Cultural conditions and nutritional components affecting the growth and bacteriocin production of Lactobacillus plantarum KC21

Growth Kinetics of Probiotic Lactobacillus Strains in the Alternative, Cost-Efficient Semi-Solid Fermentation Medium

The growing need for Lactobacillus bacteria usage in industry and the expending probiotic market led to a search for new cost-efficient fermentation media from which a high yield of these bacteria could be obtained. The following study aimed to elaborate cultivation medium, for Lactobacillus spp. growth, which main components would be wheat, maize, barley, and rye flours. The optimal temperature for Lactobacillus growth in new semi-solid fermentation (SSF) medium, water content, and pH of the medium were analyzed by the plate count method. It was established, that the highest bacteria counts were obtained from cultures conducted in the SSF medium with flours to water ratio of 1:1.5 with a natural pH of 6.0 at 37 °C. Subsequently, the growth kinetics of analyzed strains, in both MRS and the SSF media, were studied. The newly designed media contributed to the increased duration of selected Lactobacillus strains lag phase, which varied from 1.98 to 5.64; nevertheless, the maximum growth rate of the strains was two times higher in the SSF medium rather than in MRS, which also resulted in shorter generation time. The developed medium has the potential to become a new cost-efficient fermentation medium for Lactobacillus spp.

Purification and characterization of nisin P produced by a strain of Streptococcus gallolyticus

Introduction. Against the backdrop of increasing resistance to conventional antibiotics, bacteriocins represent an attractive alternative, given their potent activity, novel modes of action and perceived lack of issues with resistance.Aim. In this study, the nature of the antibacterial activity of a clinical isolate of Streptococcus gallolyticus was investigated.Methods. Optimization of the production of an inhibitor from strain AB39 was performed using different broth media and supplements. Purification was carried out using size exclusion, ion exchange and HPLC. Gel diffusion agar overlay, MS/MS, de novo peptide sequencing and genome mining were used in a proteogenomics approach to facilitate identification of the genetic basis for production of the inhibitor.Results. Strain AB39 was identified as representing Streptococcus gallolyticus subsp. pasteurianus and the successful production and purification of the AB39 peptide, named nisin P, with a mass of 3133.78 Da, was achieved using BHI broth with 10 % serum. Nisin P showed antibacterial activity towards clinical isolates of drug-resistant bacteria, including methicillin-resistant Staphylococcus aureus, vancomycin-resistant Enterococcus and penicillin-resistant Streptococcus pneumoniae. In addition, the peptide exhibited significant stability towards high temperature, wide pH and certain proteolytic enzymes and displayed very low toxicity towards sheep red blood cells and Vero cells.Conclusion. To the best of our knowledge, this study represents the first production, purification and characterization of nisin P. Further study of nisin P may reveal its potential for treating or preventing infections caused by antibiotic-resistant Gram-positive bacteria, or those evading vaccination regimens.

Analysis of the antimicrobial activity of Lactobacillus plantarum YM-4-3: implications of suitable conditions for extending the shelf life of fermented soybean products

Lactobacillus (Lb.) plantarum is typically used as a starter culture in salt-fermented foods. Here we report 3-4% NaCl reducing the antimicrobial activity of Lb. plantarum strain YM-4-3, owing to the decrease of bacterial growth, plantaricin activity and expression levels of plantaricin biosynthesis-related genes (PBGs). Meanwhile, 1% NaCl promoted slightly the growth of YM-4-3 and up-regulated the expression of PBGs to the greatest level. The results from a spoilage experiment of fermented soybean products revealed that the 1% NaCl and YM-4-3 treatment group had the longest shelf life representing the minimum number of pathogenic bacteria and the lowest degree of mildew. Therefore, a combination of Lb. plantarum with a low concentration of salt, such as 1% NaCl, is a recommended condition for preparing fermented foods.

Characterization of a broad spectrum bacteriocin produced by Lactobacillus plantarum MXG-68 from Inner Mongolia traditional fermented koumiss

An agar well diffusion assay (AWDA) was used to isolate a high bacteriocin-producing strain with a broad spectrum of antibacterial activity, strain MXG-68, from Inner Mongolia traditional fermented koumiss. Lactobacillus plantarum MXG-68 was identified by morphological, biochemical, and physiological characteristics and 16S rDNA analysis. The production of antibacterial substance followed a growth-interrelated model, starting at the late lag phase of 4 h and arriving at a maximum value in the middle of the stationary phase at 24 h. Antibacterial activity was abolished or decreased in the presence of pepsin, chymotrypsin, trypsin, proteinase, and papain K. The results showed that antibacterial substances produced by L. plantarum MXG-68 were proteinaceous and could thus be classified as the bacteriocin, named plantaricin MXG-68. The molar mass of plantaricin MXG-68 was estimated to be 6.5 kDa, and the amino acid sequence of its N-terminal was determined to be VYGPAGIFNT. The mode of plantaricin MXG-68 action was determined to be bactericidal. Bacteriocin in cell-free supernatant (CFS) at pH 7 was stable at different temperatures (60 °C, 80 °C, 100 °C, 121 °C for 30 min; 4 °C and - 20 °C for 30 days), as well as at pH 2.0-10.0. Antibacterial activity maintained stable after treatment with organic solvents, surfactants, and detergents but increased in response to EDTA. Response surface methodology (RSM) revealed the optimum conditions of bacteriocin production in L. plantarum MXG-68, and the bacteriocin production in medium optimized by RSM was 26.10% higher than that in the basal MRS medium.

Fermentation factors influencing the production of bacteriocins by lactic acid bacteria: a review

Lactic acid bacteria (LAB) are the major interest in food industry primarily by virtue of their biopreservative properties.

Short communication: Bacteriocin KC24 produced by Lactococcus lactis KC24 from kimchi and its antilisterial effect in UHT milk

The severity of Listeria monocytogenes infections emphasizes the need for prevention or elimination of the pathogen from dairy products. Lactococcus lactis KC24, isolated from kimchi, exhibited an antimicrobial effect against food pathogens, including L. monocytogenes ATCC 15313. Lactococcus lactis KC24 was cultured in a 5-L jar fermenter at 35°C, and bacteriocin activity was maximal at 4 h of incubation and persisted for 20 h. Bacteriocin KC24 was inactivated by protease XIV, indicating that it has a proteinaceous nature. Bacteriocin activity was maintained at pH 3.0 to 9.0 and at temperatures of 50 to 121°C. The mode of inhibition against L. monocytogenes ATCC 15313 was shown to involve a bactericidal effect by treatment with 100 and 200 arbitrary units (AU)/mL of bacteriocin KC24. To test the activity of bacteriocin KC24 in a food product, bacteriocin KC24 and nisin (100 and 200 AU/mL) with 4 log cfu/mL of a mixed culture of L. monocytogenes (ATCC 15313, ScottA, H7962, and H7762) were applied to UHT milk. Compared with the control, treatment with bacteriocin KC24 completely inhibited the growth of L. monocytogenes and resulted in no detectable L. monocytogenes after 14 d at 4°C, whereas nisin moderately inhibited L. monocytogenes, resulting in a final concentration after 14 d at 4°C higher than the initial inoculum. Bacteriocin KC24 may prove useful in improving the safety of dairy products.