Maite Muniesa | University of Barcelona (original) (raw)
Papers by Maite Muniesa
Water science and technology : a journal of the International Association on Water Pollution Research, 2003
Verotoxigenic Escherichia coli strains have been related with waterborne outbreaks. Besides 0157:... more Verotoxigenic Escherichia coli strains have been related with waterborne outbreaks. Besides 0157:H7, several serotypes of E. coli and other enterobacteria have been implicated in outbreaks and reported to carry the shiga toxin genes. Shiga toxins, stx1 and stx2, are important virulence factors of these strains. These genes have been linked to bacteriophages and consequently are susceptible to lateral transmission. To better understand the ecology of these genes a study of the presence of the shiga toxin 2 gene (stx2) among coliform bacteria present in sewage samples was carried out. A procedure based on colony hybridisation was developed for the isolation of enterobacteria carrying this gene. Colony growth on Chromocult agar was transferred to a membrane and hybridised with a gene specific probe. The procedure allowed detection of about one colony carrying the gene among around 1,000 faecal coliform colonies. The numbers of bacteria carrying the gene in sewage were also estimated by...
FEMS Microbiology Letters, 2005
MicrobiologyOpen, 2015
Bacteroides spp. have been proposed as indicators of fecal contamination in microbial source trac... more Bacteroides spp. have been proposed as indicators of fecal contamination in microbial source tracking (MST) methodologies. The aim of this study was to develop new qPCR assays that target host-specific Bacteroidal 16S ribosomal RNA genes, to determine the source of fecal contamination in water. Denaturing gradient gel electrophoresis (DGGE) was used to select for host-specific bands of Bacteroides associated with a fecal pollution source and later to design four qPCR host-specific assays. A set of common primers for Bacteroides spp., four different Bacteroides spp. host-associated hydrolysis probes (human, cattle, pig, and poultry), and one hydrolysis probe for the Bacteroides genus were designed. This set of qPCR assays together with other previously developed Bacteroidetes MST targets were used to analyze water samples with fecal contamination from the four sources studied. The host-specific Bacteroides qPCRs designed for human (HMprobeBac), pig (PGprobeBac), and poultry (PLprobeBac) were highly specific for its sources (1.0, 0.97, and 1.0, respectively) although its sensitivity was lower (0.45, 0.50, and 0.73, respectively). The cattle-specific qPCR was totally unspecific and was discarded for future experiments. When compared to previously designed assays, the human and pig qPCRs showed better accuracies (0.86 and 0.84) than their counterparts HF183 and Pig-2-Bac (0.38 and 0.65). Thus, the newly designed human, pig, and poultry qPCR assays outperform other methods developed until date and may be useful for source tracking purposes.
Environmental Microbiology, 2015
Lysogeny by temperate phages provides novel functions for bacteria and shelter for phages. Howeve... more Lysogeny by temperate phages provides novel functions for bacteria and shelter for phages. However, under conditions that activate the phage lytic cycle, the benefit of lysogeny becomes a paradox that poses a threat for bacterial population survival. Using Escherichia coli lysogens for Shiga toxin (Stx) phages as model, we demonstrate how lysogenic bacterial populations circumvent extinction after phage induction. A fraction of cells maintain lysogeny, allowing population survival, while the other fraction of cells lyse, increasing Stx production and spreading Stx phages. The uninduced cells were still lysogenic for the Stx phage and equally able to induce phages as the original cells, suggesting heterogeneity of the E. coli lysogenic population. The bacterial population can modulate phage induction under stress conditions by the stress regulator RpoS. Cells overexpressing RpoS reduce Stx phage induction and compete with and survive better than cells with baseline RpoS levels. Our observations suggest that population heterogeneity in phage induction could be widespread among other bacterial genera and we propose this is a mechanism positively selected to prevent the extinction of the lysogenic population that can be modulated by environmental conditions.
Environmental Microbiology, 2015
Stx bacteriophages are involved in the pathogenicity of Stx-producing Escherichia coli. Induction... more Stx bacteriophages are involved in the pathogenicity of Stx-producing Escherichia coli. Induction of the Stx phage lytic cycle increases Stx expression and releases Stx phages that reach extracellular environments. Stx phage family comprises different phages that harbour any stx subtype. Stx2 is closely related with severe disease and therefore previous studies focused on free Stx2 phages in extraintestinal environments. To provide similar information regarding Stx1 phages, we evaluate free Stx1 phages in 357 samples of human and animal wastewater, faeces, river water, soil, sludge and food. Our method, based on quantification of stx1 in the DNA from the viral fraction, was validated using electron microscopy counting of phages and infectivity. The overall prevalence of Stx1 phages was very low: 7.6% of positive samples and values below 3 × 10(3) GC (gene copies) ml(-1) . These results contrast starkly with the abundance of Stx2 phages in the samples (68.4%). This environmental scarcity of free Stx1 phages is attributed to their lower rates of induction and the fact that Stx1 does not require phage induction to be expressed because it possesses an independent promoter. The implications of the low prevalence of free Stx1 phages for the emergence of new pathogenic strains in the environment are discussed.
