Applicability of a bacteriocin-producing Enterococcus faecium as a co-culture in Cheddar cheese manufacture

Bacteriocin-like inhibitory substances production by Enterococcus faecium 135 in co-culture with Ligilactobacillus salivarius and Limosilactobacillus reuteri

The use of lactic acid bacteria (LAB) and probiotic cultures in the breeding of animals such as poultry and swine are quite common. It is known that those strains can produce bacteriocins when grown in pure culture. However, the production of bacteriocin using co-culture of microorganisms has not been much studied so far. The present study contributes with innovation in this area by embracing the production of bacteriocin-like inhibitory substances (BLIS) by a newly isolated strain of Enterococcus faecium 135. Additionally, the co-cultivation of this strain with Ligilactobacillus salivarius and Limosilactobacillus reuteri was also investigated. The antimicrobial activity of the produced BLIS was evaluated against Listeria monocytogenes, Listeria innocua, Salmonella enterica, and Salmonella enterica serovar Typhimurium using two methods: turbidimetric and agar diffusion. In addition, the presence of enterocin genes was also evaluated. The BLIS produced showed a bacteriostatic effect against the bio-indicator strains, and the highest antimicrobial activities expressed by arbitrary units per mL (AU/mL) were obtained against L. monocytogenes in monoculture (12,800 AU/mL), followed by the co-culture of E. faecium with Limosilactobacillus reuteri (400 AU/mL). After concentration with ammonium sulfate, the antimicrobial activity raised to 25,600 AU/mL. Assays to determine the proteinaceous nature of the BLIS showed susceptibility to trypsin and antimicrobial activity until 90 °C. Finally, analysis of the presence of structural genes of enterocins revealed that four enterocin genes were present in E. faecium 135. These results suggest that BLIS produced by E. faecium 135 has potential to be a bacteriocin and, after purification, could potentially be used as an antimicrobial agent in animal breeding.

Evaluation of probiotic characteristics and whole genome analysis of Pediococcus pentosaceus MR001 for use as probiotic bacteria in shrimp aquaculture

The development of non-antibiotic and environmentally friendly agents is a key consideration for health management in shrimp aquaculture. In this study, the probiotic potential in shrimp aquaculture of Pediococcus pentosaceus MR001, isolated from Macrobrachium rosenbergii, was investigated by means of feeding trial and genetic characterization. In the feeding trial, dietary supplementation with P. pentosaceus MR001 significantly increased weight gain and digestive enzyme activity (p < 0.05) in shrimp, Litopenaeus vannamei. The intestinal histology showed that shrimp given the probiotic diet had healthier guts than the control group. Also, the immune gene expression and the survival rate in the treatment group were significantly increased when compared with the control group. The genetic characteristics of P. pentosaceus strain MR001 were explored by performing whole-genome sequencing (WGS) using the HiSeq 2500 platform and PacBio system, revealing the complete circular genome of 1,804,896 bp. We also identified 1789 coding genes and subsequently characterized genes related to the biosynthesis of bacteriocins, stress resistance, and bile tolerance. Our findings suggest that insights in the functional and genetic characteristics of P. pentosaceus strain MR001 could provide opportunities for applications of such strain in shrimp diet supplementation.

Novel bacteriocins produced by Lactobacillus fermentum strains with bacteriostatic effects in milk against selected indicator microorganisms

The aim of this work was to isolate and characterize bacteriocins produced by 2 Lactobacillus fermentum strains isolated from artisanal Mexican Cocido cheese. Fractions (F ≤3 kDa) obtained from cell-free supernatants of Lb. fermentum strains J23 and J32 were further fractionated by reversed-phase HPLC on a C18 column. Antimicrobial activities of F ≤3 kDa and bacteriocin-containing fractions (BCF), obtained from fractionation of F ≤3 kDa against 4 indicator microorganisms, were determined by the disk diffusion method and growth inhibition in milk. Subsequently, isolated BCF were analyzed by reversed-phase HPLC tandem mass spectrometry. Results showed that BCF presented antimicrobial activity against the 4 indicator microorganisms tested. For J23, one of the fractions (F3) presented the highest activity against Escherichia coli and was also inhibitory against Staphylococcus aureus, Listeria innocua, Salmonella Typhimurium, and Salmonella Choleraesuis. Similarly, fractions F3 and F4 produced by J32 presented antimicrobial activity against all indicator microorganisms. Furthermore, generation time and growth rate showed that F3 from J23 presented significantly higher antimicrobial activity against the 4 indicator microorganisms (2 gram-positive and 2 gram-negative) when inoculated in milk compared with F3 from J32. Interestingly, this fraction presented a broader antimicrobial spectrum in milk than nisin (control). Reversed-phase HPLC tandem mass spectrometry analysis revealed the presence of several peptides in BCF; however, F3 from J23 that was the most active fraction of all presented only 1 bacteriocin. The chemical characterization of this bacteriocin suggested that it was a novel peptide with 10 hydrophobic AA residues in its sequence and a molecular weight of 2,056 Da. This bacteriocin and its producing strain, J23, may find application as a biopreservative against these indicator microorganisms in dairy products.

