Genera Of Lactic Acid Bacteria Research Articles

Phenotypic and genotypic characterization of antimicrobial resistances reveals the effect of the production chain in reducing resistant lactic acid bacteria in an artisanal raw ewe milk PDO cheese

Antimicrobial resistance (AMR) is a significant public health threat, with the food production chain, and, specifically, fermented products, as a potential vehicle for dissemination. However, information about dairy products, especially raw ewe milk cheeses, is limited. The present study analysed, for the first time, the occurrence of AMRs related to lactic acid bacteria (LAB) along a raw ewe milk cheese production chain for the most common antimicrobial agents used on farms (dihydrostreptomycin, benzylpenicillin, amoxicillin and polymyxin B). More than 200 LAB isolates were obtained and identified by Sanger sequencing (V1-V3 16S rRNA regions); these isolates included 8 LAB genera and 21 species. Significant differences in LAB composition were observed throughout the production chain (P ≤ 0.001), with Enterococcus (e.g., E. hirae and E. faecalis) and Bacillus (e.g., B. thuringiensis and B. cereus) predominating in ovine faeces and raw ewe milk, respectively, along with Lactococcus (L. lactis) in whey and fresh cheeses, while Lactobacillus and Lacticaseibacillus species (e.g., Lactobacillus sp. and L. paracasei) prevailed in ripened cheeses. Phenotypically, by broth microdilution, Lactococcus, Enterococcus and Bacillus species presented the greatest resistance rates (on average, 78.2 %, 56.8 % and 53.4 %, respectively), specifically against polymyxin B, and were more susceptible to dihydrostreptomycin. Conversely, Lacticaseibacillus and Lactobacillus were more susceptible to all antimicrobials tested (31.4 % and 39.1 %, respectively). Thus, resistance patterns and multidrug resistance were reduced along the production chain (P ≤ 0.05). Genotypically, through HT-qPCR, 31 antimicrobial resistance genes (ARGs) and 6 mobile genetic elements (MGEs) were detected, predominating Str, StrB and aadA-01, related to aminoglycoside resistance, and the transposons tnpA-02 and tnpA-01. In general, a significant reduction in ARGs and MGEs abundances was also observed throughout the production chain (P ≤ 0.001). The current findings indicate that LAB dynamics throughout the raw ewe milk cheese production chain facilitated a reduction in AMRs, which has not been reported to date.

Detection of the lactic acid bacterial community in small scale white cheese processing facility using shotgun metagenomics and culturomics

This study aims to characterize lactic acid bacteria (LAB) community in small-scale white cheese processing facility highly favored by consumers. Shotgun metagenomics and culturomics based on MALDI-TOF MS approaches were employed. Samples from various production stages and equipment surfaces were collected. Dominant phyla in dairy and equipment samples were Firmicutes (63–70%) and Proteobacteria (84–89%), respectively. Lactococcus was the most abundant LAB genus across all samples, with Lactococcus lactis as dominant species followed by Streptococcus, Enterococcus, and Lactobacillus, indicating LAB community diversity contributing to product characteristics. Culturomics identified 12 LAB species, including Enterococcus faecalis and Lactobacillus delbrueckii. Metagenomics provided insights into microbial composition and dynamics in dairy environment, while culturomics identified specific LAB species. The combined approach offers a comprehensive view of dairy microbial communities, aiding industrial development by informing starter culture combinations for improved dairy products and processes.

