Phenotypic, Technological, Safety, and Genomic Profiles of Gamma-Aminobutyric Acid-Producing Lactococcus lactis and Streptococcus thermophilus Strains Isolated from Cow's Milk.

Gamma-aminobutyric acid (GABA)-producing lactic acid bacteria (LAB) can be used as starters in the development of GABA-enriched functional fermented foods. In this work, four GABA-producing strains each of Lactococcus lactis and Streptococcus thermophilus species were isolated from cow's milk, and their phenotypic, technological, and safety profiles determined. Genome analysis provided genetic support for the majority of the analyzed traits, namely, GABA production, growth in milk, and the absence of genes of concern. The operon harboring the glutamate decarboxylase gene (gadB) was chromosomally encoded in all strains and showed the same gene content and gene order as those reported, respectively, for L. lactis and S. thermophilus. In the latter species, the operon was flanked (as in most strains of this species) by complete or truncated copies of insertion sequences (IS), suggesting recent acquisition through horizontal gene transfer. The genomes of three L. lactis and two S. thermophilus strains showed a gene encoding a caseinolytic proteinase (PrtP in L. lactis and PrtS in S. thermophilus). Of these, all but one grew in milk, forming a coagulum of good appearance and an appealing acidic flavor and taste. They also produced GABA in milk supplemented with monosodium glutamate. Two L. lactis strains were identified as belonging to the biovar. diacetylactis, utilized citrate from milk, and produced significant amounts of acetoin. None of the strains showed any noticeable antibiotic resistance, nor did their genomes harbor transferable antibiotic resistance genes or genes involved in toxicity, virulence, or pathogenicity. Altogether these results suggest that all eight strains may be considered candidates for use as starters or components of mixed LAB cultures for the manufacture of GABA-enriched fermented dairy products.

Biodiversity of wild Lactococcus lactis and their geo-spatial relationship with the environment.

Lactic acid bacteria are distributed in nature, isolating themselves from diverse ecosystems and presenting a wide metabolic biodiversity. In Corrientes (Argentina), artisanal cheeses and their specific environment are an important source of autochthonous lactic acid bacteria. The objective of this work was to establish associations between the phenotypic characteristics of strains of Lactococcus lactis subsp. lactis native from Corrientes with climatological data of the Province and the characteristics of the soil and the landscapes. Physiological and biochemical characterization data of Lactococcus lactis subsp. lactis isolated from the dairy environment and from different localities of Corrientes will be used. The strains were space-located through Google Earth, flood and drought events were evaluated using Standardized Precipitation Evapotranspiration Index, and soil composition data (A and Bt horizons) in the study areas were obtained from the experimental station National Institute of Agricultural Technology - Corrientes. A statistical analysis was applied to these results (Infostat Software, Di Rienzo et al. 2008). The resulting consists in three conglomerates, differentiating strains from soils coming from "flooded landscapes" and those from "sandy hills landscape". The analysis by main components highlighted the preference of strains from flooded landscapes by a saline-alkaline environment, affecting during periods of drought, and strains from sandy hills landscape by a low medium in salts and acid soil, directly during period of high humidity resulting from previous floods.

Diagnóstico molecular de Porphyromonas gingivalis: optimización del método / Molecular diagnosis of Porphyromonas gingivalis: optimization of the method

El objetivo del presente trabajo fue estandarizar y optimizar la técnica de PCR convencional para detección de Porphyromonas gingivalis ATCC 33277. Materiales y métodos: la cepa de P. gingivalis ATCC332227 se sembró en agar Bruella enriquecido con sangre de cordero, suplementado con hemina y vitamina K. El ADN se extrajo empleando el protocolo que usa bromuro de cetil trimetilamonio (CTAB). Se evaluó la cantidad y calidad del material genético obtenido con el fotómetro UV Ampli-Quat, AQ-07 Nucleic Acid. Se realizó la PCR convencional con diferentes concentraciones de MgCl2 1 mM, 1,5 mM y 2.0 mM y a dos temperaturas de alineamiento: 60ºC y 55ºC. Los productos PCR se separaron por electroforesis en un gel de agarosa 1 por ciento. Las bandas se visualizaron en un fotodocumentador. La sensibilidad se calculó teniendo en cuenta el número de bacterias en diferentes diluciones. Resultados: se obtuvo una concentración 1,55x10(6) ng/ul de ADN genómico a partir de una suspensión bacteriana de 10a células bacterianas/ml, con índice de pureza 1,648 (relación de OD260/OD280). Los mejores resultados se obtuvieron con una concentración de 2 mM de MgCl2 y una temperatura de alineación de 55ºC. En cuanto a la sensibilidad, se obtuvo un límite de detección de 5 x 10/5 uL células bacterianas en suspensión. Conclusión: en la prueba de PCR convencional para Prophyromonas gingivalis ATCC 33277, las condiciones óptimas de estandarización son la concentración de 2 mM de MgCl y 55ºC y es necesaria una carga bacteriana mínima de 5 x 10 células/5 ul como límite de detección.

