Influence of pH and temperature on growth and bacteriocin production by Leuconostoc mesenteroides L124 and Lactobacillus curvatus L442

Effects of Fermentation Temperature, Drying Temperature, Caliber Size, Starter Culture, and Sodium Lactate on Listeria monocytogenes Inactivation During Salami Production

The effect of fermentation and drying temperatures, caliber, and sodium lactate on Listeria monocytogenes inactivation was studied in salami, produced in a pilot scale, inoculated with 107 CFU/g of Listeria innocua ATCC® 33090 as a surrogate microorganism for L. monocytogenes. Fermentation temperature varied between 24 and 30°C, drying temperature between 14 and 20°C, caliber between 5.1 and 13.2 cm, and sodium lactate initial concentrations in salamis were 0 and 2%. L. innocua counts, pH and water activity were determined in salamis over time. Sodium lactate (2%) decreased pH drop and Listeria inactivation during fermentation. Baranyi & Roberts equation was used to fit the experimental data and to estimate, for each test condition, inactivation rate (k), initial (Y0), and final counts of L. innocua (YEND). Total inactivation was calculated as Y0 minus YEND (Y0-YEND). Then, using a Box Benkhen experimental design, a quadratic model for k and a two-factor interaction model (2FI) for Y0 - YEND were obtained as functions of fermentation temperature, drying temperature, and caliber size. The models predicted that maximum k and Y0 -YEND, -2.62 ± 0.14 log10 CFU/g/day and 4.5 ± 0.1 log10 CFU/g, respectively, would be obtained fermenting at 30°C and drying at 20°C regardless of caliber. Drying at 14°C allowed Listeria growth until a water activity (aw) of 0.92 was reached. Therefore, if initial Listeria contamination is high (3 log10 CFU/g), drying at low temperatures will compromise product safety.

Dynamic Modelling to Describe the Effect of Plant Extracts and Customised Starter Culture on Staphylococcus aureus Survival in Goat's Raw Milk Soft Cheese

This study characterises the effect of a customised starter culture (CSC) and plant extracts (lemon balm, sage, and spearmint) on Staphylococcus aureus (SA) and lactic acid bacteria (LAB) kinetics in goat's raw milk soft cheeses. Raw milk cheeses were produced with and without the CSC and plant extracts, and analysed for pH, SA, and LAB counts throughout ripening. The pH change over maturation was described by an empirical decay function. To assess the effect of each bio-preservative on SA, dynamic Bigelow-type models were adjusted, while their effect on LAB was evaluated by classical Huang models and dynamic Huang-Cardinal models. The models showed that the bio-preservatives decreased the time necessary for a one-log reduction but generally affected the cheese pH drop and SA decay rates (logD_ref = 0.621-1.190 days; controls: 0.796-0.996 days). Spearmint and sage extracts affected the LAB specific growth rate (0.503 and 1.749 ln CFU/g day^-1; corresponding controls: 1.421 and 0.806 ln CFU/g day^-1), while lemon balm showed no impact (p > 0.05). The Huang-Cardinal models uncovered different optimum specific growth rates of indigenous LAB (1.560-1.705 ln CFU/g day^-1) and LAB of cheeses with CSC (0.979-1.198 ln CFU/g day^-1). The models produced validate the potential of the tested bio-preservatives to reduce SA, while identifying the impact of such strategies on the fermentation process.

Optimization of cultural conditions for enhancement of anti-quorum sensing potential in the probiotic strain Lactobacillus rhamnosus GG against Pseudomonas aeruginosa

Disruption of quorum sensing (QS) system, which is a central regulator for pathogenesis of Pseudomonas aeruginosa, is referring to as quorum quenching (QQ). This study was undertaken to evaluate and enhance the anti-quorum sensing (AQS) potential of probiotic strain Lactobacillus rhamnosus GG. The cell-free supernatant (CFS) of this probiotic strain showed anti-quorum sensing activity against Pseudomonas aeruginosa, which was determined using well-diffusion agar-plate assay. Anti-quorum sensing potential of L. rhamnosus GG was enhanced by optimization of various cultural conditions using classical and statistical optimization approaches. Six variables were optimized using one-variable-at-a-time (OVAT) method. Four significant variables, viz., temperature, pH, incubation time, metal ion, and its concentration, were chosen for further optimization by response surface methodology (RSM) using central composite design (CCD). Analysis of variance (ANOVA) demonstrated that the regression model is highly significant, as indicated by F test with a low probability value (p  < 0.0002) and high value of coefficient of determination (0.8738) and also had significant influence on the generation of anti-quorum sensing effector molecules. Maximum production of anti-quorum sensing activity, in terms of zones of inhibition, was achieved under the following optimized conditions such as 37 °C temperature, pH 6.5, incubation time 24 h, and 2.5 mM concentration of zinc sulfate (ZnSO₄). The quadratic model predicted 1.3-fold increase anti-quorum sensing activity production over un-optimized cultural conditions. The present research is the first report representing the enhancement of anti-quorum sensing potential of L. rhamnosus GG.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-022-03187-2.

