Partial characterisation of a bacteriocin produced by Leuconostoc mesenteroides A11 and evaluation of bacteriocin production using whey as culture medium

Isolation, Characterization, and Effect on Biofilm Formation of Bacteriocin Produced by Lactococcus lactis F01 Isolated from Cyprinus carpio and Application for Biopreservation of Fish Sausage

The aim of this work was the screening of bacteriocin-producing LABs isolated from fish, the selection of promising/prominent strain(s), the characterization of the bacteriocin produced, and the evaluation of its potential to be used as biopreservative(s). Amplification and sequencing of the 16S rRNA gene of the bacteriocin-producing strain was performed. Then a partial purification of the produced bacteriocin, using a combination of ammonium sulfate and chloroform-methanol precipitation, was done. Its molecular weight was determined by SDS-PAGE. In addition, the action spectrum, the hemolysis test, and its ability to inhibit biofilm formation were analyzed. A total of 88 isolates of lactic acid bacteria (LAB) including one bacteriocin producer, which was identified as Lactococcus lactis F01, were collected. The bacteriocin was partially purified with an estimated yield of 40%. Regarding the SDS-PAGE profile, the secreted bacteriocin has molecular weight of about 3.5 kDa and was identified as class I bacteriocin. The antimicrobial test showed that the bacteriocin inhibits pathogenic and/or spoilage bacteria, 10 Gram-positive and 16 Gram-negative bacterial species. Moreover, it can inhibit biofilm formation from 1.3% (Escherichia coli) to 63.92% (Pseudomonas aeruginosa ATCC15692) depending on the strain. The hemolytic activity of novel bacteriocin was observed at the concentration of 10 μg/ml of bacteriocin crude extract, which was $0.7\pm 0.0029\%$ . In addition, it exhibited good thermal and pH stability with retained antibacterial activity of 85.25% after treatment at 121°C for 20 min, as well as at a pH range between 2.0 and 10.0. Moreover, this bacteriocin showed the ability to inhibit the growth of bacterial culture load in fish sausage stored at 8°C for 28 days. Considering the results obtained, bacteriocin could be potentially exploited as an alternative to chemical preservatives or as a substitute for antibiotics.

Partial purification and characterization of a broad-spectrum bacteriocin produced by a Lactobacillus plantarum zrx03 isolated from infant's feces

Lactobacillus plantarum zrx03 was a bacteriocin-producing strain isolated from infant's feces. The fermentation supernatant produced by this strain could strongly inhibit Escherichia coli JM109 ATCC 67387, Staphylococcus aureus ATCC 25923, and Listeria monocytogenes CICC 21633, in which the diameter of inhibition zone was 12.83 ± 0.62 mm, 15.08 ± 0.31 mm, 6.75 ± 0.20 mm, respectively, compared with lactic acid bacteria N1, N2, M13, M21, M31, and M37. According to amplification of 16S rRNA gene and identification of phylogenetic tree, this strain had a 1,450 bp sequence and 100% identity to the L. plantarum strain. Based on the influence of different protease treatments, such as pepsin, trypsin, papain, and proteinase K on the antimicrobial activity, this antimicrobial substance was considered to be a natural protein. Using bacteriocin produced by this strain as study object of this experiment, it had been extracted from ammonium sulfate precipitation and different organic solvents. The results showed that ethyl acetate was selected as the optimal solution to crude extraction of bacteriocin after comparing ammonium sulfate precipitation method and organic solvent extraction method, such as n-butanol, n-hexane, dichloromethane, trichloromethane, in which the diameter of the inhibition zones was above 28 mm. Results also showed the inhibition spectrum of the obtained bacteriocin had a broad spectrum of inhibition which could inhibit Gram-positive, Gram-negative, yeast. Especially, it could effectively inhibit S. aureus ATCC 25923, Bacillus subtilis CICC 10002, Bacillus anthracis CICC 20443, E. coli JM109 ATCC 67387, and Salmonella CMCC 541, and the zone diameter of inhibition has reached more than 28 mm. Moreover, it had a good thermal stability which antibacterial activity was retained 70.58% after treatment at 121°C for 30 min, and pH-stability was between pH 2.0-9.0. These results suggested bacteriocin produced by L. plantarum zrx03 had potential application prospects in food preservation.