Identification, Viability, and Membrane Potential during the Cryopreservation of Autochthonous Lactic-Acid Bacteria Isolated from Artisanal Adobera Cheese from Los Altos de Jalisco

Lactic acid bacteria (LAB) comprise a group of microorganisms responsible for developing the sensory and chemical characteristics of several foods and fermented products, particularly cheese. For this reason, after isolation and identification of LAB, validated protocols and procedures for their long-term preservation without compromising its integrity and technological properties, as well as methodologies aiming to assess their viability and integrity are paramount. This study aimed to isolate and identify autochthonous LAB from artisanal Adobera cheese and determine the effect of LAB cryopreservation with thioglycolate broth and glycerol on their viability, membrane integrity, and kinetics. Sixteen LAB were isolated and genetically identified from artisanal cheese samples; eleven of those strains were selected (genus Lactobacillus, Leuconostoc, Streptococcus, and Lactococcus) and included in the cryo-preservation assay. The initial average concentration of the bacterial suspensions was 6.89 log10 CFU mL−1; increasing to 8.9 log10 CFU mL−1 21 days later and slightly reduced at day 42 post-preservation (losses below one logarithm). About 77% of the cells maintained their membrane potential 180 days after their preservation and showed normal Kinetic parameters, maintaining normal adaptation times (Lag phase) and Log phases (9 h average), before reaching the stationary phase. The proposed protocol constitutes a viable alternative to the long-term preservation of different LAB genera because it keeps their viability and integrity. Using flow cytometry allowed the enumeration of viable LAB and provide evidence of the integrity of their membrane.

Characterization of Bacteriophage cd2, a Siphophage Infecting Carnobacterium divergens and a Representative Species of a New Genus of Phage.

Carnobacterium divergens is frequently isolated from natural environments and is a predominant species found in refrigerated foods, particularly meat, seafood, and dairy. While there is substantial interest in using C. divergens as biopreservatives and/or probiotics, some strains are known to be fish pathogens, and the uncontrolled growth of C. divergens has been associated with food spoilage. Bacteriophages offer a selective approach to identify and control the growth of bacteria; however, to date, few phages targeting C. divergens have been reported. In this study, we characterize bacteriophage cd2, which we recently isolated from minced beef. A detailed host range study reveals that phage cd2 infects certain phylogenetic groups of C. divergens. This phage has a latent period of 60 min and a burst size of ~28 PFU/infected cell. The phage was found to be acid and heat sensitive, with a complete loss of phage activity when stored at pH 2 or heated to 60°C. Electron microscopy shows that phage cd2 is a siphophage, and while it shares the B3 morphotype with a unique cluster of Listeria and Enterococcus phages, a comparison of genomes reveals that phage cd2 comprises a new genus of phage, which we have termed as Carnodivirus. IMPORTANCE Currently, very little is known about phages that infect carnobacteria, an important genus of lactic acid bacteria with both beneficial and detrimental effects in the food and aquaculture industries. This report provides a detailed characterization of phage cd2, a novel siphophage that targets Carnobacterium divergens, and sets the groundwork for understanding the biology of these phages and their potential use in the detection and biocontrol of C. divergens isolates.

Wild-type Lactococcus lactis producing bacteriocin-like prophage lysins.

Lactococcus is a genus of lactic acid bacteria used in the dairy industry as a starter. Lactococci have been found to produce altogether more than 40 different bacteriocins, ribosomally synthesized antimicrobial proteins. All known Lactococcus spp. bacteriocins belong to classes I and II, which are mainly heat-resistant peptides. No class III bacteriocins, bigger heat-sensitive proteins, including phage tail-like bacteriocins, have been found from the Lactococcus spp. Unlike phage tail-like bacteriocins, prophage lysins have not been regarded as bacteriocins, possibly because phage lysins contribute to autolysis, degrading the host's own cell wall. Wild-type Lactococcus lactis strain LAC460, isolated from spontaneously fermented idli batter, was examined for its antimicrobial activity. We sequenced the genome, searched phage lysins from the culture supernatant, and created knock-out mutants to find out the source of the antimicrobial activity. The strain LAC460 was shown to kill other Lactococcus strains with protease- and heat-sensitive lytic activity. Three phage lysins were identified in the culture supernatant. The genes encoding the three lysins were localized in different prophage regions in the chromosome. By knock-out mutants, two of the lysins, namely LysL and LysP, were demonstrated to be responsible for the antimicrobial activity. The strain LAC460 was found to be resistant to the lytic action of its own culture supernatant, and as a consequence, the phage lysins could behave like bacteriocins targeting and killing other closely related bacteria. Hence, similar to phage tail-like bacteriocins, phage lysin-like bacteriocins could be regarded as a novel type of class III bacteriocins.