The Effect of Incubation Temperature, Substrate and Initial pH Value on Plantaricin Activity and the Relative Transcription of pln Genes of Six Sourdough Derived Lactiplantibacillus plantarum Strains

The aim of the present study was to assess the effect of sourdough related parameters on the growth and plantaricin activity of six Lactiplantibacillus plantarum strains against a mixture of 5 Listeria monocytogenes strains and to analyze the transcriptomic response of their pln genes. Parameters included 3 substrates (MRS broth, mMRS broth, WFE), 3 temperatures (20, 30, 37 °C), 2 initial pH values (5.0, 6.0), 2 NaCl concentrations (0.0, 1.8%) and 12 time points (ranging from 0 to 33 h). The transcriptomic response of the plantaricin genes to the aforementioned parameters was assessed after 21 h of growth. In general, plantaricin activity was strain dependent with that of Lp. plantarum strains LQC 2422, 2441, 2485 and 2516, harboring four pln genes, namely, pln423 (plαA), plαΒ, plαC and plαD, reaching 2560 AU/mL. However, strains LQC 2320 and 2520, in which 18 pln genes were detected, namely, plNC8a, plNC8b, plNC8c, plnL, plnR, plnJ, plnK, plnE, plnF, plnH, plnS, plnY, plNC8-IF, plNC8-HK, plnD, plnI, plnM and plnG, exhibited plantaricin activity barely reaching 160 AU/mL. Substrate, temperature, initial pH value and strains significantly affected plantaricin activity, while NaCl had only a marginal effect. Similarly, growth substrate and temperature had a more pronounced effect than initial pH value on gene transcription. A strong correlation between the transcription of the genes belonging to the same locus was observed; however, only a weak correlation, if any, was observed between plantaricin activity and the transcription of the genes assessed.

The Influence of Environmental Conditions on the Antagonistic Activity of Lactic Acid Bacteria Isolated from Fermented Meat Products

The aim of this study was to determine the impact of environmental conditions on the antimicrobial properties of 21 lactic acid bacteria strains in the selected indicator bacteria. To assess the antimicrobial activity of the whole bacteria culture (WBC), the agar well diffusion method was used. The interference of LAB strains with the growth of the selected indicator bacteria was evaluated by incubating co-cultures in the food matrix. Based on the conducted research, it was found that environmental conditions have a significant impact on the antimicrobial activity of lactic acid bacteria strains. The highest antimicrobial activity was recorded under optimal conditions for the development of LAB, the incubation time being different depending on the indicator strain used. The tested LAB strains were characterized by a high ability to inhibit indicator strains, especially in the food matrix. These results led us to further characterize and purify the antimicrobial compound produced by lactic acid bacteria taking into account changing environmental conditions.

Influence of Culture Conditions and Medium Compositions on the Production of Bacteriocin-Like Inhibitory Substances by Lactococcus lactis Gh1

Antibacterial peptides or bacteriocins produced by many strains of lactic acid bacteria have been used as food preservatives for many years without any known adverse effects. Bacteriocin titres can be modified by altering the physiological and nutritional factors of the producing bacterium to improve the production in terms of yield and productivity. The effects of culture conditions (initial pH, inoculum age and inoculum size) and medium compositions (organic and inorganic nitrogen sources; carbon sources) were assessed for the production of bacteriocin-like inhibitory substances (BLIS) by Lactococcus lactis Gh1 in shake flask cultures. An inoculum of the mid-exponential phase culture at 1% (v/v) was the optimal age and size, while initial pH of culture media at alkaline and acidic state did not show a significant impact on BLIS secretion. Organic nitrogen sources were more favourable for BLIS production compared to inorganic sources. Production of BLIS by L. lactis Gh1 in soytone was 1.28-times higher as compared to that of organic nitrogen sources ((NH4)2SO4). The highest cell concentration (XmX = 0.69 ± 0.026 g·L-1) and specific growth rate (μmax = 0.14 h-1) were also observed in cultivation using soytone. By replacing carbon sources with fructose, BLIS production was increased up to 34.94% compared to BHI medium, which gave the biomass cell concentration and specific growth rate of 0.66 ± 0.002 g·L-1 and 0.11 h-1, respectively. It can be concluded that the fermentation factors have pronounced influences on the growth of L. lactis Gh1 and BLIS production. Results from this study could be used for subsequent application in process design and optimisation for improving BLIS production by L. lactis Gh1 at larger scale.

