RESUMEN
Bacterial pathogens, such as Shiga toxin-producing Escherichia coli (STEC) and Shigella spp., are important causes of foodborne illness internationally. Recovery of these organisms from foods is critical for food safety investigations to support attribution of illnesses to specific food commodities; however, isolation of bacterial cultures can be challenging. Methods for the isolation of STEC and Shigella spp. from foods typically require enrichment to amplify target organisms to detectable levels. Yet, during enrichment, target organisms can be outcompeted by other bacteria in food matrices due to faster growth rates, or through production of antimicrobial agents such as bacteriocins or bacteriophages. The purpose of this study was to evaluate the occurrence of Shigella and STEC inhibitors produced by food microbiota. The production of antimicrobial compounds in cell-free extracts from 200 bacterial strains and 332 food-enrichment broths was assessed. Cell-free extracts produced by 23 (11.5%) of the strains tested inhibited growth of at least one of the five Shigella and seven STEC indicator strains used in this study. Of the 332 enrichment broths tested, cell-free extracts from 25 (7.5%) samples inhibited growth of at least one of the indicator strains tested. Inhibition was most commonly associated with E. coli recovered from meat products. Most of the inhibiting compounds were determined to be proteinaceous (34 of the 48 positive samples, 71%; including 17 strains, 17 foods) based on inactivation by proteolytic enzymes, indicating presence of bacteriocins. The cell-free extracts from 13 samples (27%, eight strains, five foods) were determined to contain bacteriophages based on the observation of plaques in diluted extracts and/or resistance to proteolytic enzymes. These results indicate that the production of inhibitors by food microbiota may be an important challenge for the recovery of foodborne pathogens, particularly for Shigella sonnei. The performance of enrichment media for recovery of Shigella and STEC could be improved by mitigating the impact of inhibitors produced by food microbiota during the enrichment process.
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Listeria monocytogenes, a Gram-positive, rod-shaped, non-spore-forming bacterium, is an important foodborne bacterial pathogen for humans worldwide. Here, we report the complete genome sequence of a Canadian Listeria monocytogenes strain with an antimicrobial resistance (AMR) gene that was isolated from lettuce.
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Listeria monocytogenes, a Gram-positive, rod-shaped, non-spore-forming bacterium, is an important foodborne bacterial pathogen for humans worldwide, with a high mortality rate. Here, we report the complete genome sequence of a Listeria monocytogenes strain with an antimicrobial resistance (AMR) gene, isolated from sprouts in Canada.
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Listeria monocytogenes is a Gram-positive, rod-shaped, non-spore-forming bacterium which is an important foodborne bacterial pathogen for human worldwide with 20-30% mortality. Here, we report circular complete genome sequences of three Listeria monocytogenes strains isolated from the samples of microgreens in Canada.
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Listeria monocytogenes is a Gram-positive, rod-shaped, non-spore-forming bacterium that is an important foodborne bacterial pathogen for humans worldwide, with high mortality rates. Here, we report the complete genome sequence of a Listeria monocytogenes strain that was isolated from kale salad in Canada.
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Using a combination of Illumina paired-end sequencing, Pacific Biosciences RS II sequencing, and OpGen Argus whole-genome optical mapping, we report here the first complete genome sequence of Yersinia massiliensis The completed genome consists of a 4.99-Mb chromosome, a 121-kb megaplasmid, and a 57-kb plasmid.
RESUMEN
The determination of Shiga toxin (ST) subtypes can be an important element in the risk characterization of foodborne ST-producing Escherichia coli (STEC) isolates for making risk management decisions. ST subtyping methods include PCR techniques based on electrophoretic or pyrosequencing analysis of amplicons and in silico techniques based on whole genome sequence analysis using algorithms that can be readily incorporated into bioinformatics analysis pipelines for characterization of isolates by their genetic composition. The choice of technique will depend on the performance characteristics of the method and an individual laboratory's access to specialized equipment or personnel. We developed two whole genome sequence-based ST subtyping tools: (i) an in silico PCR algorithm requiring genome assembly to replicate a reference PCR-based method developed by the Statens Serum Institut (SSI) and (ii) an assembly-independent routine in which raw sequencing results are mapped to a database of known ST subtype sequence variants (V-Typer). These tools were evaluated alongside the SSI reference PCR method and a recently described PCR-based pyrosequencing technique. The V-Typer method results corresponded closely with the reference method in the analysis of 67 STEC cultures obtained from a World Health Organization National Reference Laboratory. In contrast, the in silico PCR method failed to detect ST subtypes in several cases, a result which we attribute to assembly-induced errors typically encountered with repetitive gene sequences. The V-Typer can be readily integrated into bioinformatics protocols used in the identification and characterization of foodborne STEC isolates.