Influence of different storage conditions on the occurrence of Enterococci in smear ripened cheeses

The number of enterococci was monitored in smear-ripened cheeses stored under different temperature regimes. Sampling and subsequent analyses were performed on the day of manufacture (A/0 = B/0 = C/0), at the end of BBD (A/35, B/35, C/35), two weeks after BBD (A/49, B/49), and eight weeks after BBD (C/91). No statistical difference (p >0.05) was found in the numbers of enterococci in cheeses stored under different temperature regimes until the Best-Before date or at the end of monitoring after 49 and 91 days respectively. At the beginning of storage (A/0, B/0, C/0), the numbers of enterococci in cheeses were 2.3 log CFU.g-1. The highest number of enterococci was recorded after 49 days of storage at 6 °C at 5.4 log CFU.g-1. During storage, there was an increase (p <0.05) in the numbers of enterococci in all types of temperature regimes. Enterococci content was influenced (p <0.05) by both the storage period and storage method (temperature regime).

Ocins for Food Safety

The food industry produces highly perishable products. Food spoilage represents a severe problem for food manufacturers. Therefore, it is important to identify effective preservation solutions to prevent food spoilage. Ocins (e.g., bacteriocins, lactocins, and enterocins) are antibacterial proteins synthesized by bacteria that destroy or suppress the growth of related or unrelated bacterial strains. Ocins represent a promising strategy for food preservation, because of their antagonist effects toward food spoilage microorganisms, high potency, and low toxicity. Additionally, they can be bioengineered. The most common and commercially available ocins are nisin, plantaracin, sakacin P, and pediocin. Several ocins have been characterized and studied biochemically and genetically; however, their structure-function relationship, biosynthesis, and mechanism of action are not understood. This narrative review focuses primarily on ocins and their relevance to the food industry to help prevent food spoilage. In particular, the applications and limitations of ocins in the food industry are highlighted.

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.

Recent advances and industrial viewpoint for biological treatment of wastewaters by oleaginous microorganisms

Recently, technology of using oleaginous microorganisms for biological treatment of wastewaters has become one hot topic in biochemical and environmental engineering for its advantages such as easy for operation in basic bioreactor, having potential to produce valuable bio-products, efficient wastewaters treatment in short period, etc. To promote its industrialization, this article provides some comprehensive analysis of this technology such as its advances, issues, and outlook especially from industrial viewpoint. In detail, the types of wastewaters can be treated and the kinds of oleaginous microorganisms used for biological treatment are introduced, the potential of industrial application and issues (relatively low COD removal, low lipid yield, cost of operation, and lack of scale up application) of this technology are presented, and some critical outlook mainly on co-culture method, combination with other treatments, process controlling and adjusting are discussed systematically. By this article, some important information to develop this technology can be obtained.

Enhanced Control of Listeria monocytogenes by Enterococcus faecium KE82, a Multiple Enterocin-Producing Strain, in Different Milk Environments