Potentially Probiotic Lactobacillus Strains Derived from Food Intensify Crystallization Caused by Proteus mirabilis in Urine

Proteus mirabilis is a common cause of infectious urolithiasis. The first stage in the formation of urinary stones is the crystallization of mineral salts in the urine induced by urease activity of this microorganism. Lactobacillus spp. are an important component of the human microbiota and in large quantities occur in foods. Regardless of their origin, those with probiotic properties are proposed as an alternative to antibiotic therapy in the treatment of urinary tract infections. The aim of the study was to check the effect of selected Lactobacillus plantarum and Lactobacillus brevis strains on crystallization caused by P. mirabilis in an in vitro experiment. It has been confirmed that selected Lactobacillus strains have antibacterial properties and colonize the urinary tract epithelium. During 24-h incubation of bacterial cultures, containing P. mirabilis and individual Lactobacillus strains, in synthetic urine, bacterial viability (CFU/mL), pH, and crystallization were determined. Crystallization was assessed quantitatively and qualitatively using AAS and XRD techniques as well as phase-contrast microscopy. It has been shown that in the presence of selected Lactobacillus strains, the culture pH increases faster, especially after 8 h of incubation, compared with the pure P. mirabilis culture. An increase in pH reduces the viability of P. mirabilis; however, in the presence of some lactobacilli, the uropathogen grows more intensively. The presence of Lactobacillus also affected crystallization by increasing its intensity, and the resulting crystals were larger in size. Tested L. plantarum and L. brevis strains could therefore accelerate the formation of urinary stones and development of infection.

Production of Bioactive Peptides from Lactic Acid Bacteria: A Sustainable Approach for Healthier Foods

Traditional fermented foods where lactic acid bacteria (LAB) are present have been associated with beneficial effects on human health, and some of those benefits are related to protein-derived products. Peptides produced by LAB have attracted the interest of food industries because of their diverse applications. These peptides include ribosomally produced (bacteriocins) and protein hydrolysates by-products (bioactive peptides), which can participate as natural preservatives and nutraceuticals, respectively. It is essential to understand the biochemical pathways and the effect of growth conditions for the production of bioactive peptides and bacteriocins by LAB, in order to suggest strategies for optimization. LAB is an important food-grade expression system that can be used in the simultaneous production of peptide-based products for the food, animal, cosmetic, and pharmaceutical industries. This review describes the multifunctional proteinaceous compounds generated by LAB metabolism and discusses a strategy to use a single-step production process, using an alternative protein-based media. This strategy will provide economic advantages in fermentation processes and will also provide an environmental alternative to industrial waste valorization. New technologies that can be used to improve production and bioactivity of LAB-derived peptides are also analyzed.

Antimicrobial activity of nest-lining feathers is enhanced by breeding activity in avian nests

The use of feathers as nest material has been proposed as a kind of self-medication strategy because antimicrobial-producing microorganisms living on feathers may defend offspring against pathogenic infections. In this case, it is expected that density of antimicrobial-producing bacteria, and their antimicrobial effects, are higher in feathers that line the nests than in eggshells. Moreover, we know that feather pigmentation and breeding activity may influence density and antimicrobial production of bacteria. To test these predictions, we analyzed bacterial densities and antimicrobial activity of bacterial colonies isolated from bird eggshells and nest-lining feathers against bacterial strains comprising potential pathogens. Samples were collected from spotless starling (Sturnus unicolor) nests, and from artificial nests to isolate the effects of breeding activity on bacterial communities. The composition of feathers lining the nests was experimentally manipulated to create groups of nests with pigmented feathers, with unpigmented feathers, with both types of feathers or without feathers. Although we did not detect an effect of experimental feather treatments, we found that bacterial colonies isolated from feathers were more active against the tested bacterial strains than those isolated from eggshells. Moreover, bacterial density on feathers, keratinolytic bacteria on eggshells and antimicrobial activity of colonies isolated were higher in starling nests than in artificial nests. These results suggest that antimicrobial activity of bacteria growing on nest-lining feathers would be one of the mechanisms explaining the previously detected antimicrobial effects of this material in avian nests, and that breeding activity results in nest bacterial communities with higher antimicrobial activity.

