Linking Pélardon artisanal goat cheese microbial communities to aroma compounds during cheese-making and ripening

Pélardon is an artisanal French raw goat's milk cheese, produced using natural whey as a backslop. The aim of this study was to identify key microbial players involved in the acidification and aroma production of this Protected Designation of Origin cheese. Microbial diversity of samples, collected from the raw milk to 3-month cheese ripening, was determined by culture-dependent (MALDI-TOF analysis of 2877 isolates) and -independent (ITS2 and 16S metabarcoding) approaches and linked to changes in biochemical profiles (volatile compounds and acids). In parallel, potential dominant autochthonous microorganism reservoirs were also investigated by sampling the cheese-factory environment. Complex and increasing microbial diversity was observed by both approaches during ripening although major discrepancies were observed regarding Lactococcus lactis and Lacticaseibacillus paracasei fate. By correlating microbial shifts to biochemical changes, Lactococcus lactis was identified as the main acidifying bacterium, while L. mesenteroides and Geotrichum candidum were prevalent and associated with amino acids catabolism after the acidification step. The three species were dominant in the whey (backslop). In contrast, L. paracasei, Enterococcus faecalis, Penicillium commune and Scopulariopsis brevicaulis, which dominated during ripening, likely originated from the cheese-making environment. All these four species were positively correlated to major volatile compounds responsible for the goaty and earthy Pélardon cheese aroma. Overall, this work highlighted the power of MALDI-TOF and molecular techniques combined with volatilome analyses to dynamically follow and identify microbial communities during cheese-making and successively identify the key-players involved in aroma production and contributing to the typicity of Pélardon cheese.

Fermentation Enhanced Biotransformation of Compounds in the Kernel of Chrysophyllum albidum

Chrysophyllum albidum Linn (African star apple) is a fruit with extensive nutritional and medicinal benefits. The fruit and kernel in the seed are both edible. Strains of lactic acid bacteria (LAB) were isolated from fermented seeds and assessed for probiotic characteristics. The extracts in both the unfermented and the fermented aqueous extracts from the kernels obtained from the seeds of C. albidum were subjected to analysis using the gas chromatography/mass spectrometry (GC-MS) method. This analysis identified the bioactive compounds present as possible substrate(s) for the associated organisms inducing the fermentation and the resultant biotransformed products formed. Three potential probiotic LAB strains identified as Lactococcus raffinolactis (ProbtA1), Lactococcus lactis (ProbtA2a), and Pediococcus pentosaceus (ProbtA2b) were isolated from the fermented C. albidum seeds. All strains were non hemolytic, which indicated their safety, Probt (A1, A2a, and A2b) grew in an acidic environment (pH 3.5) during the 48-h incubation time, and all three strains grew in 1% bile, and exhibited good hydrophobicity and auto-aggregation properties. Mucin binding proteins was not detected in any strain, and bile salt hydrolase was detected in all the strains. l-lactic acid (28.57%), norharman (5.07%), formyl 7E-hexadecenoate (1.73%), and indole (1.51%) were the four major constituents of the fermented kernel of the C. albidum, while 2,5-dimethylpyrazine (C1, 1.27%), 3,5-dihydroxy-6-methyl-2,3-dihydropyran-4-one (C2, 2.90%), indole (C3, 1.31%), norharman (C4, 3.01%), and methyl petroselinate (C5, 4.33%) were the five major constituents of the unfermented kernels. The isolated LAB are safe for consumption. The fermenting process metabolized C1, C2, and C5, which are possible starter cultures for the growth of probiotics. Fermentation is an essential tool for bioengineering molecules in foods into safe and health beneficial products.

From Waste to Taste-Efficient Production of the Butter Aroma Compound Acetoin from Low-Value Dairy Side Streams Using a Natural (Nonengineered) Lactococcus lactis Dairy Isolate

Lactococcus lactis subsp. lactis biovar diacetylactis is widely used in dairy fermentations as it can form the butter aroma compounds acetoin and diacetyl from citrate in milk. Here, we explore the possibility of producing acetoin from the more abundant lactose. Starting from a dairy isolate of L. lactis biovar diacetylactis, we obtained a series of mutants with low lactate dehydrogenase (ldh) activity. One isolate, RD1M5, only had a single insertion mutation in the ldh gene compared to its parental strain as revealed by whole genome resequencing. We tested the ability of RD1M5 to produce acetoin in milk. With aeration, all the lactose could be consumed, and the only product was acetoin. In a simulated cheese fermentation, a 50% increase in acetoin concentration could be achieved. RD1M5 turned out to be an excellent cell factory for acetoin and was able to convert lactose in dairy waste into acetoin with high titer (41 g/L) and high yield (above 90% of the theoretical yield). Summing up, RD1M5 was found to be highly robust and to grow excellently in milk or dairy waste. Being natural in origin opens up for applications within dairies as well as for safe production of food-grade acetoin from low-cost substrates.

Design of microbial consortia for the fermentation of pea-protein-enriched emulsions

In order to encourage Western populations to increase their consumption of vegetables, we suggest turning legumes into novel, healthy foods by applying an old, previously widespread method of food preservation: fermentation. In the present study, a total of 55 strains from different microbial species (isolated from cheese or plants) were investigated for their ability to: (i) grow on a emulsion containing 100% pea proteins and no carbohydrates or on a 50:50 pea:milk protein emulsion containing lactose, (ii) increase aroma quality and reduce sensory off-flavors; and (iii) compete against endogenous micro organisms. The presence of carbohydrates in the mixed pea:milk emulsion markedly influenced the fermentation by strongly reducing the pH through lactic fermentation, whereas the absence of carbohydrates in the pea emulsion promoted alkaline or neutral fermentation. Lactic acid bacteria assigned to Lactobacillus plantarum, Lactobacillus rhamnosus, Lactococcus lactis and Lactobacillus casei species grew well in both the pea and pea:milk emulsions. Most of the fungal strains tested (particularly those belonging to the Mucor and Geotrichum genera) were also able to grow on both emulsions. Although most Actinobacteria and Proteobacteria did not compete with endogenous microbiota (Bacillus), some species such as Hafnia alvei, Acinetobacter johnsonii and Glutamicibacter arilaitensis grew strongly and appeared to restrict the development of the endogenous microbiota when the pea emulsion was inoculated with a combination of three to nine strains. In the mixed emulsions, lactic fermentation inhibited Actinobacteria and Proteobacteria (e.g. Brevibacterium casei, Corynebacterium casei, Staphylococcus lentus) to the greatest extent but also inhibited Bacillus (e.g. Bacillus subtilis and Bacillus licheniformis). Overall, this procedure enabled us to select two microbial consortia able to colonize pea-based products and positively influence the release of volatile compounds by generating a roasted/grilled aroma for the 100% pea emulsion, and a fruity, lactic aroma for the 50:50 pea:milk emulsion. Moreover, the fermentation in the pea-based emulsions reduced the level of hexanal, which otherwise leads to an undesired green pea aroma. Our present results show how the assembly of multiple microbial cultures can help to develop an innovative food product.

High-throughput screening for texturing Lactococcus strains

In the food industry, lactic acid bacteria (LAB) are used in dairy fermentations, extending the shelf life by lowering the pH and also affecting taste and texture of the fermented milk. The texture of fermented milk is an important quality parameter, affecting consumer acceptance. Finding LAB providing desired texture of a product is time consuming and laborious when using standard methods for measuring texture, e.g. rheology measurements. Screening of 986 Lactococcus lactis strains resulted in few strains with the ability to enhance texture, demonstrating the necessity of implementation of high-throughput screening methods. A high-throughput screening assay was developed, combining small-scale 96-well microtiter plates and pressure measurements during liquid handling, e.g. aspiration, to find strains that give good texture in fermented milk. Only about 1% of the strains were found to enhance milk texture. Two of the texturing strains belong to L. lactis subsp. lactis, which are the first texturing strains from this subsp. reported. Mining for eps gene clusters responsible for exocellular polysaccharide production was performed, as polysaccharide production can contribute positively to fermented milk texture. Comparative genomics approach revealed four types of texturing L. lactis strains with diverse eps gene clusters.

