High-salt brines compromise autoinducer-mediated bacteriocinogenic Lactobacillus plantarum survival in Spanish-style green olive fermentations

The effect of NaCl on plantaricin production by five Lactobacillus plantarum strains was investigated. Plantaricin production in these strains was found to be regulated by three-component regulatory systems ruled by two different autoinducer peptides (AIPs), either PLNC8IF or Plantaricin A. Bacteriocin activity exhibited by these strains came to a halt in liquid medium containing NaCl concentrations of or above 2%. In contrast, bacteriocin activity was still observed when the producing strains were growing on solid medium containing up to 4% NaCl. Bacteriocin activity in liquid medium containing up to 2% NaCl could be restored by coculturing the producing strains with a selected plantaricin-production inducing strain of Lactococcus lactis. Growth of these bacteriocinogenic L. plantarum strains was monitored in traditional Spanish-style green olive fermentations. Survival of these strains could not be enhanced when provided with a range of plantaricin-production inducing mechanisms previously described, such as constitutive AIP production or coinoculation with a specific bacteriocin-production inducing strain of L. lactis. Our results suggest that it is advisable the use of constitutive bacteriocin producers, or at least non-AIP-dependant ones, as starters for olive fermentations due to the intrinsic physical characteristics of this food fermentation, especially the high salt concentration of the brines currently used.     

Coculture with specific bacteria enhances survival of Lactobacillus plantarum NC8, an autoinducer-regulated bacteriocin producer,in olive fermentations

Bacteriocin production in Lactobacillus plantarum NC8 is activated by coculture with specific bacteriocin production-inducing bacterial strains. The system is further regulated by a three-component regulatory system involving a specific autoinducer peptide (PLNC8IF). We have used L. plantarum NC8 as a starter culture in Spanish-style green olive fermentations and examined the influence of coculturing in its survival. We found that L. plantarum NC8 greatly enhanced its growth and survival in the olive fermentations when coinoculated with two specific bacteriocin-production inducing strains, i.e. Enterococcus faecium 6T1a-20 and Pediococcus pentosaceus FBB63, when compared to singly-inoculated fermentations. In addition, a constitutive bacteriocin-producer NC8-derivative strain was used as a control in the olive fermentations and showed also better viability than the parental NC8 strain. Our results suggest the involvement of bacteriocin production in the viability enhancement found in both cases. We postulate that the presence of specific bacteria is recognized by L. plantarum NC8 as an environmental stimulus to switch a specific adaptive response on, most probably involving bacteriocin production. The design of novel bacteriocin-producing starter cultures for food fermentations should consider their constitutive versus regulated character.     

Biochemical,antimicrobial and molecular characterization of a noncytotoxic bacteriocin produced by Lactobacillus plantarum ST71KS

Lactobacillus (Lb.) plantarum ST71KS was isolated from homemade goat feta cheese and identified using biochemical and molecular biology techniques. As shown by Tricine-SDS-PAGE, this lactic acid bacterium produces a bacteriocin (ST71KS) with an estimated molecular weight of 5.0 kDa. Bacteriocin ST71KS was not affected by the presence of α-amylase, catalase and remained stable in a wide range of pH and after treatment with Triton X-100, Triton X-114, Tween 20, Tween 80, NaCl, SDS, urea and EDTA. This bacteriocin also remained active after being heated at 100 °C for 2 h and even after 20 min at 121 °C; however, it was inactivated by proteolitic enzymes. Production of bacteriocin ST71KS reached 6400 AU/mL during stationary growth phase of Lb. plantarum cultivated in MRS at 30 °C and 37 °C. Bacteriocin ST71KS displayed a bactericidal effect against Listeria monocytogenes strains 603 and 607 and did not adsorb to the producer cells. Lb. plantarum ST71KS harbors two bacteriocin genes with homology to plantaricin S and pediocin PA-1. These characteristics indicate that bacteriocin ST71KS is a class IIa bacteriocin. The peptide presented no toxic effect when tested in vitro with kidney Vero cells, indicating safe technological application to control L. monocytogenes in foods.     