Enterococcus faecium KE82, isolated from traditional Greek Graviera cheese, was identified in pure broth cultures in vitro as a multiple enterocin-producing bacterial strain possessing the structural entA, entB, and entP enterocin genes. E. faecium KE82 was further assessed for in situ antilisterial activity in raw milk (RM) and commercially thermized milk (TM; 63°C for 30 s) in the presence of the indigenous microbiota and in sterile raw milk (SRM; 121°C for 5 min) with or without the addition of two commercial starter culture (CSC) strains Streptococcus thermophilus and Lactococcus lactis . Growth of Listeria monocytogenes was completely inhibited in RM incubated at 37°C for 6 h, whereas the pathogen was significantly inactivated in RM+KE82 samples during further incubation at 18°C for 66 h. In contrast, L. monocytogenes levels increased by approximately 2 log CFU/ml in TM, but in TM+KE82 samples, pathogen growth was retarded during the first 6 h at 37°C followed by growth cessation and partial inactivation at 18°C. After 48 to 72 h, growth of L. monocytogenes in SRM+CSC samples decreased by 4 to 5 log CFU/ml compared with the SRM control, whereas additional 10-fold decreases in the pathogen were observed in SRM+CSC+KE82 samples. Reverse transcription PCR analysis of SRM+KE82 and SRM+CSC+KE82 samples confirmed that the entA and entB genes were transcribed, but entP gene transcription was not detected. All RM and SRM samples inoculated with E. faecium KE82 displayed strong in situ inhibitory activity against L. monocytogenes in well diffusion bioassays, whereas activity was weaker to undetectable in comparable or additional TM+KE82 samples; no milk sample without E. faecium KE82 had activity against L. monocytogenes . The findings of this study indicate that E. faecium KE82 is an antilisterial agent that could be used in traditional dairy foods because it concomitantly produces enterocins A and B in situ in milk.

Biological potency and characterization of antibacterial substances produced by Lactobacillus pentosus isolated from Hentak, a fermented fish product of North-East India

Lactic acid bacteria (LAB) isolated from various foods are important due to their potential to inhibit microorganisms, including drug-resistant bacteria. The objectives of this investigation were to isolate and identify antibacterial substances producing LAB from Hentak, a traditional fermented fish product of Manipur (North-East India), and to optimize the production of antagonistic substances present in cell free neutralized supernatant (CFNS) against enteric bacterial pathogens using the ‘one factor at a time’ (OFAT) method. Out of 10 LAB, the most potent bacterium producing antibacterial substances was isolated and identified as Lactobacillus pentosus strain LAP1 based upon morphological, biochemical and molecular characterization. MRS (de Man, Ragosa and Sharpe) medium was determined to provide better bactericidal activity (AU/ml) than other tested media against the indicator enteric bacteria, including Staphylococcus epidermidis MTTC 3615, Micrococcus luteus MTCC 106, Shigella flexneri MTCC 1457, Yersinia enterocolitica MTCC 840 and Proteus vulgaris MTCC 1771. The culture conditions (pH: 5, temperature: 30 °C and inoculum volume: 1 %) and medium components (carbon source: lactose and nitrogen source: ammonium chloride) were observed to be the most influential parameters of significant antagonistic activity of CFNS against the enteric pathogens. MRS medium supplemented with Tween20 effectively stimulated the yield of antibacterial substances. The CFNS of strain LAP1 exhibited sensitivity to proteolytic enzyme (pepsin) treatment and heat treatment (60 °C for 60 min, 100 °C for 30 min and 121 °C for 15 min) and lost its inhibitory properties. The CFNS was active at an acidic (pH 3.0) to neutral pH (pH 7.0) but lost its antagonistic properties at an alkaline pH. The CFNS obtained from strain LAP1 scavenges the DPPH (1,1-diphenyl-2 picrylhydrazyl) significantly in a concentration-dependent manner within the range of 8.8 ± 0.12–57.35 ± 0.1 %. The OFAT-based approach revealed the baseline for statistical optimization, the scale-up process and efficient production of CFNS by L. pentosus strain LAP1, which could be used as a potential antibacterial and free radical scavenging agent.

Behaviour of Listeria Monocytogenes in Artisanal Raw Milk Pecorino Umbro Cheese: A Microbiological Challenge Test

In the present study, a microbiological challenge test in artificially contaminated raw milk Pecorino Umbro cheese during cheese-making was carried out. Raw ewe milk was contaminated by a suspension of particular Listeria monocytogenes strains. The number of L. monocytogenes and L. monocytogenes dynamic growth were evaluated during cheese-making and storage. A significant decrease of the viable count of L. monocytogenes was observed during ripening and L. monocytogenes viable count was below the limit of quantification during storage. The results show that the product is unable to support the growth of the pathogen.