Infective endocarditis caused by Lactococcus lactis subsp. lactis and Pediococcus pentosaceus: A case report and literature review

RATIONALE

Lactococcus lactis and Pediococcus pentosaceus are rare pathogens which rarely caused infections in humans. Several cases with L. lactis endocarditis have been reported in the literature, among them few were caused by L. lactis subsp. Lactis. Opportunistic P. pentosaceus infections were rarely reported.

PATIENT CONCERNS

A 66-year-old man presented to our hospital due to persistent fever for 15 days. A physical checking revealed a grade II holosystolic murmur at the heart apex. A chest computed tomography (CT) scan suggested bronchitis. L. lactis subsp. lactis was identified in blood cultures. Transthoracic and transesophageal echocardiography revealed the presence of a large hyperechogenic mass in the left atrium, and a large floating vegetation on the mitral valve with a severe mitral regurgitation.

DIAGNOSIS

Infectious endocarditis caused by L. lactis subsp. Lactis was diagnosed.

INTERVENTIONS

Levofloxacin (0.5 g/day) was used for 20 days; however, L. lactis subsp. lactis remained to be isolated from blood culture. Therefore, vancomycin (2 g/day) was used to replace levofloxacin. Six days after the treatment with vancomycin, the blood culture revealed no L. lactis subspecies lactis, but yielded a growth of gram-positive and non-spore forming cocci; and P. pentosaceus was identified. Antimicrobial susceptibility test revealed P. pentosaceus was sensitive to penicillin and levofloxacin. Vancomycin was discontinued, and levofloxacin (0.5 g/day) was restarted and treated for another 7 days. The patient recovered with negative blood culture results, and discharged from the hospital.

OUTCOMES

The patient recovered with negative blood culture results, and discharged from the hospital.

LESSONS

Our patient had a long-period of antibiotic treatment with strategy alterations. Standard interpretation criteria of Clinical and Laboratory Standards Institute (CLSI) for L. lactis should be established, and molecular tests will increase the identification rate of L. lactis infections.

Cheese brines from Danish dairies reveal a complex microbiota comprising several halotolerant bacteria and yeasts

The Danish Danbo cheese is a surface ripened semi-hard cheese, which before ripening is submerged in brine for up to 24 h. The brining is required in order to obtain the structural and organoleptic properties of the cheeses. Likewise, the content of NaCl in the cheese will influence especially the surface microbiota being of significant importance for flavour development and prevention of microbial spoilage. Even though the microbiota on cheese surfaces have been studied extensively, limited knowledge is available on the occurrence of microorganisms in cheese brine. The aim of the present study was to investigate by both culture-dependent and -independent techniques the brine microbiota in four Danish dairies producing Danbo cheese. The pH of the brines varied from 5.1 to 5.6 with a dry matter content from 20 to 27% (w/w). The content of lactate varied from 4.1 to 10.8 g/L and free amino acids from 65 to 224 mg/L. Bacteria were isolated on five different media with NaCl contents of 0.85-23.0% (w/v) NaCl. The highest count of 6.3 log CFU/mL was obtained on TSA added 4% (w/v) NaCl. For yeasts, the highest count was 3.7 log CFU/mL on MYGP added 8% (w/v) NaCl. A total of 31 bacterial and eight eukaryotic species were isolated including several halotolerant and/or halophilic species. Among bacteria, counts of ≥6.0 log CFU/mL were obtained for Tetragenococcus muriaticus and Psychrobacter celer, while counts between ≥4.5 and < 6.0 log CFU/mL were obtained for Lactococcus lactis, Staphylococcus equorum, Staphylococcus hominis, Chromohalobacter beijerinckii, Chromohalobacter japonicus and Microbacterium maritypicum. Among yeasts, counts of ≥3.5 log CFU/mL were only obtained for Debaryomyces hansenii. By amplicon-based high-throughput sequencing of 16S rRNA gene and ITS2 regions for bacteria and eukaryotes respectively, brines from the same dairy clustered together indicating the uniqueness of the dairy brine microbiota. To a great extent the results obtained by amplicon sequencing fitted with the culture-dependent technique though each of the two methodologies identified unique genera/species. Dairy brine handling procedures as e.g. microfiltration were found to influence the brine microbiota. The current study proves the occurrence of a specific dairy brine microbiota including several halotolerant and/or halophilic species most likely of sea salt origin. The importance of these species during especially the initial stages of cheese ripening and their influence on cheese quality and safety need to be investigated. Likewise, optimised brine handling procedures and microbial cultures are required to ensure an optimal brine microbiota.

The effect of immunoregulation of Streptococcus lactis L16 strain upon Staphylococcus aureus infection

BACKGROUND

Staphylococcus aureus is an important pathogen that causes various infections in medical facilities. However, resistance to multiple drugs has made this infection difficult to manage. Thus, new therapeutic strategies are urgently needed to solve this worldwide public health problem. The Streptococcus lactis L16 strain was isolated from the fermented hot chili sauce. To explore whether it can be used as a protective agent against S. aureus infection, we designed a mouse model of S. aureus infection to evaluate the therapeutic potency of S. lactis. Mice were grouped into pre-(P) and post-(T) S. aureus infection groups following oral administration of S. lactis L16. The protection and treatment effects were assessed by examining body weight, internal organ weight, serum cytokines and intestinal secretory IgA alternations.

RESULT

Oral administration of the S. lactis L16 strain reduced the loss of body weight in mice post-infection and alleviated infection-induced hepatomegaly. In particular, the PL16 group (protection with L16) showed more effective resistance to S. aureus than the TL16 group (treatment with L16). The level of serum cytokine interferon gamma following oral administration of the L16 strain was remarkably increased during infection, as were interleukin-4 levels during convalescence. The probiotic L16 strain induced more sIgA production than S. aureus.

CONCLUSION

Our data suggest that S. lactis L16 is an effective strain with anti-Staphylococcus activity. By regulating the Th1/Th2 response, S. lactis can effectively reduce lesions from infection, indicating its therapeutic potential in overcoming antibiotic resistance in this mouse infection model that mimics infections observed in humans.

Cadmium tolerant characteristic of a newly isolated Lactococcus lactis subsp. lactis

Environmental contamination caused by heavy metals poses a major threat to the wildlife and human health for their toxicity and intrinsically persistent nature. Some specific food grade bacteria have properties that enable them to eliminate heavy metals from food and water. Lactococcus lactis subsp. lactis, newly isolated from pickles, is a cadmium (Cd) tolerant bacteria. Cd resistant properties of the lactis was evaluated under different Cd stresses. Cd accumulation in different cellular parts was determined by ICP-MS and cell morphology changes were measured by SEM-EDS and TEM-EDS. In addition, functional groups associated with Cd resistance were detected by infrared spectroscopic analysis. The results indicated that Cd mainly accumulated in the cell surface structures including cytoderm and cytomembrane. Functional groups such as OH and NH₂ in the cell surface played essential roles in Cd biosorption. The elements of O, P, S, and N of polysaccharide, membrane protein and phosphatidate in the cell surface structures might be responsible for Cd biosorption for their strong electronegativity. This study indicated that ultrastructural analysis can be a supplemental method to study heavy metal resistance mechanism of microorganism and the newly isolated lactococcus lactis subsp. lactis has great potential to be applied to decontamination of heavy metals.