Metabolitos de bacterias lácticas antagónicos al crecimiento de microorganismos cariogénicos / Antagonistic activity of lactic acid bacteria metabolites toward cariogenic microorganisms growth

Aislar, purificar y conservar cepas de Streptococcus spp. y lactobacillus spp. de la cavidad bucal y enfrentarlas "in vitro" a bacterias lácticas. Materiales y métodos: se seleccionaron individuos con caries y se recolectaron muestras de saliva. Para recuperar Streptococcus spp. se empleó el medio Mitis Salivarius (Difco, Detroit, MI, Estados Unidos) y para Lactobacillus spp. se usó Rogosa (Blokar Diagnostics, Beauvais, Francia). Como cepas productoras de bacteriocinas se utilizaron 7 cepas de Lactococcus lactis subsp. lactis, 2 de Leuconostoc mesenteroides y 1 de Lactococcus lactis subsp. diacetylactis. La actividad antagónica de las bacterias lácticas al crecimiento in vitro de bacterias cariogénicas se determinó con el método de difusión en agar. Resultado: el desarrollo y la multiplicación de las cepas de Streptococcus spp. de origen bucal ensayadas se vieron afectados por la presencia de metabolitos generados por las cepas de Lactococcus lactis subsp. lactis. Conclusión: el crecimiento de las cepas de Streptococcus subsp. fue inhibido por efecto de L. lactis subsp. lactis...

Metabolitos de bacterias lácticas antagónicos al crecimiento de microorganismos cariogénicos / Antagonistic activity of lactic acid bacteria metabolites toward cariogenic microorganisms growth

Aislar, purificar y conservar cepas de Streptococcus spp. y lactobacillus spp. de la cavidad bucal y enfrentarlas "in vitro" a bacterias lácticas. Materiales y métodos: se seleccionaron individuos con caries y se recolectaron muestras de saliva. Para recuperar Streptococcus spp. se empleó el medio Mitis Salivarius (Difco, Detroit, MI, Estados Unidos) y para Lactobacillus spp. se usó Rogosa (Blokar Diagnostics, Beauvais, Francia). Como cepas productoras de bacteriocinas se utilizaron 7 cepas de Lactococcus lactis subsp. lactis, 2 de Leuconostoc mesenteroides y 1 de Lactococcus lactis subsp. diacetylactis. La actividad antagónica de las bacterias lácticas al crecimiento in vitro de bacterias cariogénicas se determinó con el método de difusión en agar. Resultado: el desarrollo y la multiplicación de las cepas de Streptococcus spp. de origen bucal ensayadas se vieron afectados por la presencia de metabolitos generados por las cepas de Lactococcus lactis subsp. lactis. Conclusión: el crecimiento de las cepas de Streptococcus subsp. fue inhibido por efecto de L. lactis subsp. lactis...(AU)

Lactobacillus plantarum bacteriophages isolated from Kefir grains: phenotypic and molecular characterization.

Two greatly related Lactobacillus plantarum bacteriophages (named FAGK1 and FAGK2) were isolated from Kefir grains of different origins. Both phages belonged to the Siphoviridae family (morphotype B1) and showed similar dimensions for head and tail sizes. The host range of the two phages, using 36 strains as potential host strains, differed only in the phage reactivity against one of them. The phages showed latent periods of 30 min, burst periods of 80+/-10 min and burst size values of 11.0+/-1.0 PFU per infected cell as mean value. Identical DNA restriction patterns were obtained for both phages with PvuI, SalI, HindIII and MluI. The viral DNA apparently did not present extremes cos and the structural protein patterns presented four major bands (32.9, 35.7, 43.0 and 66.2 kDa). This study reports the first isolation of bacteriophages of Lb. plantarum from Kefir grains and adds further knowledge regarding the complex microbial community of this fermented milk.