Membrane lipid composition of Carnobacterium maltaromaticum CNCM I-3298, a highly cryoresistant lactic bacterium

The growing consumption of fermented products has led to an increasing demand for lactic acid bacteria (LAB), especially for LAB tolerant to freezing/thawing conditions. Carnobacterium maltaromaticum is a psychrotrophic and freeze-thawing resistant lactic acid bacterium. The membrane is the primary site of damage during the cryo-preservation process and requires modulation to improve cryoresistance. However, knowledge about the membrane structure of this LAB genus is limited. We presented here the first study of the membrane lipid composition of C. maltaromaticum CNCM I-3298 including the polar heads and the fatty acid compositions of each lipid family (neutral lipids, glycolipids, phospholipids). The strain CNCM I-3298 is principally composed of glycolipids (32%) and phospholipids (55%). About 95% of glycolipids are dihexaosyldiglycerides while less than 5% are monohexaosyldiglycerides. The disaccharide chain of dihexaosyldiglycerides is composed of α-Gal(1−2)-α-Glc chain, evidenced for the first time in a LAB strain other than Lactobacillus strains. Phosphatidylglycerol is the main phospholipid (94%). All polar lipids are exceptionally rich in C18:1 (from 70% to 80%). Regarding the fatty acid composition, C. maltaromaticum CNCM I-3298 is an atypical bacterium within the genus Carnobacterium due to its high C18:1 proportion but resemble the other Carnobacterium strains as they mostly do not contain cyclic fatty acids.

NMR-Based Metabolomic Study on Phaseolus vulgaris Flour Fermented by Lactic Acid Bacteria and Yeasts.

In recent years, fermented foods have attracted increasing attention due to their important role in the human diet, since they supply beneficial health effects, providing important sources of nutrients. In this respect, a comprehensive characterization of the metabolite content in fermented foods is required to achieve a complete vision of physiological, microbiological, and functional traits. In the present preliminary study, the NMR-based metabolomic approach combined with chemometrics has been applied, for the first time, to investigate the metabolite content of Phaseolus vulgaris flour fermented by different lactic acid bacteria (LAB) and yeasts. A differentiation of microorganisms (LAB and yeasts), LAB metabolism (homo- and heterofermentative hexose fermentation), LAB genus (Lactobacillus, Leuconostoc, and Pediococcus), and novel genera (Lacticaseibacillus, Lactiplantibacillus, and Lentilactobacillus) was achieved. Moreover, our findings showed an increase of free amino acids and bioactive molecules, such as GABA, and a degradation of anti-nutritional compounds, such as raffinose and stachyose, confirming the beneficial effects of fermentation processes and the potential use of fermented flours in the production of healthy baking foods. Finally, among all microorganisms considered, the Lactiplantibacillus plantarum species was found to be the most effective in fermenting bean flour, as a larger amount of free amino acids were assessed in their analysis, denoting more intensive proteolytic activity.

Probiotic and technological characterization of selected Lactobacillus strains isolated from different egyptian cheeses