Characterization, Toxicity, and Optimization for the Growth and Production of Bacteriocin-like Substances by Lactobacillus curvatus

This study aimed to characterize, evaluate toxicity and optimize the conditions for the growth and production of bacteriocin-like substances by Lactobacillus curvatus P99. The antibacterial activity of the cell-free supernatant (CFS) containing bacteriocin-like substances was evaluated by the agar diffusion technique. The stability of the CFS was also examined after heat treatment, refrigeration, freezing, pH variations, and treatment with different chemical substances. The toxic effect of CFS on Drosophila melanogaster diet was determined by calculating the survival rate of the flies. The effects of pH, temperature, and incubation time were the parameters used to optimize cell growth and production of bacteriocin-like substances through response surface methodology. The CFS was stable for 36 weeks under freezing and refrigeration, as well as under heat treatment, in acidic and basic pH and for all chemical substances tested. Fewer than 50,000 AU/mL of CFS added to D. melanogaster diet showed no toxic effect. The optimum growth condition was pH 6.3 at 29.3 °C for 18.6 h, and the optimum production of bacteriocin-like substances was under pH 6.22 at 30.6 °C for 17.9 h. The data on the optimization of cell growth and the characterization and optimization of bacteriocin-like substances provided information to support the industrial-scale production of this microorganism and its metabolites.

Adsorption of plantaricin Q7 on montmorillonite and application in feedback regulation of plantaricin Q7 synthesis by Lactobacillus plantarum Q7

Kieselguhr, bentonite, and montmorillonite were investigated as potential carriers of plantaricin Q7. Highest level of adsorption of plantaricin Q7 was obtained with montmorillonite. Meanwhile, visible inhibition zones were observed against Listeria monocytogenes for montmorillonite adsorbed with plantaricin Q7. Adsorption kinetics showed that the adsorption behaviour followed the pseudo-first-order and Weber's intra-particle diffusion models, suggesting two steps had taken place during the adsorption process. X-ray diffraction assays revealed that plantaricin Q7 was intercalated into the interlayer space of montmorillonites. Electrostatic, hydrogen bonding and hydrophobic interactions proved to play important roles in the mechanisms of interaction between montmorillonite and plantaricin Q7, as shown by infrared spectroscopy analysis. In addition, plantaricin Q7 production was inhibited by feedback regulation with its high concentrations. In order to remove product feedback inhibition in plantaricin Q7 production, a strategy was implemented for its adsorption onto montmorillonite during fermentation. The final plantaricin Q7 output reached 3713.40 IU/mL during fermentation using montmorillonite to adsorb plantaricin Q7, 41.61% higher than that of non- montmorillonite. These results indicate that montmorillonites are suitable carriers for plantaricin Q7 adsorption, and the adsorption of plantaricin Q7 onto montmorillonite during fermentation could be a good method to increase final plantaricin Q7 production.

Artisanal tanneries: Potential application of inoculants formulated with lactic acid bacteria

In artisanal tanneries, the skins are immersed in cereals fermented by natural microbial flora in order to reduce the pH of the skin, an essential condition for carrying out the final step. The environmental thermal variation alters the fermentation process and affects the quality of the final product. The aim of this work was to isolate lactic acid bacteria from cereals mixture fermented in an artisanal tannery and to evaluate in vitro the acidifying activity of the strains as a first step for the formulation of a starter culture. In most samples, a prevalence of cocci (95%) was observed with respect to bacilli. The best acidifying strains were identified by phenotypic and genotypic techniques as Enterococcus faecium CRL 1943 (rapid acidification at 37 °C) and Leuconostoc citreum CRL 1945 (high acidifying activity at 18 °C). In addition, the biomass production of the selected strains was analyzed at free and controlled pH (bioreactors 1.5 L). The production of biomass was optimal at controlled pH, with a higher growth (0.5-1.1 log units). Both strains were compatible, allowing their inclusion in a mixed culture. These lactic strains could contribute to the systematization of the tanning process.