Measurement of pH micro-heterogeneity in natural cheese matrices by fluorescence lifetime imaging

Cheese, a product of microbial fermentation may be defined as a protein matrix entrapping fat, moisture, minerals and solutes as well as dispersed bacterial colonies. The growth and physiology of bacterial cells in these colonies may be influenced by the microenvironment around the colony, or alternatively the cells within the colony may modify the microenvironment (e.g., pH, redox potential) due to their metabolic activity. While cheese pH may be measured at macro level there remains a significant knowledge gap relating to the degree of micro-heterogeneity of pH within the cheese matrix and its relationship with microbial, enzymatic and physiochemical parameters and ultimately with cheese quality, consistency and ripening patterns. The pH of cheese samples was monitored both at macroscopic scale and at microscopic scale, using a non-destructive microscopic technique employing C-SNARF-4 and Oregon Green 488 fluorescent probes. The objectives of this work were to evaluate the suitability of these dyes for microscale pH measurements in natural cheese matrices and to enhance the sensitivity and extend the useful pH range of these probes using fluorescence lifetime imaging (FLIM). In particular, fluorescence lifetime of Oregon Green 488 proved to be sensitive probe to map pH micro heterogeneity within cheese matrices. Good agreement was observed between macroscopic scale pH measurement by FLIM and by traditional pH methods, but in addition considerable localized microheterogeneity in pH was evident within the curd matrix with pH range between 4.0 and 5.5. This technique provides significant potential to further investigate the relationship between cheese matrix physico-chemistry and bacterial metabolism during cheese manufacture and ripening.

Inhibitory activity of Lactobacillus plantarum TF711 against Clostridium sporogenes when used as adjunct culture in cheese manufacture

Bacteriocins produced by lactic acid bacteria are of great interest to the food-processing industry as natural preservatives. This work aimed to investigate the efficacy of bacteriocin-producing Lactobacillus plantarum TF711, isolated from artisanal Tenerife cheese, in controlling Clostridium sporogenes during cheese ripening. Cheeses were made from pasteurised milk artificially contaminated with 10(4) spores m/l C. sporogenes. Experimental cheeses were manufactured with Lb. plantarum TF711 added at 1% as adjunct to commercial starter culture. Cheeses made under the same conditions but without Lb. plantarum TF711 served as controls. Evolution of microbiological parameters, pH and NaCl content, as well as bacteriocin production was studied throughout 45 d of ripening. Addition of Lb. plantarum TF711 did not bring about any significant change in starter culture counts, NaCl content and pH, compared with control cheese. In contrast, clostridial spore count in experimental cheeses were significantly lower than in control cheeses from 7 d onwards, reaching a maximum reduction of 2·2 log units on day 21. Inhibition of clostridia found in experimental cheeses was mainly attributed to plantaricin activity, which in fact was recovered from these cheeses.

Enterocin HZ produced by a wild Enterococcus faecium strain isolated from a traditional, starter-free pickled cheese

Bacteriogenic Enterococcus faecium HZ was identified by using biochemical (Strep-API 20, API-50 CHL, fatty acid profile) and 16S rRNA analysis (99·99 %). Ent. faecium HZ was sensitive to clinically important antibiotics such as vancomycin, and did not have gelatinase and haemolysis activities. Enterocin HZ, a bacteriocin from Ent. faecium HZ, was sensitive to papain and tyripsin, but resistant to pepsin, lipase, catalase, α-amylase, organic solvents, detergents, ß-mercaptoethanol, and heat treatment (90 °C/30 min). It was biologically active at pH 2·0-9·0 and synthesised at the highest level in MRS or M17 broth at 32 or 37 °C with an inoculum amount of 0·1-0·5 % and an initial pH of 6·0-7·0. Enterocin HZ production reached maximum level at middle and late logarithmic phase and its molecular weight was ∼4·5 kDa. It was active against some Gram-positive foodborne bacteria. Ent. faecium HZ or its bacteriocin enterocin HZ is a good candidate to be studied as a food biopreservative since enterocin HZ showed strong bactericidal activity against Listeria monocytogenes in UHT milk and also Ent. faecium HZ grew very well in milk and produced enterocin HZ at maximum level.

Optimization of bacteriocin production by Lactobacillus sp. MSU3IR against shrimp bacterial pathogens

BACKGROUND

Aquaculture is one amongst the growing and major food producing sectors. Shrimp culture is one of the subsectors of aquaculture that attracts more attention because of the economic interest. However, the shrimp culture systems have been facing severe consequences and economical losses due to disease outbreaks. Risk of disease outbreak can be combated with the application of probiotics. For economically viable production of such probiotic products, the present study provides information on the optimization and partial purification of bacteriocin produced by a goat milk isolate Lactobacillus sp. MSU3IR against the shrimp bacterial pathogens.

