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M Wiedmann

Publications and source records attributed to M Wiedmann.

At least 37 records · Page 2Linked to original sources
PubMed2004

Molecular Subtyping and Tracking of Listeria monocytogenes in Latin-Style Fresh-Cheese Processing Plants.

Latin-style fresh cheeses, which have been linked to at least 2 human listeriosis outbreaks in the United States, are considered to be high-risk foods for Listeria monocytogenes contamination. We evaluated L. monocytogenes contamination patterns in 3 Latin-style fresh-cheese processing plants to gain a better understanding of L. monocytogenes contamination sources in the manufacture of these cheeses. Over a 6-mo period, 246 environmental samples were collected and analyzed for L. monocytogenes using both the Food and Drug Administration (FDA) method and the Biosynth L. monocytogenes detection system (LMDS). Finished cheese samples from the same plants (n = 111) were also analyzed by the FDA method, which was modified to include L. monocytogenes plating medium (LMPM) and the L. monocytogenes confirmatory plating medium (LMCM) used in the LMDS method. Listeria monocytogenes was detected in 6.3% of cheese and 11.0% of environmental samples. Crates, drains, and floor samples showed the highest contamination rates, with 55.6, 30.0, and 20.6% L. monocytogenes positive samples, respectively. Finished products and food contact surfaces were positive in only one plant. The FDA method showed a higher sensitivity than the LMDS method for detection of L. monocytogenes from environmental samples. The addition of LMPM and LMCM media did not further enhance the performance of the FDA method for L. monocytogenes detection from finished products. Molecular subtyping (PCR-based allelic analysis of the virulence genes actA and hly and automated ribotyping) was used to track contamination patterns. Ribotype DUP-1044A, which had previously been linked to a 1998 multistate human listeriosis outbreak in the United States, was the most commonly identified subtype (20/36 isolates) and was isolated from 2 plants. This ribotype was persistent and widespread in one factory, where it was also responsible for the contamination of finished products. We hypothesize that this ribotype may represent a clonal group with a specific ability to persist in food processing environments. While previous listeriosis outbreaks were linked to Latin-style fresh cheeses made from unpasteurized milk, the presence of this organism in pasteurized cheese products illustrates that persistent environmental contamination also represents an important source of finished product contamination.

Cheese↗
PubMed2003

Pathogen, host and environmental factors contributing to the pathogenesis of listeriosis.

Listeriosis is a severe human and animal disease caused by two species of pathogenic bacteria from the genus Listeria, L. monocytogenes and L. ivanovii. In humans, listeriosis is overwhelmingly a foodborne disease, yet much remains to be learned regarding the transmission dynamics of pathogenic Listeria from the environment, through food, to humans. Similarly, our understanding of the various host, pathogen and environmental factors that impact the pathogenesis of listeriosis at the cellular and molecular level is incomplete. This review will summarize what is currently known about animal and human listeriosis, detail the pathogen, host and environmental factors that contribute to pathogenesis and, finally, examine the interactions among those factors that influence the occurrence of human infection.

Animals↗
PubMed2003

ADSA Foundation Scholar Award--An integrated science-based approach to dairy food safety: Listeria monocytogenes as a model system.

Transmission of food- and milkborne pathogens often involves complex interactions among the pathogen, the environment, and one or multiple host species. A complete understanding of these interactions is critical to allow the development of science-based, effective intervention strategies for foodborne infectious diseases. This article summarizes our studies on the transmission, ecology, pathogenesis and population genetics of Listeria monocytogenes, which we have used as model for a food- and milkborne pathogen that infects multiple hosts and also has considerable ability to survive and multiply in nonhost environments. Application of molecular subtyping tools in conjunction with phenotypic characterization of selected strains has allowed us to define distinct L. monocytogenes subtypes and clonal groups that appear to differ in relevant phenotypic characteristics that may affect their abilities to be transmitted through food systems. For example, a genetic group designated as lineage I has been shown to be not only more common among human listeriosis cases than among animal cases, but lineage I strains also appear to show an increased in vitro ability to spread intracellularly from host cell to host cell. These findings are consistent with the fact that while genetically diverse strains may be classified to one bacterial species, these strains often differ from one another in important genetic and phenotypic characteristics. I thus propose that evolutionary- and molecular subtyping-based definitions of bacterial subtypes and clonal groups will provide critical insight into the microbial ecology of dairy food systems, including not only foodborne pathogens, but also organisms important for dairy fermentation and spoilage.

Agriculture↗
PubMed2002

[Recurrent lower gastro-intestinal bleeding in a 38-year-old patient].

