Leuconostoc strains isolated from dairy products: Response against food stress conditions

Phenotypic and genotypic antimicrobial resistance patterns in honey bee (Apis mellifera L.) bacterial symbionts

Antimicrobial resistance (AMR) is a major global public health problem. Nevertheless, the knowledge of the factors driving the spread of resistance among environmental microorganisms is limited, and few studies have been performed worldwide. Honey bees (Apis mellifera L.) have long been considered bioindicators of environmental pollution and more recently also of AMR. In this study, 53 bacterial strains isolated from the body surface of honey bees at three ontogenetic stages, collected from ten different geographic locations, were tested for their phenotypic and genotypic resistance to eight classes of the most widely used antimicrobials in human and veterinary medicine. Results showed that 83% of the strains were resistant to at least one antimicrobial and 62% were multidrug-resistant bacteria, with a prevalence of resistance to nalidixic acid, cefotaxime, and aztreonam. A high percentage of isolates harbouring at least one antimicrobial gene was also observed (85%). The gene encoding resistance to colistin mcr-1 was the most abundant, followed by those for tetracycline tetM and tetC. Geographical features influenced the distribution of these traits more than bacterial species or bee stage, supporting the use of honey bee colonies and their associated bacteria as indicators to monitor environmental resistance. This approach can improve the scientific understanding of this global threat by increasing data collection capacity.

Probiogenomics of Leuconostoc Mesenteroides Strains F-21 and F-22 Isolated from Human Breast Milk Reveal Beneficial Properties

Bacteria of the Leuconostoc genus are Gram-positive bacteria that are commonly found in raw milk and persist in fermented dairy products and plant food. Studies have already explored the probiotic potential of L. mesenteroides, but not from a probiogenomic perspective, which aims to explore the molecular features responsible for their phenotypes. In the present work, probiogenomic approaches were applied in strains F-21 and F-22 of L. mesenteroides isolated from human milk to assess their biosafety at the molecular level and to correlate molecular features with their potential probiotic characteristics. The complete genome of strain F-22 is 1.99 Mb and presents one plasmid, while the draft genome of strain F-21 is 1.89 Mb and presents four plasmids. A high percentage of average nucleotide identity among other genomes of L. mesenteroides (≥ 96%) corroborated the previous taxonomic classification of these isolates. Genomic regions that influence the probiotic properties were identified and annotated. Both strains exhibited wide genome plasticity, cell adhesion ability, proteolytic activity, proinflammatory and immunomodulation capacity through interaction with TLR-NF-κB and TLR-MAPK pathway components, and no antimicrobial resistance, denoting their potential to be candidate probiotics. Further, the strains showed bacteriocin production potential and the presence of acid, thermal, osmotic, and bile salt resistance genes, indicating their ability to survive under gastrointestinal stress. Taken together, our results suggest that L. mesenteroides F-21 and F-22 are promising candidates for probiotics in the food and pharmaceutical industries.

The Effect of Respiration, pH, and Citrate Co-Metabolism on the Growth, Metabolite Production and Enzymatic Activities of Leuconostoc mesenteroides subsp. cremoris E30

Leuconostoc mesenteroides includes strains used as starter and/or adjunct cultures for the production of several fermented foods. In this study, the effect of anaerobic and respiratory cultivations, as well as of citrate supplementation and different pH values, was evaluated on growth, biomass, metabolite, and enzymatic activities (pyruvate oxidase, POX; NADH-dependent oxidase, NOX; NADH-dependent peroxidase, NPR) of Leuconostoc mesenteroides subsp. cremoris E30. We compared the respiration-increased growth rate and biomass production of Leuc. mesenteroides E30 to anaerobic cultivation. A supplementation of citrate impaired the growth rate of the respiratory cells. As expected, anaerobic cultures did not consume oxygen, and a similar trend in oxygen uptake was observed in respiratory cultures. The aerobic incubation caused changes in the metabolic pattern, reducing the production of ethanol in favour of acetic acid. Citrate was already exhausted in the exponential phase and did not affect the yields in acetic acid and ethanol. NOX activity increased in the presence of oxygen, while catalase was also detected in the absence of hemin. The absence of H₂O₂ suggested its degradation by NPR and catalase. Respiratory cultivation provided benefits (increase in growth rate, biomass, and activity in antioxidant enzymes) for Leuc. mesenteroides E30. Therefore, the exploitation of respiratory phenotypes may be useful for the formulation of competitive starter or adjunct cultures.