Characterization of a cadmium resistance Lactococcus lactis subsp. lactis strain by antioxidant assays and proteome profiles methods

Heavy metal contamination poses a major threat to the environment and human health for their potential toxicity and non-biodegradable properties. At present, some probiotics bacteria are reported to have great potential to eliminate heavy metals from food and water. In this study, resistance properties of a newly isolated Lactococcus lactis subsp. lactis for cadmium were studied by antioxidant assays and proteomics analysis. Antioxidant capacity of this strain was significantly activated under cadmium stress indicated by Fenton reaction, DPPH assay, SOD assay and GSH assay. Intracellular antioxidant enzyme systems, such as superoxide dismutase, glutathione reductase and catalase were suggested to play vital roles in the activated antioxidant capacity. The up-regulated cadA was associated with the activated P-type ATPases that plays an important role in cadmium resistance. Proteomics analysis identified 12 over-expressed proteins under 50mg/L cadmium stress and these proteins are abundant in oxidative stress response and energy metabolism regulation, which were considered as consequences as cadmium resistance of the strain. Thus, the probiotics Lactococcus lactis subsp. lactis may resist cadmium stress through antioxidant approach and enhanced energy metabolism. The food grade lactis strain may be applied in metal decontamination in environment and food/feed.

Mesophilic Lactic Acid Bacteria Diversity Encountered in Brazilian Farms Producing Milk with Particular Interest in Lactococcus lactis Strains

The milk produced in regions with different traditions in Brazil is used for artisanal product production, which is characterized by different sensorial characteristics. This study aimed to identify the bacterial ecosystem of farms located in a traditional dairy region in the state of Minas Gerais and to characterize Lactococcus lactis strains, the species of interest in this study, using a multilocus sequence typing (MLST) protocol and pulsed-field gel electrophoresis (PFGE) technique. Samples were collected from raw milk and dairy environment from six farms. A total of 50 isolates were analyzed using 16S rRNA sequencing and species-specific PCR. Five genera were identified: Lactobacillus, Leuconostoc, Lactococcus, Enterococcus, and Staphylococcus, from ten different species. MLST (with six housekeeping genes) and PFGE (with SmaI endonuclease) were used for the characterization of 20 isolates of Lactococcus lactis from a dairy collection in this study. Both methods revealed a high clonal diversity of strains with a higher discriminatory level for PFGE (15 pulsotypes), compared to MLST (12 ST). This study contributes to the preservation of the Brazilian dairy heritage and provides insights into a part of the LAB population found in raw milk and dairy environment.

Genetic Characterization of Lactic Acid Bacteria Isolated from Tunisian Milk Waste and their Antimicrobial Activity Against some Bacteria Implicated in Nosocomial Infections

BACKGROUND

A total of 94 lactic acid bacteria (LAB) were isolated from Tunisian artisanal (Ricotta cheese's whey) and industrial (bactofugate) milk waste, identified and then screened for their antimicrobial activity against some bacteria implicated on nosocomial infections.

OBJECTIVE

Bacterial genera and species identification was performed using molecular tools. The antimicrobial activity was tested against 7 strains of Gram-negative bacteria and 4 strains of Gram-positive bacteria as well as 6 yeasts.

METHOD

The Crude extract was found to have a narrow antimicrobial spectrum on Gram-positive bacteria mainly Listeria monocytogenes. Among the strains which showed antibacterial activity, four were determined to be bacteriocins-producers. They were identified as Lactococcus lactis.

RESULTS

Brain Heart Infusion (BHI) Agar was found more adapted than Man, Rogosa and Sharpe (MRS) to investigate the antimicrobial activity of L. actococcus lactis against L. isteria monocytogenes. The genetic determinants encoding the antimicrobial peptides were targeted by specific PCR.

CONCLUSION

All L. lactis bacteriocin producing strains possessed the Nisine Z gene (nisZ) except for one, which contained both Nisine A and Nisine Z genes (nisA and nisZ). They have been identified as antilisterial agentS.

PFGE protocols to distinguish subspecies of Lactococcus lactis

Pulsed-field gel electrophoresis (PFGE), developed in the mid-1980s, rapidly became a "gold standard" method for analyzing bacterial chromosomes. Today, although outcompeted in resolution by alternative methods, such as optical mapping, and not applicable for high-throughput analyses, PFGE remains a valuable method for bacterial strain typing. Here, we describe optimized protocols for macrorestriction fingerprinting, characterization of plasmid complements, and gene localization by DNA-DNA hybridization of Lactococcus lactis genomes.

Evaluation of Lactococcus lactis Isolates from Nondairy Sources with Potential Dairy Applications Reveals Extensive Phenotype-Genotype Disparity and Implications for a Revised Species

Lactococcus lactis is predominantly associated with dairy fermentations, but evidence suggests that the domesticated organism originated from a plant niche. L. lactis possesses an unusual taxonomic structure whereby strain phenotypes and genotypes often do not correlate, which in turn has led to confusion in L. lactis classification. A bank of L. lactis strains was isolated from various nondairy niches (grass, vegetables, and bovine rumen) and was further characterized on the basis of key technological traits, including growth in milk and key enzyme activities. Phenotypic analysis revealed all strains from nondairy sources to possess an L. lactis subsp. lactis phenotype (lactis phenotype); however, seven of these strains possessed an L. lactis subsp. cremoris genotype (cremoris genotype), determined by two separate PCR assays. Multilocus sequence typing (MLST) showed that strains with lactis and cremoris genotypes clustered together regardless of habitat, but it highlighted the increased diversity that exists among "wild" strains. Calculation of average nucleotide identity (ANI) and tetranucleotide frequency correlation coefficients (TETRA), using the JSpecies software tool, revealed that L. lactis subsp. cremoris and L. lactis subsp. lactis differ in ANI values by ∼14%, below the threshold set for species circumscription. Further analysis of strain TIFN3 and strains from nonindustrial backgrounds revealed TETRA values of <0.99 in addition to ANI values of <95%, implicating that these two groups are separate species. These findings suggest the requirement for a revision of L. lactis taxonomy.

Bacteriocinogenic Lactococcus lactis subsp. lactis DF04Mi isolated from goat milk: Application in the control of Listeria monocytogenes in fresh Minas-type goat cheese

Listeria monocytogenes is a pathogen frequently found in dairy products. Its control in fresh cheeses is difficult, due to the psychrotrophic properties and salt tolerance. Bacteriocinogenic lactic acid bacteria (LAB) with proven in vitro antilisterial activity can be an innovative technological approach but their application needs to be evaluated by means of in situ tests. In this study, a novel bacteriocinogenic Lactococcus lactis strain ( Lc . lactis DF4Mi), isolated from raw goat milk, was tested for control of growth of L. monocytogenes in artificially contaminated fresh Minas type goat cheese during storage under refrigeration. A bacteriostatic effect was achieved, and counts after 10 days were 3 log lower than in control cheeses with no added LAB. However, this effect did not differ significantly from that obtained with a non-bacteriocinogenic Lc. lactis strain. Addition of nisin (12.5 mg/kg) caused a rapid decrease in the number of viable L. monocytogenes in the cheeses, suggesting that further studies with the purified bacteriocin DF4Mi may open new possibilities for this strain as biopreservative in dairy products.