Anton Leeuwenhoek Int J Gen M, 2003
Applied and Environmental Microbiology, Dec 1, 1999
Applied and Environmental Microbiology
Shiga toxin-converting bacteriophages are involved in the pathogenicity of some enteric bacteria,... more Shiga toxin-converting bacteriophages are involved in the pathogenicity of some enteric bacteria, such as Escherichia coli O157:H7, but data on the occurrence and distribution of such phages as free particles in nature were not available. An experimental approach has been developed to detect the presence of the Shiga toxin 2 (Stx 2)-encoding bacteriophages in sewage. The Stx 2 gene was amplified by PCR from phages concentrated from 10-ml samples of sewage. Moreover, the phages carrying the Stx 2 gene were detected in supernatants from bacteriophage enrichment cultures by using an Stx 2-negative E. coli O157:H7 strain infected with phages purified from volumes of sewage as small as 0.02 ml. Additionally, the A subunit of Stx 2 was detected in the supernatants of the bacteriophage enrichment cultures, which also showed cytotoxic activity for Vero cells. By enrichment of phages concentrated from different volumes of sewage and applying the most-probable-number technique, it was estimat...
Zoonoses and Public Health
Environmental Microbiology Reports
Stigmatella allrantiaca, a myxomycete-Iooking myxobacterium, found in Collserola Park (Catalonia)... more Stigmatella allrantiaca, a myxomycete-Iooking myxobacterium, found in Collserola Park (Catalonia). Stigmatella aurantiaca has been found on plant debris collected in ColIserola, near Barcelona (Catalonia). It belongs to myxobacteria, a group of procariotes rarely found forming fruiting bodies in the nature, where it may easily be confused with an immature myxomycete. It forms clusters of tiny fruiting bodies, orange coloured, on white stalks. RESUM. Stigmatella allrantiaca, un mixobacteri amb aspecte de mixomicet, trobat al Parc de Collserola (Catalunya). Stigmatella aurantiaca ha estat trobada sobre restes vegetals recol·lectades a Collserola, prop de Barcelona (Catalunya). Es tracta d'un mixobacteri que rarament es pot veure formant cossos fructífers a la natura i es pot confondre fàcilment amb un mixomicet immadur. Forma grups de cossos fructífers molt petits, de color taronja, portats per pedicels blancs.
Bacterial viruses, also known as phages, are the most abundant biological entities on Earth and o... more Bacterial viruses, also known as phages, are the most abundant biological entities on Earth and one of the keys of the control of bacterial populations. In the last decades, the relevance of phages has been increasing because of new insights about the presence of phages in many bacterial genomes, the role of phages in horizontal gene transfer, the phage-bacterium interactions as well as about defense mechanisms of bacteria against phage infection. New biotechnological applications of phages have also been proposed. The most remarkable is the use of phages as antimicrobials. Resistance of bacteria to antibiotics is continually increasing and it severely undermines the ability to control infectious diseases, being currently one of the most challenging problems in public health care. Governments counsel better control of antibiotic usage in both humans and livestock, while researchers look ahead for new generations of antibiotics that can stave off new pathogens. However, a search for ...
Applied and environmental microbiology, 1996
A differential medium (VP8) and a specific probe, based on the variable region V3 of the 16S rRNA... more A differential medium (VP8) and a specific probe, based on the variable region V3 of the 16S rRNA gene, for the detection of Vibrio proteolyticus are defined. The medium contains 8% NaCl, which allows selective growth of moderately halophilic Vibrio strains. D-Sorbitol, as the main carbon source, differentiates the species that can ferment it by the pH indicators cresol red and bromothymol blue. V. proteolyticus and 8 of 418 strains studied grew on the medium and used the D-sorbitol, forming bright yellow colonies. An oligonucleotide, based on the variable region V3 of the 16S rRNA gene (5'CGCTAACGTCAAATAATGCATCTA3'), was used as the specific probe (V3VPR). Only three strains of Vibrio sp. and one strain identified as V. natriegens cross-hybridized with the probe. However, unlike V. proteolyticus, none of the strains grew on VP8. The combined use of VP8 medium and the probe allowed an unequivocal identification of V. proteolyticus.