BackgroundFresh milk and natural environmental conditions are used to produce traditional cheeses. Such cheeses are produced by dozens of different types of microbes. Non-starter lactobacilli are the most responsible genus of lactic acid bacteria exhibiting key technological and health promoting traits. The purpose of this study is to isolate Lactobacillus bacteria from conventional Egyptian cheeses and analyse their probiotic potential and technological properties.ResultsLactobacillus isolates (33 isolates) were isolated from different Egyptian cheeses. Our results revealed that 18.18% of the isolates were fast-acidifying, 30.3% were medium-acidifying and 51.5% were slow-acidifying isolates. The results of autolytic activity showed that 24.3% of the isolates were good autolysis, 33.3% were fair autolysis, while 42.4% were poor autolysis. Fifteen isolates produced exopolysaccharides, while 9 isolates exhibited antimicrobial activities against Lactobacillus bulgaricus 340. All the isolates were resistant to pH 3 for 3 h except isolate No. 15 (MR4). The growth rate of the isolates ranged from 42.25 to 85.25% at 0.3% bile salts after 3 h of incubation. The surviving percentage of the Lactobacillus isolates decreased with increasing incubation time or the percentage of bile salts greater than 0.3%. All the isolates grew after incubation in artificial gastric and intestinal fluids. The auto-aggregation of 15 isolates ranged from 43.13 to 72.77%. Lacticaseibacillus paracasei BD3, Lactiplantibacillus plantarum BR4 and Limosilactobacillus fermentum MR2 were sensitive to the majority of the tested antibiotics and showed good bile salt hydrolase activity.ConclusionL. paracasei BD3, L. plantarum BR4 and L. fermentum MR2 were isolated from Egyptian cheeses and showed probiotic and technological characterization, which are valuable for their practical application as starters, adjunct and protective cultures in cheese making.

Investigation of lactic acid bacterial profiles in commercial rice wine and their effect on metabolites during low-temperature storage

Makgeolli, the traditional Korean rice wine, is generally considered to contain lactic acid bacteria (LAB) despite its bacterial inoculation-free brewing process. The existence of LAB in makgeolli often presents inconsistent trends in microbial profiles and cell numbers. Therefore, to establish LAB-related insights, 94 commercial non-pasteurized products were collected and microbial communities and metabolites were analyzed using 16S rRNA amplicon sequencing and GC–MS, respectively. All samples contained various LAB genera and species, with an average viable cell number of 5.61 log CFU/mL. Overall, 10 LAB genera and 25 LAB species were detected; the most abundant and frequent LAB genus was Lactobacillus. There was no significant change in the LAB composition profile or lactic acid content during low-temperature storage, indicating the presence of LAB did not significantly affect the quality of makgeolli under low-temperature storage conditions. Overall, this study contributes to understand the microbial profile and role of LAB in makgeolli.

Development and Applications of CRISPR/Cas9-Based Genome Editing in Lactobacillus

Lactobacillus, a genus of lactic acid bacteria, plays a crucial function in food production preservation, and probiotics. It is particularly important to develop new Lactobacillus strains with superior performance by gene editing. Currently, the identification of its functional genes and the mining of excellent functional genes mainly rely on the traditional gene homologous recombination technology. CRISPR/Cas9-based genome editing is a rapidly developing technology in recent years. It has been widely applied in mammalian cells, plants, yeast, and other eukaryotes, but less in prokaryotes, especially Lactobacillus. Compared with the traditional strain improvement methods, CRISPR/Cas9-based genome editing can greatly improve the accuracy of Lactobacillus target sites and achieve traceless genome modification. The strains obtained by this technology may even be more efficient than the traditional random mutation methods. This review examines the application and current issues of CRISPR/Cas9-based genome editing in Lactobacillus, as well as the development trend of CRISPR/Cas9-based genome editing in Lactobacillus. In addition, the fundamental mechanisms of CRISPR/Cas9-based genome editing are also presented and summarized.

Variations in fungal and bacterial microbiome and chemical composition among fermenting Kishu-Narezushi batches.

Kishu-Narezushi is a spontaneously fermented food comprising fish, rice, and salt. During spontaneous fermentation, the microbiome may differ among batches, even when manufactured in the same way. In addition, analyses of changes in the chemical composition of the product are important for clarifying flavor characteristics. We collected basic information on the microbiome and chemical composition of Kishu-Narezushi using multiple batches of fermentation and evaluated whether the microbiome was homogeneous. The fungal microbiome of Kishu-Narezushi was dominated by Saccharomycetales and Trichosporonales. The bacterial microbiome was diverse, although seven specific genera of lactic acid bacteria were identified. Glutamic acid, histidine, and serine levels decreased after ∼10 days of fermentation. Succinic acid, characteristic of Kishu-Narezushi, accumulated upon the consumption of glutamic acid. Though the microbiome was diverse, the chemical composition was similar among the batches.