Acquisition through horizontal gene transfer of plasmid pSMA198 by Streptococcus macedonicus ACA-DC 198 points towards the dairy origin of the species

Background

Streptococcus macedonicus is an intriguing streptococcal species whose most frequent source of isolation is fermented foods similarly to Streptococcus thermophilus. However, S. macedonicus is closely related to commensal opportunistic pathogens of the Streptococcus bovis/Streptococcus equinus complex.

Methodology/Principal Findings

We analyzed the pSMA198 plasmid isolated from the dairy strain Streptococcus macedonicus ACA-DC 198 in order to provide novel clues about the main ecological niche of this bacterium. pSMA198 belongs to the narrow host range pCI305/pWV02 family found primarily in lactococci and to the best of our knowledge it is the first such plasmid to be reported in streptococci. Comparative analysis of the pSMA198 sequence revealed a high degree of similarity with plasmids isolated from Lactococcus lactis strains deriving from milk or its products. Phylogenetic analysis of the pSMA198 Rep showed that the vast majority of closely related proteins derive from lactococcal dairy isolates. Additionally, cloning of the pSMA198 ori in L. lactis revealed a 100% stability of replication over 100 generations. Both pSMA198 and the chromosome of S. macedonicus exhibit a high percentage of potential pseudogenes, indicating that they have co-evolved under the same gene decay processes. We identified chromosomal regions in S. macedonicus that may have originated from pSMA198, also supporting a long co-existence of the two replicons. pSMA198 was also found in divergent biotypes of S. macedonicus and in strains isolated from dispersed geographic locations (e.g. Greece and Switzerland) showing that pSMA198’s acquisition is not a recent event.

Conclusions/Significance

Here we propose that S. macedonicus acquired plasmid pSMA198 from L. lactis via an ancestral genetic exchange event that took place most probably in milk or dairy products. We provide important evidence that point towards the dairy origin of this species.

From field to fermentation: the origins of Lactococcus lactis and its domestication to the dairy environment

Lactococcus lactis is an organism of substantial economic importance, used extensively in the production of fermented foods and widely held to have evolved from plant strains. The domestication of this organism to the milk environment is associated with genome reduction and gene decay, and the acquisition of specific genes involved in protein and lactose utilisation by horizontal gene transfer. In recent years, numerous studies have focused on uncovering the physiology and molecular biology of lactococcal strains from the wider environment for exploitation in the dairy industry. This in turn has facilitated comparative genome analysis of lactococci from different environments and provided insight into the natural phenotypic and genetic diversity of L. lactis. This diversity may be exploited in dairy fermentations to develop products with improved quality and sensory attributes. In this review, we discuss the classification of L. lactis and the problems that arise with phenotype/genotype designation. We also discuss the adaptation of non-dairy lactococci to milk, the traits associated with this adaptation and the potential application of non-dairy lactococci to dairy fermentations.

Isolation of lactic acid bacteria from kuruma shrimp (Marsupenaeus japonicus) intestine and assessment of immunomodulatory role of a selected strain as probiotic

Fifty-one lactic acid bacteria (LAB) strains were isolated and identified based on 16S ribosomal DNA sequence from the intestinal tracts of 142 kuruma shrimps (Marsupenaeus japonicus) collected from Kanmon Strait, Fukuoka and Tachibana Bay, Nagasaki, Japan. Cellular immunomodulatory function of 51 isolated LAB strains was assessed by measuring the level of interferon (IFN)-γ induction in mouse spleen cell culture. The strain Lactococcus lactis D1813 exhibited the highest amount of IFN-γ production and also bactericidal activity and was selected for testing its immunomodulatory role as a probiotic in kuruma shrimp. We also assessed the effect of dietary incorporation of this probiotic on resistance to Vibrio penaeicida infection in the kuruma shrimp. Our results demonstrate that probiotic L. lactis D1813-containing diet-fed (10⁵ cfu g⁻¹) shrimps displayed a significant up-regulation of lysozyme gene expressions in the intestine and hepatopancreas. However, insignificantly higher expression of anti-lipopolysaccharide factor, super oxide dismutase, prophenoloxidase, and toll-like receptor 1 was recorded in the intestine of shrimps fed the probiotic diet. Moreover, significantly increased (P < 0.01) resistance to the bacterial pathogen in term of better post-infection survival (61.7 %) was observed in the shrimps fed with the probiotic-incorporated diet compared with the control diet-fed group (28.3 %). The present study indicates the immunomodulatory role of the LAB L. lactis D1813 on the kuruma shrimp immune system and supports its potential use as an effective probiotic in shrimp aquaculture.

Lactococcosis in Silver Carp

An adult Silver Carp Hypophthalmichthys molitrix with a focally extensive skin lesion near the caudal peduncle and mild iridial hemorrhage was submitted to the Aquatic Research and Diagnostic Laboratory (ARDL) in Stoneville, Mississippi, as part of a fish kill investigation. Touch impressions of this musculoskeletal lesion revealed small cocci (∼1 μm) in pairs or chains within an inflammatory milieu. A pure Gram-positive cocci isolate was obtained from the brain, while cultures of the kidney and muscle yielded multiple bacterial colony types, including the Gram-positive cocci seen in the brain. This brain isolate was characterized biochemically and identified as Lactococcus spp. Analysis of the near complete 16S small subunit ribosomal DNA (SSU rDNA) and DNA gyrase subunit B (gyrB) gene sequences revealed the bacterium to be L. lactis subsp. lactis (SSU rDNA: 100% identity, 1,372/1,372 bp; gyrB: 99.7% identity, 1,779/1,785 bp). Comparatively, at the gyrB locus the case isolate shared less than 90% similarity to L. lactis subsp. cremoris (1,599/1,781 bp) and less than 80% homology to L. garvieae (1409/1775 bp). Histopathological examination confirmed a severe meningoencephalitis, a moderate mononuclear myositis, and a mild interstitial nephritis. We believe this represents the first report of a natural infection by L. lactis subsp. lactis in Silver Carp.

Identification of genomic heterogeneity among Lactococcus lactis strains by plasmid profiling, PFGE and 16S rDNA sequence analysis

Lactococcus lactis strains are used commonly as starters, which contribute to desirable flavour and texture properties known as strain-specific, in dairy industry. Genomic heterogeneity of 30 L. lactis strains originating from Turkey and characterized phenotypically were investigated in this study. Plasmid profiling, PFGE and 16S rDNA sequence analyses were performed to determine the genetic variability of strains. High degree of heterogeneity was detected among the L. lactis strains. Plasmid profiles of strains showed that compared to the plasmid free control strains, namely; L. lactis subsp. lactis IL1403 and L. lactis subsp. cremoris MG1614, all tested strains carried one to ten plasmids with molecular size ranging from 1.5 to 41.5kb. The fingerprints of strains obtained by PFGE from digestion with ApaI, SmaI and I-CeuI restriction endonucleases of chromosomal DNA's were compared with each other. All strains out of four were grouped into a large cluster A with at least 44% similarity level. The other four strains formed a minor duster B, distinctively different from major cluster A. PFGE results were confirmed by 16S rDNA sequence analysis and strains included in cluster B were identified as members of different species. These results suggested that morphologic and biochemical methods should be verified by reliable molecular approaches for the purpose of strain typing. Also, PFGE was found suitable to determine genomic differentiations among inter- and intra species.