Influence of culture media, pH and temperature on growth and bacteriocin production of bacteriocinogenic lactic acid bacteria

There has been continued interest in bacteriocins research from an applied perspective as bacteriocins have potential to be used as natural preservative. Four bacteriocinogenic lactic acid bacteria (LAB) strains of Lactobacillus curvatus (Arla-10), Enterococcus faecium (JFR-1), Lactobacillus paracasei subsp. paracasei (JFR-5) and Streptococcus thermophilus (TSB-8) were previously isolated and identified in our lab. The objective of this study was to determine the optimal growth conditions for both LAB growth and bacteriocins production. In this study, various growth conditions including culture media (MRS and BHI), initial pH of culture media (4.5, 5.5, 6.2, 7.4 and 8.5), and incubation temperatures (20, 37 and 44 °C) were investigated for LAB growth measured as optical density (OD), bacteriocin activity determined as arbitrary unit and viability of LAB expressed as log CFU ml-1. Growth curves of the bacteriocinogenic LAB were generated using a Bioscreen C. Our results indicated that Arla-10, JFR-1, and JFR-5 strains grew well on both MRS and BHI media at growth temperature tested whereas TSB-8 strain, unable to grow at 20 °C. LAB growth was significantly affected by the initial pH of culture media (p < 0.001) and the optimal pH was found ranging from 6.2 to 8.5. Bacteriocin activity was significantly different in MRS versus BHI (p < 0.001), and the optimal condition for LAB to produce bacteriocins was determined in MRS broth, pH 6.2 at 37 °C. This study provides useful information on potential application of bacteriocinogenic LAB in food fermentation processes.

Enhancement of the productivity of the potent bacteriocin avicin A and improvement of its stability using nanotechnology approaches

Herein, enhancements of the yield and antimicrobial activity duration of the bacteriocin avicin A were accomplished using fractional factorial design (FFD) and layered double hydroxide (LDH) nanoparticles. Firstly, potential factors affecting bacteriocin production were selected for preliminary study. By a 25-1 FFD, high pH was shown to have a positive effect on avicin A yield, while temperature and duration of incubation, as well as peptone nitrogen sources all had negative effects. The highest bacteriocin production and activity (2560 BU/ml) were observed after 30 h of incubation at 30 °C, with pH adjustment at 7, and in the presence of 2 g mannitol as carbon source and 2.2 g peptone as nitrogen source. Secondly, avicin A nanocomposites with different LDH precursors were tested. Only avicin A-ZnAl-CO3 LDH demonstrated a potent antimicrobial activity against Lactobacillus sakei LMGT 2313 that lasted for at least 24 days, as compared to the values of 6 and 15 days observed with the free avicin A that has been stored at room temperature and at 4 °C, respectively. In conclusion, avicin A production and stability can be improved by manipulating the growth conditions and media composition, together with conjugation to LDHs.

Application of high resolution melting assay (HRM) to study temperature-dependent intraspecific competition in a pathogenic bacterium

Studies on species’ responses to climate change have focused largely on the direct effect of abiotic factors and in particular temperature, neglecting the effects of biotic interactions in determining the outcome of climate change projections. Many microbes rely on strong interference competition; hence the fitness of many pathogenic bacteria could be a function of both their growth properties and intraspecific competition. However, due to technical challenges in distinguishing and tracking individual strains, experimental evidence on intraspecific competition has been limited so far. Here, we developed a robust application of the high-resolution melting (HRM) assay to study head-to-head competition between mixed genotype co-cultures of a waterborne bacterial pathogen of fish, Flavobacterium columnare, at two different temperatures. We found that competition outcome in liquid cultures seemed to be well predicted by growth yield of isolated strains, but was mostly inconsistent with interference competition results measured in inhibition tests on solid agar, especially as no growth inhibition between strain pairs was detected at the higher temperature. These results suggest that, for a given temperature, the factors driving competition outcome differ between liquid and solid environments.

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.

Optimization of growth and bacteriocin production by Lactobacillus sakei subsp. sakei2a