Probiotic potential of Lactobacillus strains with anti-allergic effects from kimchi for yogurt starters

Lactobacillus strains were isolated from kimchi and investigated for their potential use for probiotic yogurt starters. Two of the isolated strains have over 90% survival rate to artificial gastric acid (pH 2.5, 1% pepsin) and artificial bile acid (0.3% oxgall). These strains were identified as Lactobacillus plantarum by 16S rRNA sequencing, and named as L. plantarum SY11 and L. plantarum SY12. The known carcinogenic enzyme, β-glucuronidase was not produced by L. plantarum SY11 and L. plantarum SY12. These 2 strains were found to be resistant to several antibiotics and strongly adhered to intestinal cells. Antiallergic effect of L. plantarum SY11 and L. plantarum SY12 was demonstrated using nitric oxide (NO) and cytokine production. L. plantarum SY11 and L. plantarum SY12 were capable of significantly decreasing NO production, and reduced T helper 2-associated cytokines, cyclooxygenase-2, tumor necrosis factor-α, and inducible nitric oxide synthase compared to control. Yogurt samples produced using L. plantarum SY11 and L. plantarum SY12 did not show significant differences in microbiological, physicochemical, and sensory properties compared with yogurt sample produced using commercial strain. Therefore, these two strains could be used as probiotic yogurt starters with antiallergic effects.     

Bacteriocinogenic Lactobacillus plantarum ST16Pa isolated from papaya (Carica papaya) — From isolation to application: Characterization of a bacteriocin

Strain ST16PA, isolated from papaya was identified as Lactobacillus plantarum based on biochemical tests, PCR with species-specific primers and 16S rDNA sequencing. L. plantarum ST16PA produces a 6.5 kDa bacteriocin, active against different species from genera Enterobacter, Enterococcus, Lactobacillus, Pseudomonas, Streptococcus and Staphylococcus and different serotypes of Listeria spp. The peptide is inactivated by proteolytic enzymes, but not when treated with ??-amylase, catalase, lipase, Triton X-100, SDS, Tween 20, Tween 80, urea, NaCl and EDTA. However, presence of 1% Triton X-114 deactivates the bacteriocin. No change in activity was recorded after 2 h at pH values between 2.0 and 12.0, and after treatment at 100 °C for 120 min or 121 °C for 20 min. The mode of activity against Lactobacillus sakei ATCC 15521, Enterococcus faecalis ATCC 19443 and Listeria innocua 2030C was bactericidal, resulting in cell lysis and enzyme-leakage. No significant differences in cell growth and bacteriocin production were observed when strain ST16Pa was cultured in MRS broth at 26 °C and 30 °C for 24 h (25 600 AU/ml). However, even though strain ST16PA grows well in MRS broth at 15 °C and 37 °C, a reduction of bacteriocin production was observed (400 AU/ml and 1600 AU/ml, respectively). In addition, effect of MRS medium components, different initial pH and additions of glycerol or vitamins to the media on bacteriocin ST16Pa production was studied.Peptide ST16PA adsorbs (400 AU/ml) to producer cells. However, bacteriocin ST16Pa was adsorbed at 50% to cells of L. innocua 2030C and at 75% to L. sakei ATCC 15521 and E. faecalis ATCC 19433 when experiments were conducted at 30 °C and pH 6.5. Adsorption of bacteriocin ST16Pa to target cells at different temperatures, pH and in presence of potassium sorbate, sodium nitrate, sodium chloride, ascorbic acid, Tween 80 and Tween 20 were also studied. To the best of our knowledge, this is the first report on detection of L. plantarum in papaya.     

The role of plNC8HK-plnD genes in bacteriocin production in Lactobacillus plantarum KLDS1.0391

The function of plNC8HK gene and plnD gene on the bacteriocin production of Lactobacillus plantarum KLDS1.0391 was studied. The results of bioinformatics analysis showed that PlNC8HK protein was a histidine protein kinase and a cytoplasmic membrane protein with six transmembrane helices. PlnD protein was a response regulator of the LytR/AlgR family. Quantitative real-time PCR revealed that plNC8HK and plnD genes of L. plantarum KLDS1.0391 were up-regulated significantly (P < 0.01) when L. plantarum KLDS1.0391 co-cultured with Lactobacillus helveticus KLDS1.9207. The plNC8HK-plnD mutant was also constructed. The change of antibacterial activity, AI-2 activity and cell number of plNC8HK-plnD mutant in co-culture and mono-culture demonstrated that plNC8HK and plnD genes were essential for bacteriocin production in L. plantarum KLDS1.0391, and the increase of bacteriocin production correlated closely with plNC8HK and plnD genes in co-culture. These results are beneficial to understand the role of two components system in the bacteriocin production of L. plantarum.     