RESULTS

Bacteriocin production was estimated as a measure of bactericidal activity (arbitrary Unit/ml) over the test strains. The optimum culture conditions and media components for maximum bacteriocin production by Lactobacillus sp. MSU3IR were: pH: 5.0, temperature: 30°C, carbon source: lactose; nitrogen source: ammonium acetate; NaCl: 3.0% and surfactant: Tween 80. MRS medium was found to extend better bacteriocin production than other tested media. Upon partial purification of bacteriocin, the SDS-PAGE analysis had manifested the presence of two peptide bands with the molecular weight of 39.26 and 6.38 kDa, respectively.

CONCLUSION

The present results provide baseline trend for the statistical optimization, scale up process and efficient production of bacteriocin by the candidate bacterial strain Lactobacillus sp. MSU3IR which could be used to replace the usage of conventional chemotherapeutics in shrimp culture systems.

Technological properties and probiotic potential of Enterococcus faecium strains isolated from cow milk

AIM

To identify enterococci from the fermentation of milk for the production of nono, an African fermented dairy product, to determine the technological properties for suitability as starter cultures and safety as probiotics.

METHODS AND RESULTS

Enterococcus faecium CM4 and Enterococcus faecium 2CM1 were isolated from raw cow's milk. The strains were phenotypically and genotypically identified. Technological properties, safety investigations, in vitro adherence properties and antimicrobial characteristics were carried out. Strong acidification and tolerance to bile salts were recorded. The strains were bile salts hydrolytic positive and no haemolysis. There was no resistance to clinically relevant antibiotics. The strains exhibited adherence to human collagen type IV, human fibrinogen and fibronectin. The bacteriocins were active against Bacillus cereus DSM 2301, Bacillus subtilis ATCC 6633, Micrococcus luteus and Listeria monocytogenes. Bacteriocins were stable at pH 4-9 and on treatment with lipase, catalase, α-amylase and pepsin, while their activity was lost on treatment with other proteases. The bacteriocins produced were heat stable at 100°C for 10 min. The bacteriocin produced by the strains was identified as enterocin A.

CONCLUSIONS

The E. faecium strains in this study exhibited probiotic activity, and the safety investigations indicate their suitability as good candidates for a starter culture fermentation process.

SIGNIFICANCE AND IMPACT OF THE STUDY

The use of bacteriocin-producing E. faecium strains as starter cultures in fermented foods is beneficial but, however, their safety investigations as probiotics must be greatly emphasized.

Antimicrobial activity of Enterococcus Faecium Fair-E 198 against gram-positive pathogens

This study investigated the antimicrobial activity of Enterococcus faecium FAIR-E 198 against Bacillus cereus, Listeria monocytogenes and Staphylococcus aureus. Using the critical-dilution method, the bacteriocin produced by E. faecium FAIR-E 198 inhibited all L. monocytogenes strains evaluated (1,600 to 19,200 AU mL(-1)). However, none of the B. cereus and S. aureus strains investigated were inhibited. The maximum activity of this bacteriocin (800 AU mL(-1)) was observed in MRS broth, while the activity in milk was 100 AU mL(-1). In the co-cultivation test in milk, B. cereus K1-B041 was reduced to below the detection limit (1.00 log CFU mL(-1)) after 48 h. E. faecium reduced the initial L. monocytogenes Scott A population by 1 log CFU mL(-1) after 3 h at 35°C, However, the pathogen regained growth, reaching 3.68 log CFU mL(-1) after 48 h. E. faecium did not influence the growth of S. aureus ATCC 27154 during the 48 h of co-cultivation, Therefore, it can be concluded that the effectiveness of the antimicrobial activity of E. faecium FAIR-E 198 is strictly related to the species and strain of the target microorganism and to the culture medium.