Applied and environmental microbiology, 1998
Shiga toxin-converting bacteriophages are involved in the pathogenicity of some enteric bacteria,... more Shiga toxin-converting bacteriophages are involved in the pathogenicity of some enteric bacteria, such as Escherichia coli O157:H7, but data on the occurrence and distribution of such phages as free particles in nature were not available. An experimental approach has been developed to detect the presence of the Shiga toxin 2 (Stx 2)-encoding bacteriophages in sewage. The Stx 2 gene was amplified by PCR from phages concentrated from 10-ml samples of sewage. Moreover, the phages carrying the Stx 2 gene were detected in supernatants from bacteriophage enrichment cultures by using an Stx 2-negative E. coli O157:H7 strain infected with phages purified from volumes of sewage as small as 0.02 ml. Additionally, the A subunit of Stx 2 was detected in the supernatants of the bacteriophage enrichment cultures, which also showed cytotoxic activity for Vero cells. By enrichment of phages concentrated from different volumes of sewage and applying the most-probable-number technique, it was estimat...
Applied and environmental microbiology, 1999
The behavior outside the gut of seeded Escherichia coli O157:H7, naturally occurring E. coli, som... more The behavior outside the gut of seeded Escherichia coli O157:H7, naturally occurring E. coli, somatic coliphages, bacteriophages infecting O157:H7, and Shiga toxin 2 (Stx2)-encoding bacteriophages was studied to determine whether the last persist in the environment more successfully than their host bacteria. The ratios between the numbers of E. coli and those of the different bacteriophages were clearly lower in river water than in sewage of the area, whereas the ratios between the numbers of the different phages were similar. In addition, the numbers of bacteria decreased between 2 and 3 log units in in situ survival experiments performed in river water, whereas the numbers of phages decreased between 1 and 2 log units. Chlorination and pasteurization treatments that reduced by approximately 4 log units the numbers of bacteria reduced by less than 1 log unit the numbers of bacteriophages. Thus, it can be concluded that Stx2-encoding phages persist longer than their host bacteria in...
Water science and technology : a journal of the International Association on Water Pollution Research, 2003
Verotoxigenic Escherichia coli strains have been related with waterborne outbreaks. Besides 0157:... more Verotoxigenic Escherichia coli strains have been related with waterborne outbreaks. Besides 0157:H7, several serotypes of E. coli and other enterobacteria have been implicated in outbreaks and reported to carry the shiga toxin genes. Shiga toxins, stx1 and stx2, are important virulence factors of these strains. These genes have been linked to bacteriophages and consequently are susceptible to lateral transmission. To better understand the ecology of these genes a study of the presence of the shiga toxin 2 gene (stx2) among coliform bacteria present in sewage samples was carried out. A procedure based on colony hybridisation was developed for the isolation of enterobacteria carrying this gene. Colony growth on Chromocult agar was transferred to a membrane and hybridised with a gene specific probe. The procedure allowed detection of about one colony carrying the gene among around 1,000 faecal coliform colonies. The numbers of bacteria carrying the gene in sewage were also estimated by...
FEMS Microbiology Letters, 2005
MicrobiologyOpen, 2015
Bacteroides spp. have been proposed as indicators of fecal contamination in microbial source trac... more Bacteroides spp. have been proposed as indicators of fecal contamination in microbial source tracking (MST) methodologies. The aim of this study was to develop new qPCR assays that target host-specific Bacteroidal 16S ribosomal RNA genes, to determine the source of fecal contamination in water. Denaturing gradient gel electrophoresis (DGGE) was used to select for host-specific bands of Bacteroides associated with a fecal pollution source and later to design four qPCR host-specific assays. A set of common primers for Bacteroides spp., four different Bacteroides spp. host-associated hydrolysis probes (human, cattle, pig, and poultry), and one hydrolysis probe for the Bacteroides genus were designed. This set of qPCR assays together with other previously developed Bacteroidetes MST targets were used to analyze water samples with fecal contamination from the four sources studied. The host-specific Bacteroides qPCRs designed for human (HMprobeBac), pig (PGprobeBac), and poultry (PLprobeBac) were highly specific for its sources (1.0, 0.97, and 1.0, respectively) although its sensitivity was lower (0.45, 0.50, and 0.73, respectively). The cattle-specific qPCR was totally unspecific and was discarded for future experiments. When compared to previously designed assays, the human and pig qPCRs showed better accuracies (0.86 and 0.84) than their counterparts HF183 and Pig-2-Bac (0.38 and 0.65). Thus, the newly designed human, pig, and poultry qPCR assays outperform other methods developed until date and may be useful for source tracking purposes.
