mold.