Functional properties of novel protective lactic acid bacteria and application in raw chicken meat against Listeria monocytogenes and Salmonella enteritidis

In this study 635 lactic acid bacteria of food origin were evaluated for their potential application as protective cultures in foods. A stepwise selection method was used to obtain the most appropriate strains for application as protective cultures in chicken meat. Specifically, all strains were examined for antimicrobial activity against various Gram positive and Gram negative pathogenic and spoilage bacteria. Strains exhibiting anti-bacterial activity were subsequently examined for survival in simulated food processing and gastrointestinal tract conditions, such as high temperatures, low pH, starvation and the presence of NaCl and bile salts. Selected strains where then examined for basic safety properties such as antibiotic resistance and haemolytic potential, while their antimicrobial activity was further investigated by PCR screening for possession of known bacteriocin genes. Two chosen strains were then applied on raw chicken meat to evaluate their protective ability against two common food pathogens, Listeria monocytogenes and Salmonella enteritidis, but also to identify potential spoilage effects by the application of the protective cultures on the food matrix. Antimicrobial activity in vitro was evident against Gram positive indicators, mainly Listeria and Brochothrix spp., while no antibacterial activity was obtained against any of the Gram negative bacteria tested. The antimicrobial activity was of a proteinaceous nature while strains with anti-listerial activity were found to possess one or more bacteriocin genes, mainly enterocins. Strains generally exhibited sensitivity to pH 2.0, but good survival at 45 degrees C, in the presence of bile salts and NaCl as well as during starvation, while variable survival rates were obtained at 55 degrees C. None of the strains was found to be haemolytic while variable antibiotic resistance profiles were obtained. Finally, when the selected strains Enterococcus faecium PCD71 and Lactobacillus fermentum ACA-DC179 were applied as protective cultures in chicken meat against L. monocytogenes and S. enteritidis respectively, a significantly reduced growth of these pathogenic bacteria was observed. In addition, these two strains did not appear to have any detrimental effect on biochemical parameters related to spoilage of the chicken meat.

The role of environmental factors and medium composition on bacteriocin-like inhibitory substances (BLIS) production by Enterococcus mundtii strains

Bacteriocin-like inhibitory substances (BLIS)-producers Enterococcus mundtii WGWT1-1A, WGW11.2, WGJ20.1, WGJ40.2 and WGK53 from raw material origin were subjected to a study for the characterization of antimicrobial compound production under several growth conditions, including different cultivation media, growth temperatures, pHs, different concentrations and sources of nitrogen compounds, carbohydrates and other nutritional factors, and in the presence of different percentages of ethanol and NaCl. The five E. mundtii strains showed different behaviors. However, in all cases, MRS and sour dough bacteria (SDB) were found as the optimal media for BLIS production. In general, the higher BLIS production was observed with pH in the range 6.0-8.0 and, except 45 degrees C, the temperature did not show a defining effect. Low or no BLIS activity was detected after growth without nitrogen sources and carbohydrates. Absence of Tween 80, triammoniun citrate, K2HPO4, MgSO4 and MnSO4 did not affect BLIS activity levels. Except for a strain (WGWT1-1A), ethanol did not play a negative role in BLIS expression, while NaCl determined decrease of BLIS activity, proportional with concentration. The above strains did not contain plasmids, hence, BLIS expression is encoded by chromosomal DNA.

Isolation and characterization of a new bacteriocin, termed enterocin M, produced by environmental isolate Enterococcus faecium AL41

The new bacteriocin, termed enterocin M, produced by Enterococcus faecium AL 41 showed a wide spectrum of inhibitory activity against the indicator organisms from different sources. It was purified by (NH4)2SO4 precipitation, cation-exchange chromatography and reverse phase chromatography (FPLC). The purified peptide was sequenced by N-terminal amino acid Edman degradation and a mass spectrometry analysis was performed. By combining the data obtained from amino acid sequence (39 N-terminal amino acid residues was determined) and the molecular weight (determined to be 4628 Da) it was concluded that the purified enterocin M is a new bacteriocin, which is very similar to enterocin P. However, its molecular weight is different from enterocin P (4701.25). Of the first 39 N-terminal residues of enterocin M, valine was found in position 20 and a lysine in position 35, while enterocin P has tryptophane residues in these positions.

Influence of peroxyacetic acid and nisin and coculture with Enterococcus faecium on Listeria monocytogenes biofilm formation