Lactobacillus sakei subsp. sakei 2a is a bacteriocinogenic lactic acid bacterium isolated from Brazilian pork sausage, capable of inhibiting the growth of microbial pathogens, mainly Listeria monocytogenes. In order to optimize bacteriocin production for industrial applications, this study evaluated the effect of supplementation of MRS broth with glucose, Tween 20, Tween 80, sodium citrate, potassium chloride and cysteine, and effect of the initial pH and temperature of incubation of the medium on production of bacteriocins by L. sakei 2a. Adding glucose and Tween 20 to the medium, an initial pH of 5.0 or 5.5, and incubation temperatures of 25 °C or 30 °C resulted to the highest bacteriocin yields. Thus, a 2(4) factorial design with the four variables was performed, and statistical analysis showed that it was an adequate model (R (2) = 0.8296). In the studied range, the four parameters significantly influenced bacteriocin production, with the maximum yield produced at an initial pH between 5.5 and 7.0, a temperature between 25 and 30 °C and supplementation of the MRS broth with glucose from 3.25 to 6.0 g L(-1) and Tween 20 from 0.575 to 1.15% (v/v). Response Surface Methodology analysis indicated that the highest bacteriocin production (12800 AU mL(-1)) occurred in the MRS broth supplemented with 5.5 g L(-1) glucose and 1.05% Tween 20 at an initial pH of 6.28 and an incubation temperature of 25 °C. The amount of bacteriocin produced in commercial MRS broths under the same conditions was only 5600AU mL(-1).

Prospects of host-associated microorganisms in fish and penaeids as probiotics with immunomodulatory functions

Aquatic animals harbor a great number of microorganisms with interesting biological and biochemical diversity. Besides serving as the natural defense system of the host, the utilization potential of this microbial association has been identified particularly as reservoirs of candidate probiotics. Host-derived probiotics have gained popularity in recent years as they offer an alternative source of beneficial microbes to the industry that is customarily dependent on the use of terrestrial microorganisms. At present, there is an overwhelming number of candidate probiotics in aquaculture but their large-scale application is restricted by bio-technological concerns and fragmentary documented probiotic actions. This paper presents the current understanding on the use of probiotics as a sustainable alternative that promotes health and welfare in fish and penaeids. In particular, this paper discusses the relevance of host microbiota and its potential as a source of candidate probiotics. It also revisits the interaction between probiotics and host immunity to provide the foundation of the immunomodulatory functions of host-derived probiotics. Several studies demonstrating the immunomodulatory capabilities of host-derived candidate probiotics are given to establish the current knowledge and provide avenues for future research and development in this thematic area of probiotics research in aquaculture.

Modelling Growth and Bacteriocin Production by Lactobacillus plantarum BC-25 in Response to Temperature and pH in Batch Fermentation

The use of bacteriocin-producing probiotics to improve food fermentation processes seems promising. However, lack of fundamental information about their functionality and specific characteristics may hinder their industrial use. Predictive microbiology may help to solve this problem by simulating the kinetics of bacteriocin-producing strains and optimising the cell growth and production of beneficial metabolites. In this study, a combined model was developed which could estimate, from a given initial condition of temperature and pH, the growth and bacteriocin production of Lactobacillus plantarum BC-25 in MRS broth. A logistic model was used to model the growth of cells, and the Luedeking-Piret model was used to simulate the biomass and bacteriocin production. The parameters generated from these primary models were used in a response surface model to describe the combined influence on cell growth, biomass and bacteriocin production. Both the temperature and pH influenced cell and bacteriocin production significantly. The optimal temperature and pH for cell growth is 35 °C and 6.8, and the optimal bacteriocin production condition is a range dependent on two growth-associated constants (YA/X and K), where temperature is from 27 to 34 °C, and pH is 6.35 to 6.65. The developed model is consistent with similar studies and could be a useful tool to control and increase the production of lactic acid bacteria in bioreactors.

Change in cell surface properties of Lactobacillus casei under heat shock treatment

We undertake this study in the aim to give new insight about the change in cellular physiological state under heat shock treatment and probiotic strain screening procedure. Different cell properties have been studied like adhesive ability to biotic and abiotic surfaces, the cell surface hydrophobicity and the fatty acids profiles. Compared to the normal cells, the heated cells increased their adhesive ability to biotic surface. However, the adhesion to abiotic surface was decreased. The cell surface hydrophobicity of the heated strains showed a significant decrease (P < 0.05). Our data revealed that high temperature change the fatty acids profiles of the treated cells, especially the proportions of unsaturated and saturated fatty acid. In fact, the ratio of saturated to unsaturated fatty acids of the heated Lactobacillus casei cells was significantly higher than that of the control cells (P < 0.05). The present finding could firstly add new insight about the response of probiotic to stressful conditions, such us the important role of cell membrane, considered as the first main structure to be damaged by physicochemical stress, in stress resistance because of their composition that can change in adaptation to harsh conditions. Secondly, there is no relationship between changes in membrane composition and fluidity induced by heat shock treatment and adhesion to biotic and abiotic surface.