Low-cost Media from Agro-industrial Wastes for the Cultivation and Metabolite Production of Lactic Acid Bacteria

Lactic acid bacteria (LAB) are the most well-documented, “generally regarded as safe” microorganisms used in food fermentation, cosmetics, and pharmaceuticals. Many probiotic strains are utilized for the production of beneficial metabolites, such as bacteriocins and lactic acid, which influence the preservation, organoleptic characteristics, and nutritional properties of food. However, these strains are usually cultured using complex and expensive media, which significantly contribute to the cost of the final product. Thus, this study aims to develop a low-cost alternative medium (LCAM) for the growth and metabolite production of industrially important LAB strains. After several preliminary experiments, an LCAM containing rice bran extract, waste coconut (mature) water, baker’s yeast extract, table sugar, and salts was subjected to a statistically-guided optimization study for growth support of a model LAB strain Lactobacillus plantarum BS. Based on the second-order response mathematical model, the optimized medium composition was 35% rice bran extract and 58% waste coconut water, 1% baker’s yeast extract, 1% table sugar, and 5% salt solution (LCAM A) plus a modified version without baker’s yeast and table sugar (LCAM B). Predicted values were acceptable at 95% (8.91 and 8.88 log CFU/mL) and highly comparable (102% relativity) with the commercial complex medium used as control. Both LCAM formulations were found to support the growth and metabolite production of different LAB genera (L. plantarum BS, Lactococcus lactis NCDO 497, Enterococcus faecalis M4-3, Streptococcus thermophilus BIOTECH 1555, and Pediococcus acidilactici BIOTECH 1068). The LCAM supported the metabolite production of these LAB strains comparable with the commercial medium but is 7.4–7.6-fold cheaper than the cheapest commercial medium. This significant cost reduction has a huge prospect on the large-scale utilization of LAB. Nevertheless, further studies are necessary to enhance the nutritive composition of LCAM for other genera of LAB.

Characterization of Microorganisms in Fish and Farmed Water from Sidi M’Hamed Ben Tiba Dam (Algeria)

Background: The production of fishery resources and the abundance of new species in our markets are becoming increasingly important. The consumption of fish continues to increase. Microbiological analysis of fish provides information on the diversity of the bacterial population abundant in these species. Methods: Our work was based on the isolation and identification of the bacterial flora of two fish species bred in extensive mode at the Sidi M’Hamed Ben Taiba dam (Barbel and Bighead carp). By introducing the influence environmental factors on the load and diversity of bacterial species by physicochemical (temperature, pH, turbidity, conductivity and dissolved oxygen) and bacteriological (search for total and faecal coliforms, enterococci and sulphate-reducing bacteria) analysis of the rearing water. Result: A variety of bacteria were isolated from the different compartments of the two fish species. Of which we were able to identify 12 species divided into 9 genera: Staphylococcus, Streptococcus, Pseudomomas, Serratia, Salmonella, Citrobacter, Proteus, Chrysobacterium, Stenotrophomonas and genera of lactic acid bacteria.

An Extensive Review on Production, Purification, and Bioactive Application of Different Classes of Bacteriocin