Characteristics of microbial biofilm on wooden vats ('gerles') in PDO Salers cheese

The purpose of this study was to characterize microbial biofilms from 'gerles' (wooden vats for making PDO Salers cheese) and identify their role in milk inoculation and in preventing pathogen development. Gerles from ten farms producing PDO Salers cheese were subjected to microbial analysis during at least 4 periods spread over two years. They were distinguished by their levels of Lactobacillus (between 4.50 and 6.01 log CFU/cm(2)), Gram negative bacteria (between 1.45 and 4.56 log CFU/cm(2)), yeasts (between 2.91 and 5.57 log CFU/cm(2)), and moulds (between 1.72 and 4.52 log CFU/cm(2)). They were then classed into 4 groups according their microbial characteristics. These 4 groups were characterized by different milk inoculations (with either sour whey or starter culture, daily or not), and different washing procedures (with water or whey from cheese making). The farm gerles were not contaminated by Salmonella, Listeria monocytogenes or Staphylococcus aureus. Only one slight, punctual contamination was found on one gerle among the ten studied. Even when the milk was deliberately contaminated with L. monocytogenes and S. aureus in the 40 L experimental gerles, these pathogens were found neither on the gerle surfaces nor in the cheeses. Using 40 L experimental gerles it was shown that the microbial biofilms on the gerle surfaces formed in less than one week and then remained stable. They were mainly composed of a great diversity of lactic acid bacteria (Leuconostoc pseudomesenteroides, Lactococcus lactis, Lactobacillus casei, Lactobacillus plantarum, Lactobacillus hilgardii,…), Gram positive catalase positive bacteria (Curtobacterium flaccumfaciens, Curtobacterium oceanosedimentum Citrococcus spp., Brachybacterium rhamnosum, Kocuria rhizophila, Arthrobacter spp.…) and yeast (Kluyveromyces lactis, Kluyveromyces marxianus). In less than 1 min, even in a 500 L farm gerle, the gerle's microbial biofilm can inoculate pasteurized milk with micro-organisms at levels superior to those in raw milk.

Purification and partial characterization of bacteriocin produced by Lactococcus lactis ssp. lactis LL171

Lactic acid bacteria (LAB) are possessing ability to synthesize antimicrobial compounds (like bacteriocin) during their growth. In this regard, novel bacteriocin compound secreting capability of LAB isolated from Tulum Cheese in Turkey was demonstrated. The synthesized bacteriocin was purified by ammonium sulphate precipitation, dialysis and gel filtration. The molecular weight (≈3.4 kDa) of obtained bacteriocin was confirmed by SDS-PAGE, which revealed single peptide band. Molecular identification of LAB strain isolated from Tulum Cheese was conducted using 16S rDNA gene sequencing as Lactococcus lactis ssp. lactis LL171. The amino acid sequences (KKIDTRTGKTMEKTEKKIELSLKNMKTAT) of the bacteriocin from Lactococcus lactis ssp. lactis LL171 was found unique and novel than reported bacteriocins. Further, the bacteriocin was possessed the thermostable property and active at wide range of pH values from 1 to 11. Thus, bacteriocin reported in this study has the potential applications property as food preservative agent.

Plasmids of raw milk cheese isolate Lactococcus lactis subsp. lactis biovar diacetylactis DPC3901 suggest a plant-based origin for the strain

The four-plasmid complement of the raw milk cheese isolate Lactococcus lactis subsp. lactis biovar diacetylactis DPC3901 was sequenced, and some genetic features were functionally analyzed. The complete sequences of pVF18 (18,977 bp), pVF21 (21,739 bp), pVF22 (22,166 bp), and pVF50 (53,876 bp) were obtained. Each plasmid contained genes not previously described for Lactococcus, in addition to genes associated with plant-derived lactococcal strains. Most of the novel genes were found on pVF18 and encoded functions typical of bacteria associated with plants, such as activities of plant cell wall modification (orf11 and orf25). In addition, a predicted high-affinity regulated system for the uptake of cobalt was identified (orf19 to orf21 [orf19-21]), which has a single database homolog on a plant-derived Leuconostoc plasmid and whose functionality was demonstrated following curing of pVF18. pVF21 and pVF22 encode additional metal transporters, which, along with orf19-21 of pVF18, could enhance host ability to uptake growth-limiting amounts of biologically essential ions within the soil. In addition, vast regions from pVF50 and pVF21 share significant homology with the plant-derived lactococcal plasmid pGdh442, which is indicative of extensive horizontal gene transfer and recombination between these plasmids and suggests a common plant niche for their hosts. Phenotypes associated with these regions include glutamate dehydrogenase activity and Na(+) and K(+) transport. The presence of numerous plant-associated markers in L. lactis DPC3901 suggests a plant origin for the raw milk cheese isolate and provides for the first time the genetic basis to support the concept of the plant-milk transition for Lactococcus strains.

Detection and isolation of p-nitrophenol-lowering bacteria from intestine of marine fishes caught in Japanese waters

To determine the existence of p-nitrophenol (PNP)-lowering bacteria in intestine of Japanese coastal fish, the gastro-intestinal contents were incubated in Brain Heart Infusion (BHI) broth and minimal medium (MM) broths containing 1 mmol/L PNP at 30 °C for 7 days. Among 26 samples of 19 fish species, 17 samples showed a decrease in PNP of 0.5-0.8 mmol/L in BHI broth, but no decrease was shown in MM broth. Eighteen PNP-lowering bacterial strains were isolated from four fishes. All of the strains were identified as Lactococcus lactis subsp. lactis. Three L. lactis strains JS1-3 isolated from Japanese seabass Lateolabrax japonicus showed the highest PNP-lowering activity (0.44 mmol/L). Optimum temperature and pH for the growth and PNP decreasing corresponded with the marine environment. These results suggested that marine fishes have PNP decreasing bacteria in their intestine. These bacteria might protect host fish from toxicities of PNP and PNP related compounds.

Liver abscess and empyema due to Lactococcus lactis cremoris

Lactococcus lactis cremoris infections are very rare in humans. We experienced liver abscess and empyema due to L. lactis cremoris in an immunocompetent adult. A 42-yr-old man was admitted with fever and abdominal pain. Abdominal computed tomography (CT) revealed a liver abscess and chest CT showed loculated pleural effusion consistent with empyema. L. lactis cremoris was isolated from culture of the abscess material and blood. The patient was treated with pus drainage from liver abscess, video-assisted thoracoscopic decortications for empyema, and antibiotics including cefotaxime and levofloxacin. The patient was completely recovered with the treatment. To our knowledge, this is the first report of a L. lactis cremoris infection in Korea.

Joseph Lister: first use of a bacterium as a 'model organism' to illustrate the cause of infectious disease of humans

Joseph Lister's goal was to show that a pure culture of Bacterium lactis, normally present in milk, uniquely caused the lactic acid fermentation of milk. To demonstrate this fact he devised a procedure to obtain a pure clonal population of B. lactis, a result that had not previously been achieved for any microorganism. Lister equated the process of fermentation with infectious disease and used this bacterium as a model organism, demonstrating its role in fermentation; from this result he made the inductive inference that infectious diseases of humans are the result of the growth of specific, microscopic, living organisms in the human host.

Peritonitis due to Lactococcus lactis in a CAPD patient

Lactococcus lactis is a gram-positive bacterium, commonly used in the dairy industry. Although Lactococcus lactis is known to be non-pathogenic for humans, it can cause infection in immunocompromised patients. We report a case of peritonitis due to L. lactis in a continuous ambulatory peritoneal dialysis patient, which is the second reported case in the literature.