Leuconostoc citreumMB1 as biocontrol agent ofListeria monocytogenesin milk

Cell-free supernatant fromLeuconostoc citreumMB1 revealed specific antilisterial activity. Preliminary studies demonstrated the proteinaceous, heat-stable, bacteriocin-like trait of the antimicrobial components present in the supernatant. Determination of the genes encoding bacteriocins by PCR and DNA sequencing led to amplification products highly homologous with leucocin A (found in diverseLeuconostocspecies) and UviB (found inLeuc. citreumKM20) sequences. Additionally, antimicrobial activity of cell-free supernatant fromLeuc. citreumMB1 was revealed by an inhibition halo of the SDS-PAGE gel subjected to a direct detection usingListeria monocytogenesas indicator strain. Different assays were carried out to assess the capacity ofLeuc.citreumMB1 to controlList. monocytogenesgrowth: (i) inactivation kinetics of the pathogen by antilisterial compounds present in concentrated cell-free supernatant fromLeuc. citreumMB1, (ii) evaluation of optimalLeuc. citreumMB1 initial concentration to obtain maximumList. monocytogenesATCC 15313 inhibition, and (iii) biocontrol ofList. monocytogenesATCC 15313 withLeuc. citreumMB1 during growth in milk at refrigeration temperature. According to our results, it is unquestionable that at least one bacteriocin is active inLeuc. citreumMB1, since important antilisterial activity was verified either in its cell-free supernatant or in co-culture experiments. Co-culture tests showed that ∼107 CFU/mlLeuc. citreumMB1 was the optimal initial concentration to obtain maximum pathogen inhibition. Moreover,Leuc. citreumMB1 was able to delayList. monocytogenesgrowth at refrigerated temperature.

Physicochemical factors differentially affect the biomass and bacteriocin production by bovine Enterococcus mundtii CRL1656

Bovine Enterococcus mundtii CRL1656 (Centro de Referencia para Lactobacilos Culture Collection) produces an anti-Listeria and anti-Streptococcus dysgalactiae bacteriocin identified as mundticin CRL1656. The strain and its bacteriocin are candidates to be included in a beneficial product to prevent bovine mastitis as an alternative to antimicrobial agents. To optimize the production of biomass and mundticin CRL1656 by E. mundtii CRL1656, a complete 3 × 2(4) factorial design was applied. The effect of culture medium, initial pH, inoculum size, incubation temperature, and agitation conditions on biomass and bacteriocin production was evaluated simultaneously. Growth parameters were determined using the modified Gompertz model. A nonlinear model was used to estimate the effects of the variables on growth parameters. Bacteriocin production was analyzed using a linear mixed model. Optimal biomass and mundticin CRL1656 production by E. mundtii CRL1656 were obtained in different conditions. Maximal growth was recorded in autolyzed yeast, peptone, tryptone, Tween 80, and glucose or M17 broths, pH 6.5, 5.0% inoculum, 30 °C, with agitation. However, bacteriocin titers were higher in autolyzed yeast, peptone, tryptone, Tween 80, and glucose or de Man-Rogosa-Sharpe (MRS) broths, pH 6.5, 30°C, both with or without agitation. Knowledge of the optimum conditions for growth and bacteriocin production of E. mundtii CRL1656 will allow the obtainment of high levels of biomass and mundticin CRL1656 as bioingredients of potential products to prevent bovine mastitis.

Effect of exogenous factors on bacteriocin production from Lactobacillus paracasei J23 by using a resting cell system

A resting cell system was developed for bacteriocin Lac-B23 production from Lactobacillus paracasei J23. The resting cell medium contained (g/L): Glucose 20, Sodium acetate 5.0, MnSO₄ 0.25 MgSO₄ 0.5, Ammoniumhydrogencitrate 1.0, KH₂PO₄ 1.0. The resting cell incubation time and temperature were 20 h and 37 °C and the effects of exogenous factors, including amino acids, glycerol, pyruvic acid, and α-ketoglutaric acid were investigated. Cys and Gly could stimulate the production of bacteriocin, while no stimulus effect was observed for Glu, Tyr and Ala. Glycerol and pyruvic acid increased bacteriocin production and the optimum concentrations were 1% and 30 g/L, respectively. Bacteriocin could act as an inducer of its own biosynthesis. These findings are of importance for the further study of bacteriocin biosynthesis regulation and for the improvement of bacteriocin production yields.