Environmental Microbiology, 2015
Lysogeny by temperate phages provides novel functions for bacteria and shelter for phages. Howeve... more Lysogeny by temperate phages provides novel functions for bacteria and shelter for phages. However, under conditions that activate the phage lytic cycle, the benefit of lysogeny becomes a paradox that poses a threat for bacterial population survival. Using Escherichia coli lysogens for Shiga toxin (Stx) phages as model, we demonstrate how lysogenic bacterial populations circumvent extinction after phage induction. A fraction of cells maintain lysogeny, allowing population survival, while the other fraction of cells lyse, increasing Stx production and spreading Stx phages. The uninduced cells were still lysogenic for the Stx phage and equally able to induce phages as the original cells, suggesting heterogeneity of the E. coli lysogenic population. The bacterial population can modulate phage induction under stress conditions by the stress regulator RpoS. Cells overexpressing RpoS reduce Stx phage induction and compete with and survive better than cells with baseline RpoS levels. Our observations suggest that population heterogeneity in phage induction could be widespread among other bacterial genera and we propose this is a mechanism positively selected to prevent the extinction of the lysogenic population that can be modulated by environmental conditions.
Environmental Microbiology, 2015
Stx bacteriophages are involved in the pathogenicity of Stx-producing Escherichia coli. Induction... more Stx bacteriophages are involved in the pathogenicity of Stx-producing Escherichia coli. Induction of the Stx phage lytic cycle increases Stx expression and releases Stx phages that reach extracellular environments. Stx phage family comprises different phages that harbour any stx subtype. Stx2 is closely related with severe disease and therefore previous studies focused on free Stx2 phages in extraintestinal environments. To provide similar information regarding Stx1 phages, we evaluate free Stx1 phages in 357 samples of human and animal wastewater, faeces, river water, soil, sludge and food. Our method, based on quantification of stx1 in the DNA from the viral fraction, was validated using electron microscopy counting of phages and infectivity. The overall prevalence of Stx1 phages was very low: 7.6% of positive samples and values below 3 × 10(3) GC (gene copies) ml(-1) . These results contrast starkly with the abundance of Stx2 phages in the samples (68.4%). This environmental scarcity of free Stx1 phages is attributed to their lower rates of induction and the fact that Stx1 does not require phage induction to be expressed because it possesses an independent promoter. The implications of the low prevalence of free Stx1 phages for the emergence of new pathogenic strains in the environment are discussed.
Anton Leeuwenhoek Int J Gen M, 2003
Applied and Environmental Microbiology, Dec 1, 1999
Applied and Environmental Microbiology
Shiga toxin-converting bacteriophages are involved in the pathogenicity of some enteric bacteria,... more Shiga toxin-converting bacteriophages are involved in the pathogenicity of some enteric bacteria, such as Escherichia coli O157:H7, but data on the occurrence and distribution of such phages as free particles in nature were not available. An experimental approach has been developed to detect the presence of the Shiga toxin 2 (Stx 2)-encoding bacteriophages in sewage. The Stx 2 gene was amplified by PCR from phages concentrated from 10-ml samples of sewage. Moreover, the phages carrying the Stx 2 gene were detected in supernatants from bacteriophage enrichment cultures by using an Stx 2-negative E. coli O157:H7 strain infected with phages purified from volumes of sewage as small as 0.02 ml. Additionally, the A subunit of Stx 2 was detected in the supernatants of the bacteriophage enrichment cultures, which also showed cytotoxic activity for Vero cells. By enrichment of phages concentrated from different volumes of sewage and applying the most-probable-number technique, it was estimat...