Lactic Acid Bacteria (LAB) synthesize various metabolites during their growth phase and are Generally Recognized as­­ Safe (GRAS) and Qualified Presumption of Safety (QPS). Ribosomally synthesized Antimicrobial Peptides (AMP) or Bacteriocins from the genera of Lactic Acid Bacteria and other prokaryotic genera are cationic, heat-stable, amphiphilic and the membrane permeabilizing peptides built with an excess amount of lysyl and arginyl residues. Antimicrobial compounds produced by LAB depend on the physical and biological conditions of microbial culture. Different classes of bacteriocin are produced by both Gram-positive and Gram-negative bacteria. The production of bacteriocin is influenced by various environmental factors. Bacteriocin has a wide variety of applications in various fields.   The application spectrum of bacteriocins can be expanded in various domains such as food processing, biomedical, and personal care due to the increase in the number of newly discovered bacteriocins. Bacteriocins acquire a wide spectrum of antimicrobial activity with minimal level of cytotoxicity. In addition, bacteriocins were studied for their anticancer activity against different cancer cell lines. Selective binding of bacteriocins (cationic) towards cancer cells (anionic) increases the cytotoxicity of cancer cells. Bacteriocin peptides initiate necrosis by communicating with the cell surface which selectively targets and kills the cells with tumor formation and does not cause any damage to the normal healthy cells. In this review, the bacteriocins synthesized from lactic acid bacteria along with their interaction with cancer cell lines and other applications are discussed along with a few examples of other bioactive compounds produced by LAB. 

Bifidobacterium lactis Inhibits iNOS Expression in LPS-stimulated RAW 264.7 Macrophages

BACKGROUND: Bifidobacterium is a genus of lactic acid bacteria that lives in the large intestine of humans and animals. The health benefits of this genus are well established; however, the anti-inflammatory activity of this genus, specifically Bifidobacterium lactis, has not been well defined. Therefore, in this study, we evaluated anti-inflammatory activity of B. lactis hydrolysates using lipopolysaccharide (LPS)-stimulated RAW 264.7 macrophages.METHODS: RAW 264.7 cells were cultured using Dulbecco’s Modified Eagle’s Medium in 5 % CO2 incubator at 37 ℃. One µg/mL of LPS was used to stimulate RAW 264.7 cells. Nitric oxide (NO) production, inducible nitric oxide synthase (iNOS), and cyclooxygenase-2 (COX-2) were measured to evaluate anti-inflammatory activity of B. lactis hydrolysates. The cytotoxicity of the inhibitor was also measured in present study through 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) assay.RESULTS: The results showed that B. lactis hydrolysates at 25–200 μg/mL inhibited NO production. In concentration-dependent manner, B. lactis hydrolysate showed inhibition of iNOS expression. However, no inhibition on COX-2 expression was observed. The MTS assay of the B. lactis hydrolysates showed no side effects on the cell viability at all concentrations.CONCLUSION: The current study revealed that B. lactis hydrolysates possess specific anti-inflammatory effects by inhibiting iNOS expression without cytotoxicity and therefore could potentially be developed as a new iNOS inhibitor.KEYWORDS: Bifidobacterium lactis, macrophages, hydrolysates, iNOS, COX-2

Comparative genomics analysis of genus Leuconostoc resolves its taxonomy and elucidates its biotechnological importance

Genus Leuconostoc consists of a diverse range of lactic acid bacteria (LAB) from dairy, food and environmental ecology. Even though the species of Leuconostoc are commercially significant, their taxonomy is largely based on old, low-resolution classical methods. Several taxonomic reclassifications in the past were inadequate for microbiologist and food industry professionals to demarcate any new strain of genus Leuconostoc. The current taxonomy of the genus is largely based on classical approaches, which are in utmost need of reinvestigation by whole genome-based approaches. In the present study, the taxono-phylogenomic analysis depicted sixteen species, including three novel genomospecies and several reshufflings across the species, namely, L. mesenteroides, L. pseudomesenteroides, L. gelidum and L. lactis. Genus-wide T3PKS, CAZymes, and vector plasmids supports its biotechnological potential. However, detection of the antibiotic resistance genes in such an important LAB genus raises concern over their utility in industry. Present, large-scale in-depth genome-based study can shed light on the genome dynamics of the member species, help to obtain a more robust taxonomy and elucidate its biotechnology importance.