Diversity of Streptococcus thermophilus in bacteriocin production; inhibitory spectrum and occurrence of thermophilin genes

The bacteriocin-producing Streptococcus thermophilus strains that can dominate in natural dairy ecosystems, may also enhance safety in products obtained from natural cultures. In this study, we sought to identify bacteriocin production and bacteriocin genes in 75 strains of dairy and plant origin. The strains were tested for antimicrobial activity against pathogens or pathogen models, spoiling bacteria, and lactic acid bacteria associated with dairy products. All strains moderately inhibited Staphylococcus aureus P310, none inhibited Listeria innocua LMG 11387^T or Clostridium tyrobutyricum LMG 1285^T. In addition, 14 were active against one or more indicators in addition to S. aureus P310. Inhibition of other starter bacteria was more common than the inhibition of unwanted microorganisms. The involvement of a proteinaceous compound was ascertained in all cases. Results suggested that the selection of bacteriocinogenic S. thermophilus strains for use in biopreservation must take into account the effects exerted on other lactic acid bacteria.     

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

This study was conducted to investigate the effect of cultural conditions and nutritional components on the cell growth and bacteriocin production of Lactobacillus plantarum KC21. In cultures without pH control, the bacteriocin activity of L. plantarum KC21 was higher at 30oC, however, the cell growth rate was higher at 37°C. In MRS broth with an initial pH 6.0, the cell growth was lower, but high bacteriocin levels were recorded than at pH 7.0. The bacteriocin activity was maximal in medium containing 1.0 or 1.5% glucose or 1.0% lactose. Yeast extract (0.25 or 0.5%) added to MRS broth increased the bacteriocin activity, moreover, the bacteriocin in the presence of 1.0 or 3.0% NaCl, 0.5% NH₄PO₄, or 0.25 or 0.5% KH₂PO₄ resulted in the activity of 12,800 BU/mL, but excessively high salts concentration hindered the cell growth and bacteriocin production significantly. Besides 1.0 or 2.0 mM MgSO₄ highly increased the bacteriocin activity without affecting the growth of L. plantarum KC21, and ascorbic acid (1.0 or 3.0 ppm) enhanced the bacteriocin activity up to 2 fold.     

Pressure-resistant acclimation of lactic acid bacteria from a natural fermentation product using high pressure

Twenty colonies of Pediococcus acidilactici, Lactobacillus brevis, Lactiplantibacillus plantarum and Latilactobacillus curvatus were isolated from fermentation broth of pickled pepper by using MRS agar. The strains were acclimated using high pressure from 300 to 400 MPa for 1 to 5 min. For one generation of acclimation, the survived cells after first high pressure treatment were then activated by culturing on MRS agar for two days for the next high pressure treatment. After acclimation for 30 generations, the survival ratio of L. plantarum and L. curvatus was increased by 138 and 1222 times at 400 MPa for 1 and 3 min, respectively. Weibull model could appropriately fit the survival curves of L. plantarum and L. curvatus treated by high pressure. The time to the first decimal reduction of these two strains after acclimation was 3.5 and 1.8 times, respectively, longer than before acclimation at 300 MPa. From electron microscopy photographs, the acclimated L. curvatus was more curved, smaller and its cell wall was thicker than the unacclimated L. curvatus. After HPP treatment, L. plantarum and L. curvatus have higher cell integrity, smoother cell surface, more uniform protoplasm and smaller cavities in the cell protoplasm compared with unacclimated strains, suggesting that high pressure acclimation introduced some modification to bacteria intrinsic structures and increased their pressure resistance. Moreover, the fermentation performance including glucose utilization capacity and lactic acid production of the acclimated L. curvatus was respectively improved by 9.6% and 9.4% at 37 °C for 24 h in MRS medium.     

Characterisation of an antiviral pediocin-like bacteriocin produced by Enterococcus faecium

The bacteriocin-producing strain Enterococcus faecium ST5Ha was isolated from smoked salmon and identified by biomolecular techniques. Ent. faecium ST5Ha produces a pediocin-like bacteriocin with activity against several lactic acid bacteria, Listeria spp. and some other human and food pathogens, and remarkably against HSV-1 virus. Bacteriocin ST5Ha was produced at high levels in MRS broth at 30 °C and 37 °C, reaching a maximum production of 1.0 × 10⁹ AU/ml, checked against Listeria ivanovii ATCC19119 as target strain and surrogate of pathogenic strain Listeria monocytogenes. The molecular weight of bacteriocin ST5Ha was estimated to be 4.5 kDa according to tricine-SDS-PAGE data. Ent. faecium ST5Ha harbors a 1.044 kb chromosomal DNA fragment fitting in size to that of pediocin PA-1/AcH. In addition, the sequencing of bacteriocin ST5Ha gene indicated 99% of DNA homology to pediocin PA-1/AcH. The combined application of low levels (below MIC) of ciprofloxacin and bacteriocin ST5Ha resulted in a synergetic effect in the inhibition of target strain L. ivanovii ATCC19119. Bacteriocin ST5Ha displayed antiviral activity against HSV-1, an important human pathogen, with a selectivity index of 173. To the best of our knowledge, this is the first report on Ent. faecium as a potential producer of pediocin-like bacteriocin with antiviral activity.     