Detection and identification of bacteria in an isolated system with near-infrared spectroscopy and multivariate analysis

Near-infrared (NIR) transflectance spectra of Listeria innocua FH, Lactococcus lactis, Pseudomonas fluorescens, Pseudomonas mendocina, and Pseudomonas putida suspensions were collected and investigated for their potential use in the identification and classification of bacteria. Unmodified spectral data were transformed (first and second derivative) using the Savitzsky-Golay algorithm. Principal component analysis (PCA), partial least-squares discriminant analysis (PLS2-DA), and soft independent modeling of class analogy (SIMCA) were used in the analysis. Using either full cross-validation or separate calibration and prediction data sets, PLS2 regression classified the five bacterial suspensions with 100% accuracy at species level. At Pseudomonas genus level, PLS2 regression classified the three Pseudomonas species with 100% accuracy. In the case of SIMCA, prediction of an unknown sample set produced correct classification rates of 100% except for L. innocua FH (77%). At genus level, SIMCA produced correct classification rates of 96.7, 100, and 100% for P. fluorescens, P. mendocina, and P. putida, respectively. This successful investigation suggests that NIR spectroscopy can become a useful, rapid, and noninvasive tool for bacterial identification.

Lactococcus lactis subspecies lactis also causes white muscle disease in farmed giant freshwater prawns Macrobrachium rosenbergii

From May to August 2001 in Taiwan, 27 farms for the giant freshwater prawn Macrobrachium rosenbergii experienced white tail disease outbreaks in animals approximately 3 to 5 mo old, with total lengths from 6 to 8 cm. Examination of the infected prawns revealed not only previously reported Lactococcus garvieae (16 farms) but also the novel L. lactis subsp. lactis (10 farms). One farm had shrimp infected with both bacteria. In the farms with L. lactis infections, the cumulative mortality was approximately 25 to 60%. Gross signs of disease were opaque and whitish muscles, while histopathology included marked edema and necrotic lesions, with inflammation in the muscles and hepatopancreas. Bacteria isolated using brain/heart infusion medium or tryptic soy agar were Gram-positive and ovoid. Eleven isolates from different farms were identified as L. lactis subsp. lactis using API 20 Strep and Rapid ID32 Strep tests and using PCR assays specific for the L. lactis subsp. lactis 16S rDNA gene (650 bp amplicon) and for the 16S to 23S rDNA interspacer region (380 bp amplicon). In addition, sequencing of the full 16S rDNA genes of 2 of the isolates (MR17 and MR26; GenBank Accession Numbers AF493058 and AF493057, respectively) revealed 99.9% identity between the isolates and 98.7% identity to several complete 16S rRNA sequences of L. lactis subsp. lactis at GenBank. Experimental infections with our isolates gave gross signs and histopathological changes similar to those seen in naturally infected prawns. The mean lethal dose of 4 isolates and the reference strain L. lactis subsp. lactis BCRC 10791 ranged from 4.2 x 10(6) to 2.5 x 10(7) colony-forming units prawn(-1), indicating virulence similar to that previously reported for L. garvieae. This is the first report confirming L. lactis subsp. lactis as a pathogen in juvenile and adult prawns from aquaculture.

Partial characterization of bacteriocins produced by human Lactococcus lactis and Pediococccus acidilactici isolates

AIMS

The aim of this study was to isolate bacteriocin-producing lactic acid bacteria (LAB) from human intestine.

METHODS AND RESULTS

A total of 111 LAB were isolated from human adult stool and screened for their bacteriocin production. Neutralized cell-free supernatants from Lactococcus lactis subsp. lactis MM19 and Pediococcus acidilactici MM33 showed antimicrobial activity. The antimicrobials in the supernatant from a culture of L. lactis inhibited Enterococcus faecium, various species of Lactobacillus and Staphylococcus aureus; while those in the supernatant from a culture of P. acidilactici inhibited Enterococcus spp., some lactobacilli and various serotypes of Listeria monocytogenes. The antimicrobial metabolites were heat-stable and were active over a pH range of 2-10. The antimicrobial activities of the supernatants of both bacteria were inhibited by many proteases but not by catalase. The plate overlay assay allowed an approximation of size between 3.5 and 6 kDa for both antimicrobial substances.

CONCLUSIONS

As the antagonistic factor(s) produced by L. lactis MM19 and P. acidilactici MM33 were sensitive to proteolytic enzymes, it could be hypothesized that bacteriocins were involved in the inhibitory activities. Inhibition spectrum and biochemical analysis showed that these bacteria produced two distinct bacteriocins.

SIGNIFICANCE AND IMPACT OF THE STUDY

We are the first to isolate bacteriocin-producing strains of Pediococcus and Lactococcus from human intestine. These strains might be useful for control of enteric pathogens.

Phenotypic and molecular characterization of Lactococcus lactis from milk and plants

AIMS

The aim of this study was to obtain new Lactococcus lactis strains from nondairy materials for use as milk fermentation starters. The genetic and phenotypic traits of the obtained strains were characterized and compared with those of L. lactis strains derived from milk. It was confirmed that the plant-derived bacteria could be used as milk fermentation starters.

METHODS AND RESULTS

About 2600 lactic acid bacteria were subjected to screening for L. lactis with species-specific PCR. Specific DNA amplification was observed in 106 isolates. Forty-one strains were selected, including 30 strains of milk-derived and 11 of plant-derived, and their phenotypic traits and genetic profiles were determined. The plant-derived strains showed tolerance for high salt concentration and high pH value, and fermented many more kinds of carbohydrates than the milk-derived strains. There were no remarkable differences in the profiles of enzymes, such as lipases, peptidases and phosphatases. Isolates were investigated by cluster analysis based on randomly amplified polymorphic DNA profiles. There were no significant differences between isolates from milk and those from plant. The L. lactis subsp. cremoris strains were clustered into two distinct groups, one composed of the strains having the typical cremoris phenotype and the other composed of strains having a phenotype similar to subsp. lactis. Fermented milk manufactured using the plant-derived strains were not inferior in flavour to that manufactured using the milk-derived strains.

CONCLUSIONS

Plant-derived L. lactis strains are genetically close to milk-derived strains but have various additional capabilities, such as the ability to ferment many additional kinds of carbohydrates and greater stress-tolerance compared with the milk-derived strains.

SIGNIFICANCE AND IMPACT OF THE STUDY

The lactic acid bacteria obtained from plants in this study may be applicable for use in the dairy product industry.

Discrepancies between the phenotypic and genotypic characterization of Lactococcus lactis cheese isolates

AIMS

The use of randomly amplified polymorphic DNA (RAPD)-PCR fingerprinting and plasmid profiles to determine at the strain level, the similarity of Lactococcus lactis isolates obtained during sampling of traditional cheeses and to verify its correspondence to the selected phenotypic characteristics.

METHODS AND RESULTS

A total of 45 L. lactis isolates were genotypically analysed by RAPD-PCR fingerprinting and plasmid patterns. Phenotypic traits used to compare strains were proteolytic, acidifying, aminotransferase (aromatic and branched chain aminotransferase) and alpha-ketoisovalerate decarboxylase (Kivd) activities. The results show that 23 isolates could be grouped in clusters that exhibited 100% identity in both their RAPD and plasmid patterns, indicating the probable isolation of dominant strains during the cheese sampling process. However, there were phenotypic differences between isolates within the same cluster that included the loss of relevant technological properties such as proteinase activity and acidifying capacity or high variation in their amino acid converting enzyme activities. Likewise, the analysis of a specific attribute, Kivd activity, indicated that 7 of 15 isolates showed no detectable activity despite the presence of the encoding (kivd) gene.

CONCLUSION

Phenotypic differences found between genotypically similar strains of L. lactis strains could be linked to differences in enzymatic expression.

SIGNIFICANCE AND IMPACT OF THE STUDY

Phenotypic analysis of L. lactis isolates should be considered when selecting strains with new cheese flavour forming capabilities.