Zoonoses and Public Health
Environmental Microbiology Reports
Stigmatella allrantiaca, a myxomycete-Iooking myxobacterium, found in Collserola Park (Catalonia)... more Stigmatella allrantiaca, a myxomycete-Iooking myxobacterium, found in Collserola Park (Catalonia). Stigmatella aurantiaca has been found on plant debris collected in ColIserola, near Barcelona (Catalonia). It belongs to myxobacteria, a group of procariotes rarely found forming fruiting bodies in the nature, where it may easily be confused with an immature myxomycete. It forms clusters of tiny fruiting bodies, orange coloured, on white stalks. RESUM. Stigmatella allrantiaca, un mixobacteri amb aspecte de mixomicet, trobat al Parc de Collserola (Catalunya). Stigmatella aurantiaca ha estat trobada sobre restes vegetals recol·lectades a Collserola, prop de Barcelona (Catalunya). Es tracta d'un mixobacteri que rarament es pot veure formant cossos fructífers a la natura i es pot confondre fàcilment amb un mixomicet immadur. Forma grups de cossos fructífers molt petits, de color taronja, portats per pedicels blancs.
Bacterial viruses, also known as phages, are the most abundant biological entities on Earth and o... more Bacterial viruses, also known as phages, are the most abundant biological entities on Earth and one of the keys of the control of bacterial populations. In the last decades, the relevance of phages has been increasing because of new insights about the presence of phages in many bacterial genomes, the role of phages in horizontal gene transfer, the phage-bacterium interactions as well as about defense mechanisms of bacteria against phage infection. New biotechnological applications of phages have also been proposed. The most remarkable is the use of phages as antimicrobials. Resistance of bacteria to antibiotics is continually increasing and it severely undermines the ability to control infectious diseases, being currently one of the most challenging problems in public health care. Governments counsel better control of antibiotic usage in both humans and livestock, while researchers look ahead for new generations of antibiotics that can stave off new pathogens. However, a search for ...
Applied and environmental microbiology, 1996
A differential medium (VP8) and a specific probe, based on the variable region V3 of the 16S rRNA... more A differential medium (VP8) and a specific probe, based on the variable region V3 of the 16S rRNA gene, for the detection of Vibrio proteolyticus are defined. The medium contains 8% NaCl, which allows selective growth of moderately halophilic Vibrio strains. D-Sorbitol, as the main carbon source, differentiates the species that can ferment it by the pH indicators cresol red and bromothymol blue. V. proteolyticus and 8 of 418 strains studied grew on the medium and used the D-sorbitol, forming bright yellow colonies. An oligonucleotide, based on the variable region V3 of the 16S rRNA gene (5'CGCTAACGTCAAATAATGCATCTA3'), was used as the specific probe (V3VPR). Only three strains of Vibrio sp. and one strain identified as V. natriegens cross-hybridized with the probe. However, unlike V. proteolyticus, none of the strains grew on VP8. The combined use of VP8 medium and the probe allowed an unequivocal identification of V. proteolyticus.
Applied and environmental microbiology, 1998
Shiga toxin-converting bacteriophages are involved in the pathogenicity of some enteric bacteria,... more Shiga toxin-converting bacteriophages are involved in the pathogenicity of some enteric bacteria, such as Escherichia coli O157:H7, but data on the occurrence and distribution of such phages as free particles in nature were not available. An experimental approach has been developed to detect the presence of the Shiga toxin 2 (Stx 2)-encoding bacteriophages in sewage. The Stx 2 gene was amplified by PCR from phages concentrated from 10-ml samples of sewage. Moreover, the phages carrying the Stx 2 gene were detected in supernatants from bacteriophage enrichment cultures by using an Stx 2-negative E. coli O157:H7 strain infected with phages purified from volumes of sewage as small as 0.02 ml. Additionally, the A subunit of Stx 2 was detected in the supernatants of the bacteriophage enrichment cultures, which also showed cytotoxic activity for Vero cells. By enrichment of phages concentrated from different volumes of sewage and applying the most-probable-number technique, it was estimat...
Applied and environmental microbiology, 1999
The behavior outside the gut of seeded Escherichia coli O157:H7, naturally occurring E. coli, som... more The behavior outside the gut of seeded Escherichia coli O157:H7, naturally occurring E. coli, somatic coliphages, bacteriophages infecting O157:H7, and Shiga toxin 2 (Stx2)-encoding bacteriophages was studied to determine whether the last persist in the environment more successfully than their host bacteria. The ratios between the numbers of E. coli and those of the different bacteriophages were clearly lower in river water than in sewage of the area, whereas the ratios between the numbers of the different phages were similar. In addition, the numbers of bacteria decreased between 2 and 3 log units in in situ survival experiments performed in river water, whereas the numbers of phages decreased between 1 and 2 log units. Chlorination and pasteurization treatments that reduced by approximately 4 log units the numbers of bacteria reduced by less than 1 log unit the numbers of bacteriophages. Thus, it can be concluded that Stx2-encoding phages persist longer than their host bacteria in...