Physical properties and antilisterial activity of bioactive edible films containing Lactobacillus plantarum

Bioactive polymeric films were developed from the incorporation of Lactobacillus plantarum into polysaccharide or protein edible films. Lactic acid bacteria (LAB) were added directly to the film forming solution and films were obtained by casting. Four different biopolymers were tested: sodium caseinate, pea protein, methylcellulose and hydroxypropylmethylcellulose. In order to study the impact of the incorporation of the protective culture into the biopolymer matrix, the water vapour permeability (WVP), optical and mechanical properties of the dry films were evaluated. Furthermore, survival of L. plantarum and the antimicrobial potential of bioactive films against Listeria innocua were studied. Whereas optical and mechanical properties of the films were not notably altered by the LAB incorporation, WVP values increased for all biopolymers. Viability of the strain was lower in cellulose derivative matrices than in protein films, although bacteriocin production in the newly prepared films was greater in these matrices. As a result, a significant antimicrobial activity against L. innocua was observed for polysaccharide matrices, which was not observed for protein films, where the bacteriocin production is delayed. In pea protein films the maximum bacteriocin production occurs at 15 storage days and afterwards decreases. So, the nature of the biopolymer and the knowledge of time when an adequate bacteriocin concentration is produced are key to use bioactive films in an effective way.     

Bacteriocin-producing lactobacilli in Spanish-style fermented sausages: characterization of bacteriocins

Three bacteriocins were studied. Sakacin K, a bacteriocin from Lactobacillus sake CTC494 was purified to homogeneity by a four-step system involving ammonium sulphate precipitation, binding to a cation exchanger, hydrophobic interaction and reverse phase chromatography in FPLC (fast performance liquid chromatography) system. The peptide sequence was determined by Edman degradation. The first 30 amino acid residues from the N-terminus of sakacin K were identical to those of curvacin A from Lactobacillus curvatus LTH1174 and sakacin A from Lactobacillus sakei Lb706. The structural gene of sakacin K in Lb. sake CTC494 was located on a 60 Kbp plasmid (as has been previously reported) by curvacin A in Lb. curvatus LTH1174 and sakacin A in Lb. sakei Lb706. Plantaricin D, a bacteriocin-like compound isolated from Lb. plantarum CTC305 was purified and sequenced using the same procedure as described for sakacin K. The first 15 amino acid residues of plantaricin D were identical to those obtained from the bacteriocin inducer peptide (termed plantaricin A) of the bacteriocinogenic system in Lb. plantarum C11. The structural gene of the plantaricin D peptide was located on a similar EcoRl chromosomal fragment when compared to plantaricin A in Lb. plantarum C11. These two isolated bacteriocin-like peptides (sakacin K and plantaricin D) were purified from two new different strains obtained from fermented meat, confirming the ecological importance of these substances. Lactobacillus sakei CTC372, the third bacteriocinogenic strain selected in this study from fermented sausages, produced a bacteriocin named sakacin T. The bacteriocin is not found free in the supernatant of the cells. It is active against Listeria monocytogenes and Staphylococcus aureus. The genetic determinant of this bacteriocin was localized in a 84·4 Kbp plasmid by conjugative transfer and curing assays.     