Phenotypic Traits and Immunomodulatory Properties of Leuconostoc carnosum Isolated From Meat Products

Twelve strains of Leuconostoc carnosum from meat products were investigated in terms of biochemical, physiological, and functional properties. The spectrum of sugars fermented by L. carnosum strains was limited to few mono- and disaccharides, consistently with the natural habitats of the species, including meat and fermented vegetables. The strains were able to grow from 4 to 37°C with an optimum of approximately 32.5°C. The ability to grow at temperatures compatible with refrigeration and in presence of up to 60 g/L NaCl explains the high loads of L. carnosum frequently described in many meat-based products. Six strains produced exopolysaccharides, causing a ropy phenotype of colonies, according to the potential involvement on L. carnosum in the appearance of slime in packed meat products. On the other side, the study provides evidence of a potential protective role of L. carnosum WC0321 and L. carnosum WC0323 against Listeria monocytogenes, consistently with the presence in these strains of the genes encoding leucocin B. Some meat-based products intended to be consumed without cooking may harbor up to 10⁸ CFU/g of L. carnosum; therefore, we investigated the potential impact of this load on health. No strains survived the treatment with simulated gastric juice. Three selected strains were challenged for the capability to colonize a mouse model and their immunomodulatory properties were investigated. The strains did not colonize the intestine of mice during 10 days of daily dietary administration. Intriguingly, despite the loss of viability during the gastrointestinal transit, the strains exhibited different immunomodulatory effect on the maturation of dendritic cells in vivo, the extent of which correlated to the production of exopolysaccharides. The ability to stimulate the mucosal associated immune system in such probiotic-like manner, the general absence of antibiotic resistance genes, and the lack of the biosynthetic pathways for biogenic amines should reassure on the safety of this species, with potential for exploitation of selected starters.

Production Optimization, Structural Analysis, and Prebiotic- and Anti-Inflammatory Effects of Gluco-Oligosaccharides Produced by Leuconostoc lactis SBC001

Leuconostoc lactis SBC001, isolated from chive, produces glucansucrase and synthesizes oligosaccharides through its enzymatic activity. This study was conducted to optimize oligosaccharide production using response surface methodology, analyze the structure of purified oligosaccharides, and investigate the prebiotic effect on 24 bacterial and yeast strains and the anti-inflammatory activity using RAW 264.7 macrophage cells. The optimal conditions for oligosaccharide production were a culture temperature of 30 °C and sucrose and maltose concentrations of 9.6% and 7.4%, respectively. Based on ¹H-NMR spectroscopic study, the oligosaccharides were identified as gluco-oligosaccharides that consisted of 23.63% α-1,4 glycosidic linkages and 76.37% α-1,6 glycosidic linkages with an average molecular weight of 1137 Da. The oligosaccharides promoted the growth of bacterial and yeast strains, including Lactobacillus plantarum, L. paracasei, L. johnsonii, Leuconostoc mesenteroides, L. rhamnosus, and Saccharomyces cerevisiae. When lipopolysaccharide-stimulated RAW 264.7 cells were treated with the oligosaccharides, the production of nitric oxide was decreased; the expression of inducible nitric oxide synthase, tumor necrosis factor-α, interleukin (IL)-1β, IL-6, and IL-10 was suppressed; and the nuclear factor-kappa B signaling pathway was inhibited. In conclusion, the gluco-oligosaccharides obtained from Leu. lactis SBC001 exhibited a prebiotic effect on six bacterial and yeast strains and anti-inflammatory activity in RAW 264.7 macrophage cells.

Identification and Characterization of the Small Heat Shock Protein Hsp20 from Oenococcus oeni SD-2a

Oenococcus oeni can exert its function in hostile wine conditions during the malolactic fermentation process. Therefore, it is an important microbial resource for exploring resistance genes. Hsp20 is an important small heat shock protein from O. oeni. The conserved consensus motif "A-x-x-x-x-G-x-L" of Hsp20 announced its role as a member of the small heat shock protein family. The hsp20 gene from O. oeni SD-2a was cloned to create the recombinant plasmid pTriEx-Hsp20. The recombinant plasmid was transformed into Escherichia coli BL21(DE3) competent cells, and the Hsp20 protein was induced by isopropyl-β-D-thiogalactoside (IPTG). The hsp20 gene from O. oeni SD-2a was successfully expressed, and a 20-kDa fusion protein was identified by SDS-PAGE. The purified Hsp20 protein was obtained using Ni-affinity chromatography. Additionally, BL21(DE3)/Hsp20 and BL21(DE3)/Ctrl were treated at high temperatures of 42 and 52 °C, at pH values of 2.0-12.0, under oxidative shock with 0.1% (v/v) and 0.2% (v/v) H₂O₂, and under an osmotic shock of 430 and 860 mM NaCl to compare the effects of heterologous expression of the Hsp20 protein from O. oeni SD-2a for stress resistance. Notably, Hsp20 overexpression showed enhanced resistance than the control strain did when confronted with different elevated stress conditions. The results demonstrated heterologous expression of the hsp20 gene from O. oeni SD-2a significantly improved the resistance of the host E. coli bacteria against stress conditions.