Enterococcus faecium isolated from Lombo, a Portuguese traditional meat product: characterisation of antibacterial compounds and factors affecting bacteriocin production

Strain ST211CH, identified as a strain of Enterococcus faecium, isolated from Lombo produced a bacteriocin that inhibited the growth of Enterococcus spp., Listeria spp., Klebsiella spp., Lactobacillus spp., Pseudomonas spp., Staphylococcus spp. and Streptococcus spp. The mode of action of the bacteriocin named as bacteriocin ST211Ch was bactericidal against Enterococcus faecalis ATCC19443. As determined by Tricine-SDS-PAGE, the approximate molecular mass of the bacteriocin was 8.0 kDa. Loss in antimicrobial activity was recorded after treatment with proteolytic enzymes. Maximum activity of bacteriocin ST211Ch was measured in broth cultures of E. faecium strain ST211Ch after 24 h; thereafter, the activity was reduced. Bacteriocin ST211Ch remained active after exposure to various temperatures and pHs, as well as to Triton X-100, Tween-80, Tween-20, sodium dodecyl sulfate, NaCl, urea and EDTA. Effect of media components on production of bacteriocin ST211Ch was also studied. On the basis of PCR reactions targeting different bacteriocin genes, i.e. enterocins, curvacins and sakacins, no evidences for the presence of these genes in the total DNA of E. faecium strain ST211Ch was obtained. The bacterium most probably produced a bacteriocin different from those mentioned above. Based on the antimicrobial spectrum, stability and mode of action of bacteriocin ST211CH, E. faecium strain ST211Ch might be considered as a potential candidate with beneficial properties for use in biopreservation to control food spoilage bacteria.

Lantibiotics biosynthesis genes and bacteriocinogenic activity of Lactobacillus spp. isolated from raw milk and cheese

Lactobacillus species are usually used as starters for the production of fermented products, and some strains are capable of producing antimicrobial substances, such as bacteriocins. Because these characteristics are highly desirable, research are continually being performed for novel Lactobacillus strains with bacteriocinogenic potential for use by food industries. The aim of this study was to characterise the bacteriocinogenic potential and activity of Lactobacillus isolates. From a lactic acid bacteria culture collection obtained from raw milk and cheese, 27 isolates were identified by 16S rDNA as Lactobacillus spp. and selected for the detection of lantibiotics biosynthesis genes, bacteriocin production, antimicrobial spectra, and ideal incubation conditions for bacteriocin production. Based on the obtained results, 21 isolates presented at least one of the three lantibiotics biosynthesis genes (lanB, lanC or lamM), and 23 isolates also produced antimicrobial substances with sensitivity to at least one proteinase, indicating their bacteriocinogenic activity. In general, the isolates had broad inhibitory activity, mainly against Listeria spp. and Staphylococcus spp. strains, and the best antimicrobial performance of the isolates occurred when they were cultivated at 25 °C for 24 or 48 h or at 35 °C for 12 h. The present study identified the bacteriocinogenic potential of Lactobacillus isolates obtained from raw milk and cheese, suggesting their potential use as biopreservatives in foods.

Isolation and partial characterization of a bacteriocin produced by Pediococcus pentosaceus K23-2 isolated from Kimchi

AIMS

Screening and partial characterization of a bacteriocin produced by Pediococcus pentosaceus K23-2 isolated from Kimchi, a traditional Korean fermented vegetable.

METHODS AND RESULTS

A total of 1000 lactic acid bacteria were isolated from various Kimchi samples and screened for the production of bacteriocin. Pediocin K23-2, a bacteriocin produced by the Pediococcus pentosaceus K23-2 strain, showed strong inhibitory activity against Listeria monocytogenes. The bacteriocin activity remained unchanged after 15 min of heat treatment at 121 degrees C or exposure to organic solvents; however, it diminished after treatment with proteolytic enzymes. The bacteriocin was maximally produced at 37 degrees C, when the pH of the culture broth was maintained at 5.0 during the fermentation, although the optimum pH for growth was 7.0. The molecular weight of the bacteriocin was about 5 kDa according to a tricine SDS-PAGE analysis.

CONCLUSIONS

Pediococcus pentosaceus K23-2 isolated from Kimchi produces a bacteriocin, which shares similar characteristics to the Class IIa bacteriocins. The bacteriocin is heat stable and shows wide antimicrobial activity against Gram-positive bacteria, especially L. monocytogenes.

SIGNIFICANCE AND IMPACT OF THE STUDY

Pediocin K23-2 and pediocin K23-2-producing P. pentosaceus K23-2 could potentially be used in the food and feed industries as natural biopreservatives, and for probiotic application to humans or livestock.