Shunt infection: is there a near-miss scenario?

OBJECT

The aim of this study was to establish whether microbiological contamination at the time of shunt insertion can be detected and used to predict the likelihood of subsequent shunt infection.

METHODS

A prospective study of pediatric patients undergoing primary shunt insertion was undertaken. Following the protocol devised for this study, three swab samples were collected from the surgical wounds during each procedure. These samples were incubated and subcultured, and the isolates were identified and stored. In patients who subsequently presented with clinical evidence of shunt infection, cerebrospinal fluid (CSF) was analyzed using microscopy, tissue cultures, and sensitivity testing. The organisms isolated at the time of shunt insertion and those responsible for subsequent shunt infection were then compared. The study population consisted of 107 pediatric patients. Because one patient underwent placement of an additional contralateral shunt system, there were 108 total shunt insertions yielding 325 swab samples. Organisms were identified in cultures of 50 swab samples (15%) obtained in 40 patients (37%). In seven of these 40 patients (17.5%) a CSF infection subsequently developed. In only one patient was the infectious organism the same as that isolated from the swab specimens. In an additional six patients (8.8%) a CSF infection occurred despite the lack of growth in the cultures from intraoperative swab samples.

CONCLUSIONS

The organisms responsible for shunt infection were rarely detected in the operative wound at the time of shunt insertion, leading the authors to conclude that the vulnerable period for bacterial colonization of shunts may not be restricted to the operative procedure as is commonly believed, but may extend throughout the postoperative period of wound healing. These findings have implications not only for a better understanding of the cause of shunt infections but also for the development of strategies to prevent them.

Endocarditis caused by Lactococcus lactis subsp. lactis in a patient with atrial myxoma: a case report

We report a case of subacute endocarditis in a 55-year-old patient affected by left atrial myxoma and with a severe mitral regurgitation. Lactococcus lactis subsp. lactis was isolated from blood cultures and infection was eliminated by treatment with amoxicillin-clavulanic acid.

Plasmid content and bacteriocin production by five strains ofLactococcus lactisisolated from semi-hard homemade cheese

In this study, the plasmid content and bacteriocin production of natural isolates of lactococci were investigated. Five bacteriocin producing lactococcal strains (Lactococcus lactis subsp. lactis BGMN1-2, BGMN1-3, BGMN1-5, BGMN1-6, and BGMN2-7) were isolated as nonstarter microflora of semi-hard homemade cheese and characterized. All isolates contained a number of plasmids. It was shown that lcnB structural genes for bacteriocin lactococcin B were located on large plasmids in all isolates. In the strains BGMN1-3 and BGMN1-5 proteinase prtP genes collocated with lcnB. Furthermore, these strains produced two additional bacteriocins (LsbA and LsbB) with genes responsible for their production and immunity located on the small rolling circle-replicating plasmid pMN5. Using deletion experiments of pMN5, minimal replicon of the plasmid and involvement of a bacteriocin locus in plasmid maintenance were identified. In addition, plasmid curing experiments showed that genes for catabolism or transport of 10 carbohydrates in the strain BGMN1-5 were plasmid located.Key words: lactococci, natural isolates, bacteriocin, plasmid curing.

Yoghurt consumption and damaged colonic mucosa: a case of Lactococcus lactis liver abscess in an immunocompetent patient

Lactococcus lactis is an uncommon cause of invasive disease in humans. We present a case of L. lactis liver abscess in an immunocompetent adult, apparently related to consumption of live culture yoghurt.

Ubiquity and diversity of multidrug resistance genes inLactococcus lactisstrains isolated between 1936 and 1995

The presence and the nucleotide sequence of four multidrug resistance genes, lmrA, lmrP, lmrC, and lmrD, were investigated in 13 strains of Lactococcus lactis ssp. lactis, four strains of Lactococcus lactis ssp. cremoris, two strains of Lactococcus plantarum, and two strains of Lactococcus raffinolactis. Multidrug resistance genes were present in all L. lactis isolates tested. However, none of them could be detected in the strains belonging to the species L. raffinolactis and L. plantarum, suggesting a different set of multidrug resistance genes in these species. The analysis of the four deduced amino acid sequences established two different variants depending on the subspecies of L. lactis. Either lmrA, or lmrP, or both were found naturally disrupted in five strains, while full-length lmrD was present in all strains.

[Isolation and identification of new nisin-producing Lactococcus lactis subsp. lactis from milk]

A method for isolating active nisin-producing strains of mesophilic lactococci was developed. Overall, 55 strains of mesophilic lactic acid bacteria were isolated from fresh cow's milk obtained from milk farms in various regions throughout Russia; of them, 36 displayed nisin-synthesizing activity. The three most active strains were studied according to morphological, cultural, physiological, and biochemical characteristics and identified as Lactococcus lactis subsp. lactis. The species attribution of the strains studied was confirmed by the similarity of the nucleotide sequences of the 16S rRNA gene. The nucleotide sequences of the 16S rRNA genes were deposited with the GenBank under accession numbers DQ255951-DQ255954. The distinctions between these strains in physiological and biochemical characteristics and the ranges of their bactericide action on the microorganisms capable of developing in agricultural materials and food products were determined. The isolated strains displayed considerably wider ranges of action, which differed from the nisin-producing strain MGU and the commercial nisin preparation (Nisaplin), used as a biological preserving agent.

Use of real time PCR to determine population profiles of individual species of lactic acid bacteria in alfalfa silage and stored corn stover

Real-time polymerase chain reaction (RT-PCR) was used to quantify seven species of lactic acid bacteria (LAB) in alfalfa silage prepared in the presence or absence of four commercial inoculants and in uninoculated corn stover harvested and stored under a variety of field conditions. Species-specific PCR primers were designed based on recA gene sequences. Commercial inoculants improved the quality of alfalfa silage, but species corresponding to those in the inoculants displayed variations in persistence over the next 96 h. Lactobacillus brevis was the most abundant LAB (12 to 32% of total sample DNA) in all of the alfalfa silages by 96 h. Modest populations (up to 10%) of Lactobacillus plantarum were also observed in inoculated silages. Pediococcus pentosaceus populations increased over time but did not exceed 2% of the total. Small populations (0.1 to 1%) of Lactobacillus buchneri and Lactococcus lactis were observed in all silages, while Lactobacillus pentosus and Enterococcus faecium were near or below detection limits. Corn stover generally displayed higher populations of L. plantarum and L. brevis and lower populations of other LAB species. The data illustrate the utility of RT-PCR for quantifying individual species of LAB in conserved forages prepared under a wide variety of conditions.

Microbial diversity and succession during the manufacture and ripening of traditional, Spanish, blue-veined Cabrales cheese, as determined by PCR-DGGE

The diversity and dynamics of the dominant microbial communities arising during the manufacture and ripening of four batches of naturally fermented Cabrales cheese were investigated by the PCR-DGGE culture-independent technique. Total microbial DNA was extracted from cheese milk, curd and cheese samples and used as template material in PCR experiments to amplify the V3 region of the bacterial 16S rRNA gene, plus the D1 region of the eukaryotic 26S rRNA gene. These regions were then analysed using DGGE. Eukaryotic and bacterial bands were identified by isolation, reamplification and sequencing. The results were compared to those obtained in a previous microbial characterization of the same four batches using classical culturing methods. Great variability was recorded between batches by the PCR-DGGE technique. This was also shown by culturing, and underlines the uniqueness of artisanal products. Lactocococcus lactis subsp. lactis was dominant from the cheese milk stage until the end of ripening, whereas populations of certain Lactobacillus species appeared during ripening. Populations of species never isolated by culturing were found to be numerous by the PCR-DGGE method, in particular Lactococcus garvieae and Lactococcus raffinolactis. Other, completely unknown lactococci were also detected. The dominant eukaryotic populations from day 15 onwards were those of Penicillium roqueforti and Geotrichum candidum.