Asunto(s)
Infecciones por Escherichia coli/diagnóstico , Toxina Shiga/genética , Proteínas de Escherichia coli/genética , Genómica , Humanos , Toxina Shiga I/genética , Toxina Shiga II/genética , Escherichia coli Shiga-Toxigénica/aislamiento & purificaciónRESUMEN
Shiga toxin (stx)-producing Escherichia coli (STEC) contamination in food and water is one of the most recognized concerns and a major financial burden in human hygiene control worldwide. Rapid and highly reliable methods of detecting and identifying STEC causing gastroenteric illnesses are crucial to prevent foodborne outbreaks. A number of tests have been developed and commercialized to detect STEC using molecular microbiology techniques. Most of these are designed to identify virulence factors such as Shiga toxin and intimin as well as E. coli O and H antigen serotype specific genes. In order to screen pathogenic STEC without relying on O:H serotyping, we developed a rapid detection and genotyping assay for STEC virulence genes using a PCR-pyrosequencing application. We adapted the PyroMark Q24 Pyrosequencing platform for subtyping 4 major virulence genes, Shiga toxin 1 and 2 (stx1 and stx2), intimin (eae) and O157-antigen gene cluster target rfbE, using Single Nucleotide Polymorphism (SNP) analysis. A total of 224 E. coli strains including isolates from Canadian environment, food and clinical cases were examined. Based on the multiple alignment analysis of 30-80 base nucleotide pyrogram reads, three alleles of the Shiga toxin 1a gene (stx1a) (stx1a-I, stx1a-II, stx1a-III) were identified. Results of the stx1, stx2, eae and rfbE genotyping revealed that each group of O:H serotype shares distinctive characteristics that could be associated with the virulence of each genotype. O157:H7/NM carries stx1a-II (94%), stx2a (82%), λ/γ1-eae (100%) and rfbE type-H7/NM (100%). Whereas isolates of the "Top-6" serotypes (O26, O45, O103, O111, O121, O145) had a high incidence of stx1a-I (90%) and stx2a (100%). stx1a-III (60%) was only observed in non Top-7 (Top-6 plus O157) STEC and Shigella spp. The entire assay, from extracting DNA from colonies on a plate to the generation of sequence information, can be completed in 5h. The method of profiling these 4 STEC pathogenic genotypes as demonstrated in this paper is rapid, easily performed, informative and cost-effective, and thus has a potential to be deployed in the food industry for the routine screening of potentially pathogenic STEC isolates.
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Adhesinas Bacterianas/genética , Técnicas Bacteriológicas/métodos , Carbohidrato Epimerasas/genética , Proteínas de Escherichia coli/genética , Escherichia coli/clasificación , Escherichia coli/genética , Técnicas de Genotipaje/métodos , Toxina Shiga/genética , Transaminasas/genética , Canadá , Infecciones por Escherichia coli/microbiología , Infecciones por Escherichia coli/prevención & control , Microbiología de Alimentos , Enfermedades Transmitidas por los Alimentos/microbiología , Enfermedades Transmitidas por los Alimentos/prevención & control , Genotipo , Humanos , Tipificación Molecular/métodos , Análisis de Secuencia de ADN/métodos , Factores de TiempoRESUMEN
ELL-associated protein 30 (EAP30) was initially characterized as a component of the Holo-ELL complex, which contains the elongation factor ELL. Both ELL and Holo-ELL stimulate RNA pol II elongation in vitro. However, ELL and not Holo-ELL inhibits RNA pol II initiation. It is not clear how these two discrete functions of ELL are regulated. Here we report that mini-chromosome maintenance 2 (MCM2) binds to EAP30 and show that MCM2 competes with ELL for binding to EAP30 thus potentially modulating the stability of Holo-ELL.
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Proteínas Nucleares/metabolismo , Factores de Transcripción/metabolismo , Animales , Unión Competitiva , Línea Celular , Células HeLa , Humanos , Proteínas Nucleares/química , Proteínas Nucleares/genética , Unión Proteica , Factores de Transcripción/genética , Técnicas del Sistema de Dos HíbridosRESUMEN
The establishment of silent chromatin requires passage through S-phase, but not DNA replication per se. Nevertheless, many proteins that affect silencing are bona fide DNA replication factors. It is not clear if mutations in these replication factors affect silencing directly or indirectly via deregulation of S-phase or DNA replication. Consequently, the relationship between DNA replication and silencing remains an issue of debate. Here we analyze the effect of mutations in DNA replication factors (mcm5-461, mcm5-1, orc2-1, orc5-1, cdc45-1, cdc6-1, and cdc7-1) on the silencing of a group of reporter constructs, which contain different combinations of "natural" subtelomeric elements. We show that the mcm5-461, mcm5-1, and orc2-1 mutations affect silencing through subtelomeric ARS consensus sequences (ACS), while cdc6-1 affects silencing independently of ACS. orc5-1, cdc45-1, and cdc7-1 affect silencing through ACS, but also show ACS-independent effects. We also demonstrate that isolated nontelomeric ACS do not recapitulate the same effects when inserted in the telomere. We propose a model that defines the modes of action of MCM5 and CDC6 in silencing.