Isolation and characterization of acid-sensitive Lactobacillus plantarum with application as starter culture for Nham production

The aim of this study was to derive new starter culture variants that are unable to grow below pH 4.6, the desirable pH of the Thai fermented pork sausage, Nham, specified by Thailand Food Standard, and apply them in Nham fermentation. Several acid-sensitive mutants of one of the commercial Nham starter cultures, Lactobacillus plantarum BCC 9546, were isolated as spontaneous neomycin-resistant mutants. The growth of three representative mutants was characterized in MRS broth, which revealed that their cell numbers and acid production were lower than that of the wild-type. The H⁺-ATPase activities of the three mutants were found significantly lower than that of the wild-type under either neutral or acidic conditions. Consequently, internal pH values of the mutants appeared to be lower, especially in acidic environment (pH 5). The most acid-sensitive mutant was applied in experimental Nham production and the pH of Nham fermented with the mutant had significantly higher pH at the end of fermentation (3 days) and after an additional 4 days of storage at 30 °C. These results indicate that the use of acid-sensitive L. plantarum as starter culture can reduce the severity of post-acidification and increase the shelf life of Nham at ambient temperature.     

Degradation of ascorbic acid and potassium sorbate by different Lactobacillus species isolated from packed green olives

The aim of this research was to ascertain the lactic acid bacteria responsible for the degradation of ascorbic acid and/or potassium sorbate, isolated from packed green olives where these additives had diminished. A total of 14 isolates were recovered from samples of different green olive containers. According to partial sequencing of the 16S rRNA coding gene, Lactobacillus parafarraginis, Lactobacillus rapi, Lactobacillus pentosus, Lactobacillus paracollinoides, and Pediococcus ethanolidurans were identified. With the exception of L. pentosus and L. paracollinoides, the other species had not been mentioned in table olives before this study. Only three of the 14 isolates metabolized ascorbic acid in MRS broth, and the products from ascorbic acid in modified MRS broth without carbon sources were acetic and lactic acids. Except for the two L. rapi and the two P. ethanolidurans strains, the remaining 10 isolates depleted potassium sorbate added into MRS broth to some extent. The product generated by three of these strains was confirmed to be trans-4-hexenoic acid. The degradation of ascorbate or sorbate by lactic acid bacteria should be taken into account when these additives are used in food products where this group of bacteria may be present.     

Detection and partial characterization of a broad-range bacteriocin produced by Lactobacillus plantarum (ATCC 8014)

Lactobacillus plantarum (ATCC 8014) was tested for production of antimicrobial compounds. This study demonstrates that the cell-free supernatant of L. plantarum is effective in inhibiting the growth of a wide range of Gram-positive and Gram-negative bacteria including, Staphylococcus aureus, Escherichia coli, Listeria innocua, and Pseudomonas aeruginosa. The inhibitory compound lost activity when heated to temperatures greater than 30°C and when subjected to pH changes that lowered the pH below 4 or above 5. In addition, the inhibitory protein was susceptible to digestion by various proteases. The apparent molecular weight based on SDS-PAGE analysis is 122 KDa. These findings support the idea that the inhibitory compound is a protein and can be considered a bacteriocin secreted from the Gram-positive bacterium L. plantarum.     

Selection of Lactobacillus plantarum strains to use as starters in fermented table olives: Oleuropeinase activity and phage sensitivity

Fermented table olives (Olea europaea L.) are largely diffused in the Mediterranean area. Olives are picked at different stages of maturity and after harvesting, processed to eliminate the characteristic bitterness caused by the presence of the oleuropein glucoside and to become suitable for human consumption. The spontaneous fermentation of table olives mainly depends on lactic acid bacteria (LAB), and in particular on Lactobacillus plantarum which plays an important role in the degradation of oleuropein. The hydrolysis of oleuropein is attributed to the β-glucosidase and esterase activities of the indigenous LAB microflora. This study investigated the potential of L. plantarum strains isolated from dairy products and olives to be used as starters for fermented table olives. Forty-nine strains were typed by RAPD-PCR and investigated for the presence of the β-glucosidase (bglH) gene. The full sequence of the bglH gene was carried out. All the 49 L. plantarum strains were also tested for phage resistance. A total of six strains were selected on the basis of genotypic polymorphism, bglH gene sequence analysis, and phage resistance profile. These strains were further characterized to assess the acidifying capability, the growth at different temperatures, the tolerance to different NaCl concentrations, and the oleuropeinolytic activity. Although further characterizations are required, especially concerning the influence on sensory properties, L. plantarum proved to have the potential to be used as a debittering and fermentative agent in starter culture for fermented table olives.     