Biofilm formation is a matter of concern in food industries because biofilms facilitate the survival of pathogenic bacteria such as Listeria monocytogenes, which may contaminate food-processing equipment and products. In this study, nisin and two Enterococcus faecium strains were evaluated for their effect on biofilm formation by L. monocytogenes cultured in brain heart infusion broth and on stainless steel coupons. Elimination of preformed L. monocytogenes biofilms by peroxyacetic acid also was tested. Adhesion control experiments were performed with pure cultures of L. monocytogenes after swab collection of adhered cells, which were then enumerated on PALCAM agar plates and visualized by scanning electron microscopy. Formation of a biofilm was recorded when the number of adhered cells was at least 10(3) CFU/cm2. When L. monocytogenes was cocultured with E. faecium bac-, the number of adhered L. monocytogenes cells was 2.5 log lower (P = 0.002) when initially compared with the control culture, but after 6 h of incubation a biofilm was again detected. However, in coculture on stainless steel coupons, E. faecium bac+ inhibited L. monocytogenes adherence and did not allow biofilm formation for up to 48 h (P < 0.001). In the presence of nisin or after treatment with peroxyacetic acid, bacterial growth was reduced (P < 0.001) up to 4.6 and 5.6 log CFU/cm2, respectively, when compared with L. monocytogenes cultures on untreated coupons. However, after these treatments, cells were still present, and after 24 h of incubation, a renewed biofilm was detected in L. monocytogenes cultures treated with nisin. Although all tested conditions reduced L. monocytogenes growth to some extent, only coculture with E. faecium bac+ efficiently reduced biofilm formation, suggesting a potential control strategy for this pathogen.

Bacteriocins from lactic acid bacteria: production, purification, and food applications

In fermented foods, lactic acid bacteria (LAB) display numerous antimicrobial activities. This is mainly due to the production of organic acids, but also of other compounds, such as bacteriocins and antifungal peptides. Several bacteriocins with industrial potential have been purified and characterized. The kinetics of bacteriocin production by LAB in relation to process factors have been studied in detail through mathematical modeling and positive predictive microbiology. Application of bacteriocin-producing starter cultures in sourdough (to increase competitiveness), in fermented sausage (anti-listerial effect), and in cheese (anti-listerial and anti-clostridial effects), have been studied during in vitro laboratory fermentations as well as on pilot-scale level. The highly promising results of these studies underline the important role that functional, bacteriocinogenic LAB strains may play in the food industry as starter cultures, co-cultures, or bioprotective cultures, to improve food quality and safety. In addition, antimicrobial production by probiotic LAB might play a role during in vivo interactions occurring in the human gastrointestinal tract, hence contributing to gut health.

A food-grade system for production of pediocin PA-1 in nisin-producing and non-nisin-producing Lactococcus lactis strains: application to inhibit Listeria growth in a cheese model system

Food-grade heterologous production of pediocin PA-1 in nisin-producing and non-nisin-producing Lactococcus lactis strains, previously selected because of their technological properties for cheese making, was achieved. Plasmid pGA1, which contains the complete pediocin operon under the control of the strong P32 promoter and is devoid of any antibiotic marker, was introduced into L. lactis ESI 153 and L. lactis ESI 515 (Nis+). Transformation of L. lactis ESI 515 with pGA1 did not affect its ability to produce nisin. The antimicrobial activity of the pediocin-producing transformants on the survival of Listeria innocua SA1 during cheese ripening was also investigated. Cheeses were manufactured from milk inoculated with 1% of the lactic culture and with or without approximately 4 log CFU/ml of the Listeria strain. L. lactis ESI 153, L. lactis ESI 515, and their transformants (L. lactis GA1 and GA2, respectively) were used as starter cultures. At the end of the ripening period, counts of L. innocua in cheeses made with the bacteriocin-producing lactococcal strains were below 50 CFU/g in the L. lactis GA1 cheeses and below 25 CFU/g in the L. lactis GA2 ones, compared with 3.7 million CFU/g for the controls without nisin or pediocin production.

Screening of lactic acid bacteria for bacteriocins by microbiological and PCR methods

We describe a practical laboratory designed for third-year undergraduate students of Biotechnology as part of a Microbial Physiology and Genetics course. It comprises a five-session laboratory module to screen foods for lactic acid bacteria (LAB)1 and to test isolated LAB for the presence of bacteriocins. Traditional Thai fermented foods are first screened for bacteriocin-producing LAB using microbiological methods. This is followed by a simple and rapid DNA extraction and by a multiplex polymerase chain reaction (PCR) using three pairs of specific primers to test for the presence or absence of various bacteriocin genes in the isolated LAB. PCR amplicons of 332, 412, and 608 bp indicate the presence of pediocin, enterocin, and nisin genes, respectively, whereas no amplicon band indicates the absence of these bacteriocins. The laboratory provides the students with experience in the use of microbiological and multiplex PCR methods and shows how the molecular biology techniques can be related to their daily lives. The module could easily be adapted to the study of fermented foods from other countries.