GENOTYPIC AND PHENOTYPIC CHARACTERIZATION OF BACTERIOCINOGENIC LACTIC ACID BACTERIAL STRAINS FOR POSSIBLE BENEFICIAL, VIRULENCE, AND ANTIBIOTIC RESISTANCE TRAITS

Lactic acid bacteria (LAB) are a diverse group of microorganisms that can be found in natural habitats and are used in a wide range of industries, especially in the food sector. They are regarded "Generally Recognized as Safe" and are commonly used as a starter culture, probiotics, and biopreservative. However, some LAB genera are excluded from the "Qualified Presumption of Safety" (QPS) list due to the possibility that they have virulence and antibiotic resistance genetic determinants. The objective of this study was to investigate the beneficial, virulence, and antibiotic resistance-related genes in 10 well-characterized bacteriocinogenic LAB strains. The auto-aggregation, co-aggregation, cell surface hydrophobicity, and bile salt tolerance were also evaluated to examine their potential as bacteriocinogenic probiotics and/or starter culture. Results showed that all tested strains showed abilities for auto-aggregation at 4oC and 37oC, co-aggregation with S. aureus JCM8704, S. typhimurium BIOTECH1826, and E. coli DH5α, and significant cell-surface hydrophobicity. However, only a few strains were able to withstand the media treated with 0.3% bile salt. Among the tested bacteriocinogenic LAB strains, L. lactis IO-1 and C. divergens V41 had the maximum values for auto-aggregation at 4oC and 37oC, respectively. C. divergens V41 also exhibited the highest percentage for cell surface hydrophobicity. E. faecium NKR-5-3 showed the highest co-aggregation percentages with all indicator strains. Our findings also showed that the tested isolates presented distinct combinations of virulence-related genes. Only two of ten bacteriocinogenic LAB strains exhibited presence of multiple virulence genes. Lactococcus sp. QU12 was found to have a high frequency of beneficial and virulence genes, with 2 out of 7 genes present encoding beneficial factor and 11 out of 13 genes encoding virulence factor. Lactococcus sp. QU12 and L. lactis IO-1 were also positive for tetracycline resistance gene tetM and aminoglycoside resistance gene aphA-2, respectively, and transposon genes. Moreover, only a few LAB isolates tested positive for 2 out of 8 antibiotic resistance classes. Although few, the substantial danger of these genes being transferred and acquired cannot be overlooked as this could potentially cause serious health concerns in the future. These results suggest that despite the promising properties of bacteriocinogenic LAB, careful safety evaluation of these strains should be a prerequisite before using these in food systems.

Characterization of two new strains of Lactococcus lactis for their probiotic efficacy over commercial synbiotics consortia.

Lactococcus spp. are industrially crucial lactic acid bacteria (LAB) used to manufacture lactic acid, pickled vegetables, buttermilk, cheese, and many kinds of delicious dairy foods and drinks. In addition to these, they are also being used as probiotics in specific formulations. However, their uses as probiotics are comparatively less than the other LAB genera. The present communication hypothesizes to validate the probiotic potentiality of two new Lactococcus lactis subsp. lactisstrains for their future uses. These native food fermenting strains were characterized for in vitro acid tolerance, tolerance to simulated gastric and pancreaticjuices, autoaggregation and co-aggregation, hydrophobicity, haemolytic activity, bile salt deconjugation, cholesterol removal, antimicrobial spectrum, and antibiotic sensitivity. The in vivo live bacterial feeding of these strainsfor 30days was done in Swiss albino mice either singly or in combination with prebiotic inulin and evaluated for hypocholesterolemic activity, immune enhancement, and gut colonization efficiency and compared with the commercial probiotic consortia. The study revealed that the strains could survive in human gut bile concentration, gastric pH conditions at pH 2.0, 3.0, and 8.0 for 6h, had a broad antibacterial spectrum, and cholesterol binding efficacy. The strains could survive with higher colony-forming units (CFU/mL) when amended with sodium caseinate. The strains had autoaggregation ranges from 15 to 25% over 24h and had a significant co-aggregation with both lactic acid and Gram-positive and Gram-negative bacterial strains related to human illness. The strains also showed solvent and media-specific hydrophobicity against n-hexane and xylene. The live bacterial feeding either singly or in combination with prebiotic inulin resulted in a significant reduction of LDL (low-density lipoprotein), VLDL (very low-density lipoprotein) cholesterol and triglyceride (TG), and a significant increase in HDL (high-density lipoprotein) cholesterol level, and improved gut colonization and gut immunomodulation. The results prove that these non-haemolytic, non-toxic strains had significant health benefits than the commercial probiotics consortium with the recommended prebiotics mix. Thus, these new Lactococcus lactis subsp. lactis strains could be trialled as a new probiotic combination for human and animal feeds.