Formation of conjugated linoleic acid by a Lactobacillus plantarum strain isolated from an artisanal cheese: Evaluation in miniature cheeses

Among 129 lactic acid bacteria previously isolated from raw-milk starter-free cheeses manufactured in Galicia (NW Spain), two strains of Lactobacillus plantarum were definitely recognised as producers of conjugated linoleic acid (CLA). Gas chromatography analysis identified cis-9, trans-11 C18:2 as the predominant CLA isomer formed in MRS broth supplemented with linoleic acid. A centrifugation-based model for the manufacture of miniature cheeses was used to evaluate the formation of CLA by Lb. plantarum L200, the highest producer of CLA in MRS broth. The miniature cheeses made with the addition of the L200 strain showed significantly (P < 0.05) higher contents of cis-9, trans-11 CLA than those of the control cheeses (1.09 versus 0.69 percentage of total fatty acids, respectively). These results suggest that Lb. plantarum L200 strain could be used as an adjunct culture to slightly increase the concentrations of CLA in short-ripened cows' milk cheeses.     

Effect of inulin on growth and bacteriocin production by Lactobacillus plantarum in stationary and shaken cultures

The prebiotic effect of inulin added to MRS medium on growth and bacteriocin production by L. plantarum ST16 Pa was investigated in stationary cultures in anaerobic jars with medium containing 0.025% sodium thioglycolate or in flasks shaken at 100 rpm. In the presence of 1% inulin in anaerobic stationary cultures, this strain produced lactic acid at a level that was 36.5% higher than in the absence of the polysaccharide. In shaken cultures without inulin, cell count was 54% higher than in the stationary ones. Under stationary conditions in anaerobic jars, the addition of inulin increased the maximum specific growth rate from 0.37 to 0.49 h^?1 and reduced the generation time from 1.85 h to 1.40 h. Consequently, the exponential phase was shortened from 12 to 9 h when the cells were grown in stationary cultures with the oxygen scavenger. Despite this effect of inulin on growth rate, stationary cultures without inulin displayed higher antimicrobial activity against Listeria monocytogenes L104 (3200 AU/mL) than cultures with inulin (1600 AU/mL); therefore, inulin behaved as a compound able to accelerate growth rather than to stimulate bacteriocin production. The results presented in this study are very promising, as L. monocytogenes is a well‐known foodborne pathogenic microorganism. Moreover, L. plantarum ST16 Pa has proven to be a potential producer of a natural food preservative at an industrial level.     

Lactobacillus pentosus dominates spontaneous fermentation of Italian table olives

Culture-dependent and -independent approaches were applied to identify the bacterial species involved in Italian table olive fermentation. Bacterial identification showed that Lactobacillus pentosus was the dominant species although the presence of Lactobacillus plantarum, Lactobacillus casei, Enterococcus durans, Lactobacillus fermentum and Lactobacillus helveticus was observed. Rep-PCR allowed to obtain strain-specific profiles and to establish a correlation with table olive environment. PCR-DGGE (Denaturing Gradient Gel Electrophoresis) confirmed the heterogeneity of bacterial community structure in fermented table olives as well as the prevalence of L. pentosus. The strains were characterized on the basis of technological properties (NaCl tolerance, β-glucosidase activity and the ability to grow in synthetic brine and in presence of 1 g/100 mL oleuropein). L. pentosus showed a high capacity of adaptation to the different conditions characterizing the olive ecosystem. This species showed the highest percentage of strains able to grow in presence of 10 g/100 mL NaCl, oleuropein and in the synthetic brine. Moreover, all the strains belonging to L. pentosus and L. plantarum species showed a β-glucosidase activity. This study allowed both to identify the main species and strains associated to Italian table olives and to obtain a lactic acid bacteria collection to apply as starter culture in the process of olive fermentation.     

Short Communication: Culture-Independent Detection of Lactic Acid Bacteria Bacteriocin Genes in Two Traditional Slovenian Raw Milk Cheeses and Their Microbial Consortia

Two Slovenian traditional raw milk cheeses, Tolminc (from cows’ milk) and Kraški (from ewes’ milk), were examined for the presence of 19 lactic acid bacteria bacteriocin genes by PCR analysis of total DNA extracts from 9 cheeses and from consortia of strains isolated from these cheeses. Eleven bacteriocin genes were detected in at least one cheese or consortium, or from both. Different cheeses or consortia contained 3 to 9 bacteriocin determinants. Plantaricin A gene determinants were found in all cheese and consortia DNA extracts. Genes for enterocins A, B, P, L50A, and L50B, and the bacteriocin cytolysin were commonly detected, as were genes for nisin. These results indicate that bacteriocinogenic strains of Lactobacillus, Enterococcus, and Lactococcus genera with protective potential are common members of indigenous microbiota of raw milk cheeses, which can be a good source of new protective strains.