Portal vein thrombosis and liver abscess due to Lactococcus lactis

A 26-year-old man was admitted with fever and abdominal pain. Abdominal ultrasonography and Doppler ultrasound eventually revealed portal vein thrombosis and a pyogenic liver abscess (17x11x11 cm). Lactococcus lactis was isolated from a culture of the abscess material. This organism is not a common pathogen in humans. This is the first published description of portal vein thrombosis and pyogenic liver abscess due to L. lactis.

[Screening, isolation and identification of nisin resistance determinant gene in strains of Lactococcus lactis]

OBJECTIVE

To isolate and identify nisin resistance determinant (NSR) gene from Lactococcus lactis.

METHODS

The Lactococcus lactis strains harboring NSR gene were isolated from different milk samples by selective culture supplemented with nisin and confirmed by PCR detection of 16S rRNA. Nisin resistance determinant gene was determined by PCR amplification, enzyme digestion and sequencing.

RESULTS

Thirty nisin-resistant Lactococcus lactis strains from fresh milk samples were obtained. Three of these strains contained NSR gene of about 1000 bp as determined by agarose gel electrophoresis and further confirmed by enzyme digestion and sequence analysis. The NSR gene was located on the plasmid of Lactococcus lactis.

CONCLUSION

Complete NSR gene, located on the bacterial plasmid, has been successfully isolated from nisin-resistant Lactococcus lactis strains from fresh milk.

Characterization of bacteriocin HV219, produced byLactococcus lactis subsp.lactis HV219 isolated from human vaginal secretions

Bacteriocin HV219, produced by Lactococcus lactis subsp. lactis HV219, is active against Gram-positive and Gram-negative bacteria. Activity was lost when treated with proteolytic enzymes, SDS, Triton X-114 and Triton X-100, but not at pH 2.0 to 10.0 or after 20 min at 121 degrees C. Growth in the presence of yeast extract as sole nitrogen source yielded 3200 AU/ml. No bacHV219 activity was recorded in MRS broth with maltose, mannose, lactose or sucrose as sole carbohydrate, but fructose yielded 1600 AU/ml. K(2)HPO(4) at 10.0 g/l yielded 3200 AU/ml. Addition of 1.0 mg/l cyanocobalamin, l-ascorbic acid and thiamine to MRS broth yielded 3200 AU/ml, 1600 AU/ml and 1600 AU/ml, respectively. The mode of activity is bacteriolytic, as confirmed by atomic force microscopy.

Lactococcin Q, a novel two-peptide bacteriocin produced by Lactococcus lactis QU 4

A bacteriocin-producing strain, Lactococcus lactis QU 4, was isolated from corn. The bacteriocin, termed lactococcin Q, showed antibacterial activity only against L. lactis strains among a wide range of gram-positive indicator strains tested. Lactococcin Q was purified by acetone precipitation, cation exchange chromatography, and reverse-phase chromatography. Lactococcin Q consisted of two peptides, alpha and beta, whose molecular masses were determined to be 4,260.43 Da and 4,018.36 Da, respectively. Amino acid and DNA sequencing analyses revealed that lactococcin Q was a novel two-peptide bacteriocin, homologous to lactococcin G. Comparative study using chemically synthesized lactococcin Q (Qalpha plus Qbeta) and lactococcin G (Galpha plus Gbeta) clarified that hybrid combinations (Qalpha plus Gbeta and Galpha plus Qbeta) as well as original combinations showed antibacterial activity, although each single peptide showed no significant activity. These four pairs of lactococcin peptides acted synergistically at a 1:1 molar ratio and exhibited identical antibacterial spectra but differed in MIC. The MIC of Qalpha plus Gbeta was 32 times higher than that of Qalpha plus Qbeta, suggesting that the difference in beta peptides was important for the intensity of antibacterial activity.

Natural diversity and adaptive responses of Lactococcus lactis

Lactococcus lactis is the primary model organism for lactic acid bacteria (LAB) and is widely used in the production of fermented dairy products. In recent years there has been increasing interest in strains isolated from non-dairy environments, as these exhibit a high metabolic diversity and have unique flavour-forming activities. Recent progress has been made in understanding the natural diversity and adaptive responses of L. lactis from dairy and non-dairy origins. Genome sequencing and comparative genomics have also had an impact on understanding natural diversity within the species, and have provided new opportunities for industrial strain development.

Evaluation of microbial diversity during the manufacture of Fior di Latte di Agerola, a traditional raw milk pasta-filata cheese of the Naples area

Microbial diversity of the raw milk for the production of Fior di Latte di Agerola and its changes during cheesemaking were studied. Viable counts showed that at the end of curd ripening, loads of lactic acid bacteria, both mesophilic and thermophilic rods and cocci, higher than those commonly evidenced in similar cheeses produced by using natural or commercial starters, were detected. Identification of 272 isolates, supported by molecular diagnostic aids, evidenced representative cultures of a high number of bacterial taxa of interest as participating in the process, although most of the isolates belonged to Lactococcus lactis and Lactobacillus helveticus species. RAPD-PCR and REA-PFGE biotyping were performed for the isolates of the above species and it was shown that most of the strains isolated from the raw milk occurred during the whole cheesemaking process, and an active role of these strains in the fermentation was supposed. The results offer further proof of the importance of the raw milk as source of technologically interesting strains of lactic acid bacteria capable of driving the fermentation of traditional cheeses.

Isolation and characterization of promoters from Lactococcus lactis ssp. cremoris LM0230

DNA fragments showing promoter activity were obtained from the chromosomal DNA of Lactococcus lactis ssp. cremoris LM0230 by using a promoter-screening vector pBV5030, which contains a promoterless chloramphenicol acetyltransferase gene. Ten fragments were identified based on their ability to confer resistance against chloramphenicol in Escherichia coli. DNA sequencing revealed that all the fragments had a consensus region recognized by the sigma factor and only the nucleotide sequence of fragment 15C had the identical consensus region with the promoter P2 from L. lactis ssp. lactis MG1614. To compare their promoter strengths, an E. coli-lactococcal shuttle vector pWL1 containing a luciferase gene as the reporter gene was constructed based on lactococcal plasmid pMG36e. The putative promoter regions of 10 fragments exhibiting promoter activity were characterized in E. coli and L. lactis by measuring the luciferase activity, among which the putative promoter P6C exhibited the highest promoter activity both in E. coli JM109 and L. lactis ssp. cremoris MG1363. The luciferase system endowed significantly different expression levels enough to compare promoter strengths in E. coli and lactococcal host. The transcription-initiation sites of P6C and P13C were mapped by primer extension, which showed that they corresponded to a purine residue. The characterized promoters could be useful for the industrial production of heterologous proteins in L. lactis in case the proteins require a high safety level.

Use of hydrolysates from Atlantic cod (Gadus morhua L.) viscera as a complex nitrogen source for lactic acid bacteria

Hydrolysates of cod viscera were tested as an alternative to commonly used complex nitrogen sources (peptones and/or extracts) for the type strains of the lactic acid bacteria Lactococcus lactis, Lactobacillus acidophilus, Lactobacillus helveticus, Lactobacillus casei, Lactobacillus sakei and Pediococcus pentosaceus. Comparative studies with MRS-like media containing different nitrogen sources showed that all the fish hydrolysates performed equally well or better than commercial extracts/peptones for all selected lactic acid bacteria.