Role of the Mn-Catalase in Aerobic Growth of Lactobacillus plantarum ATCC 14431

Lactobacilli are Gram-positive aerotolerant organisms that comprise the largest genus of Lactic Acid Bacteria (LAB). Most lactobacilli are devoid of the antioxidant enzymes, superoxide dismutases, and catalases, required for protection against superoxide radicals and hydrogen peroxide (H2O2), respectively. However, some lactobacilli can accumulate millimolar concentrations of intracellular manganese and spare the need for superoxide dismutase, while others possess non-heme catalases. L. plantarum is associated with plant materials and plays an important role in fermented foods and gut microbiomes. Therefore, understanding the effects of the environment on the growth and survival of this organism is essential for its success in relevant industrial applications. In this report, we investigated the physiological role of Mn-catalase (MnKat) in Lactobacillus plantarum ATCC 14431. To this end, we compared the physiological and morphological properties of a ΔMnkat mutant strain and its isogenic parental strain L. plantarum ATCC 14431. Our data showed that the MnKat is critical for the growth of L. plantarum ATCC 14431 in the presence of oxygen and resistance to H2O2. The aerobic growth of the mutant in presence or absence of H2O2 was improved in the Mn-rich medium (APT) as compared to the growth in MRS medium. Furthermore, under aerobic conditions the mutant strain possessed atypical cellular morphology (i.e., shorter, and fatter). In conclusion, the MnKat of L. plantarum ATCC 14431 is important for aerobic growth, protection against H2O2, and maintenance of the rod-shaped cell morphology under aerobic conditions.

Metagenomics and volatile profile of Turkish artisanal Tulum cheese microbiota

Turkish artisanal Tulum cheese is a traditional raw milk cheese and starter cultures are not used for ripening process. In this study, 16S rRNA amplicon-based sequencing approach was used for determining bacterial diversity in Tulum cheeses. The volatile organic compound (VOC) profile which contributes to sensory properties of the cheeses was determined via solid-phase microextraction combined with gas chromatography-mass spectrometry (GC-MS/SPME) and correlated with the microbiota. In Tulum cheese samples, Lactobacillaceae (30,71%) phylum widely varied but Streptococcaceae (59,86%) was dominant. It mainly belongs to the four dominant genera of lactic acid bacteria (LAB) and includes Lactobacillus, Lactococcus, Streptococcus and Pediococcus. The bacterial diversity of TC5 sample was much higher than that of other samples. Moreover, several species of non-starter LAB were frequently detected. A total of 36 volatile compounds were identified including hydrocarbons (3), acids (13), alcohols (5), ketones (3), aldehydes (3), esters (8) and miscellaneous compound (1). Pentadecanoic acid, octadecanoic acid, tetradecanoic acid, octanoic acid, hexanoic acid were determined to be dominant in all cheese samples and to be related to microbial flora. Also, the sensory profiles of the samples were examined. The most popular TC6 did not contain 2-butanone and hexanal from the volatile organic compound (VOC) values, while in the most unpopular TC3, 2-butanone (7.73%) and hexanal (5.95%) were found to be the highest. The outcome of this study will contribute to literature on bacterial diversity and aromatic profile of Tulum cheese which should be investigated in order to improve quality and safety.