Virulence of Leuconostoc phages: Influence of stress conditions associated to dairy processes on their host-phage interactions

In this work, we assessed the impact of technological cell stress conditions, commonly present in industrial dairy processes, on the host strain-phage interactions in Leuconostoc. Adsorption and burst size of LDG (Leuconostoc pseudomesenteroides) and Ln-9 (Leuconostoc mesenteroides) phages were evaluated under the following conditions: i) MRS broth, 30 °C; ii) MRS broth at pH 5.5, 30 °C (acidic stress); iii) MRS broth added of NaCl at 4% w/v, 30 °C (osmotic stress) and iv) MRS broth, 10 °C (cold stress). Experiences were performed with the host strains growing both in MRS broth (30 °C) and under stress conditions. On the other hand, the effect of diverse levels of NaCl, KCl, saccharose and glucose on the adsorption for LDG phage was evaluated. Acidic and cold conditions did not significantly affect the adsorption rates for any phage. However, adsorption rate of phage LDG was highly reduced under osmotic stress (NaCl), except when the host strain previously grew in presence of the salt. LDG phage adsorption was not modified by addition of saccharides, but it drastically decreased in presence of salts. Acidic conditions did not affect the burst size for LDG phage, but Ln-9 phage diminished this parameter (61 phage particles/infected cell). Latency time showed a lengthening of 10 min for both phages, while the burst time remained unaltered for LDG and it was delayed 10 min for Ln-9. LDG phage did not propagate under osmotic conditions, but Ln-9 phage released phage particles with an important increase of its latent period and burst time. No phage particles were released within 90 min after the adsorption step under cold stress. This is the first report about this subject. Under certain conditions of technological stress (osmotic and cold) associated to dairy processes, phage infections on the two systems studied in this work could be delayed/inhibited.

Response of Leuconostoc strains against technological stress factors: Growth performance and volatile profiles

The ability of twelve strains belonging to three Leuconostoc species (Leuconostoc mesenteroides, Leuconostoc lactis and Leuconostoc pseudomesenteroides) to grow under diverse sub-lethal technological stress conditions (cold, acidic, alkaline and osmotic) was evaluated in MRS broth. Two strains, Leuconostoc lactis Ln N6 and Leuconostoc mesenteroides Ln MB7, were selected based on their growth under sub-lethal conditions, and volatile profiles in RSM (reconstituted skim milk) at optimal and under stress conditions were analyzed. Growth rates under sub-lethal conditions were strain- and not species-dependent. Volatilomes obtained from the two strains studied were rather diverse. Particularly, Ln N6 (Ln. lactis) produced more ethanol and acetic acid than Ln MB7 (Ln. mesenteroides) and higher amounts and diversity of the rest of volatile compounds as well, at all times of incubation. For the two strains studied, most of stress conditions applied diminished the amounts of ethanol and acetic acid produced and the diversity and levels of the rest of volatile compounds. These results were consequence of the different capacity of the strains to grow under each stress condition tested.

Potential Probiotic Microorganisms in Kefir

Probiotic microorganisms are defined as living microorganisms that provide health benefits on the host when administered in adequate amounts. The benefits include improvement of microbial balance immune system and oral health, provision of cholesterol-lowering effect, and antimicrobial activity against a wide variety of bacteria and some fungi. Kefir microbiota contains active living microorganisms. Many researches were carried out that potential probiotic bacteria such as Lactobacillus acidophilus, Lactobacillus plantarum, Lactobacillus kefir, Lactobacillus kefiranofaciens, Leuconostoc mesenteroides, or yeasts like microorganisms such as Saccharomyces cerevisiae, Kluyveromyces lactis, and Kluyveromyces marxianus were isolated from kefir grains. This chapter presents the data both on the probiotic bacteria isolated from kefir grains or kefir and the probiotic properties of kefir produced with these microorganisms.

Safety of Novel Microbes for Human Consumption: Practical Examples of Assessment in the European Union

Novel microbes are either newly isolated genera and species from natural sources or bacterial strains derived from existing bacteria. Novel microbes are gaining increasing attention for the general aims to preserve and modify foods and to modulate gut microbiota. The use of novel microbes to improve health outcomes is of particular interest because growing evidence points to the importance of gut microbiota in human health. As well, some recently isolated microorganisms have promise for use as probiotics, although in-depth assessment of their safety is necessary. Recent examples of microorganisms calling for more detailed evaluation include Bacteroides xylanisolvens, Akkermansia muciniphila, fructophilic lactic acid bacteria (FLAB), and Faecalibacterium prausnitzii. This paper discusses each candidate's safety evaluation for novel food or novel food ingredient approval according to European Union (EU) regulations. The factors evaluated include their beneficial properties, antibiotic resistance profiling, history of safe use (if available), publication of the genomic sequence, toxicological studies in agreement with novel food regulations, and the qualified presumptions of safety. Sufficient evidences have made possible to support and authorize the use of heat-inactivated B. xylanisolvens in the European Union. In the case of A. muciniphila, the discussion focuses on earlier safety studies and the strain's suitability. FLAB are also subjected to standard safety assessments, which, along with their proximity to lactic acid bacteria generally considered to be safe, may lead to novel food authorization in the future. Further research with F. prausnitzii will increase knowledge about its safety and probiotic properties and may lead to its future use as novel food. Upcoming changes in EUU Regulation 2015/2283 on novel food will facilitate the authorization of future novel products and might increase the presence of novel microbes in the food market.