HISTORY AND CLINICAL FINDINGS: A 38-year-old patient with a history of recurrent gastrointestinal bleeding for more than 15 years was transferred for the treatment of a new onset of hematochezia and anemia. His general condition was clearly reduced. EXAMINATIONS: Laboratory results showed a distinct microcytic hypochromic anemia; ferrum, ferritin, albumin, and protein were also diminished. Colonoscopy and transrectal ultrasound uncovered large hemangiomatous structures in the rectum. Digital substraction angiography of the bilateral internal iliac artery, superior and inferior mesenteric arteries including its branches showed a perirectal polypoid tumour with a discrete angiomatous structural shadow in the capillary phase. MRI of the pelvis revealed angiomatous blood vessels in the whole pararectal space and to a minor extension in the gluteal muscles. DIAGNOSIS, TREATMENT AND COURSE: The diagnosis of cavernous hemangioma of the rectum was made and a distal mesorectal resection of the rectum including a coloanal anastomosis and double-running ileostomy was performed. 3 months later the ileostomy was reversed. There was no further bleeding and the rectal continence was normal. CONCLUSION: In case of unclear recurrent lower gastrointestinal bleeding, with onset in the early childhood and impressive rectal varices, one has to think about the rare diagnosis of cavernous hemangioma.

Adult↗
PubMed2002

Microtiter plate assay for assessment of Listeria monocytogenes biofilm formation.

Listeria monocytogenes has the ability to form biofilms on food-processing surfaces, potentially leading to food product contamination. The objective of this research was to standardize a polyvinyl chloride (PVC) microtiter plate assay to compare the ability of L. monocytogenes strains to form biofilms. A total of 31 coded L. monocytogenes strains were grown in defined medium (modified Welshimer's broth) at 32 degrees C for 20 and 40 h in PVC microtiter plate wells. Biofilm formation was indirectly assessed by staining with 1% crystal violet and measuring crystal violet absorbance, using destaining solution. Cellular growth rates and final cell densities did not correlate with biofilm formation, indicating that differences in biofilm formation under the same environmental conditions were not due to growth rate differences. The mean biofilm production of lineage I strains was significantly greater than that observed for lineage II and lineage III strains. The results from the standardized microtiter plate biofilm assay were also compared to biofilm formation on PVC and stainless steel as assayed by quantitative epifluorescence microscopy. Results showed similar trends for the microscopic and microtiter plate assays, indicating that the PVC microtiter plate assay can be used as a rapid, simple method to screen for differences in biofilm production between strains or growth conditions prior to performing labor-intensive microscopic analyses.

Bacterial Adhesion↗
PubMed2001

Recurrent Listeria monocytogenes infection: relapse or reinfection with a unique strain confirmed by molecular subtyping.

We report a case of recurrent listeriosis for which molecular subtyping by automated ribotyping and pulsed-field gel electrophoresis confirmed either relapse of infection or reinfection due to a common source almost 9 months after initial infection due to a unique Listeria monocytogenes strain in a patient with colorectal cancer. This case report illustrates the potential use of molecular subtyping to further understand the pathogenesis and epidemiology of listeriosis and the potential for relapse of Listeria infections in humans.

Aged↗
PubMed2001

Expression of the cell cycle phosphatase cdc25C is down-regulated by the tumor suppressor protein p53 but not by p73.

The cdc25C phosphatase dephosphorylates cdc2 kinase which then in complex with cyclin B can catalyse transition from the G(2) phase to mitosis. We demonstrate that transcription of cdc25C is repressed by p53 in a dose-dependent manner. In stably transfected DLD-1 colorectal adenocarcinoma cells, cdc25C expression is down-regulated when p53 is induced from a (tet)-off-regulated system. In contrast to p53, its homologue p73 is not able to down-modulate cdc25C expression. A previously identified site in the cdc25C promoter can bind p53 in vitro and, when placed in a heterologous construct, is able to activate transcription. However, transcriptional repression by p53 is not mediated through this site but is dependent on a segment containing three CCAAT-boxes. In general down-regulation of cdc25C transcription by reducing the levels of active cdc2 kinase contributes to G(2) arrest and G(2)/M checkpoint control. This reveals functional differences between p73 and p53 in regulating cell division.

Animals↗
PubMed2001

Inhibition of 15-lipoxygenase leads to delayed organelle degradation in the reticulocyte.

Mammalian cells are characterized by an endomembrane system. Nevertheless, some cells lose these membranes during their terminal differentiation, e.g. red blood cells and lens fiber cells of the eye. 15-Lipoxygenase is believed to be critical for this membrane degradation. Here we use cultivated rabbit reticulocytes in the presence or absence of a lipoxygenase inhibitor to provide further evidence for the importance of 15-lipoxygenase for the in vivo degradation of mitochondria. We find that inhibitor treatment retarded mitochondrial degradation, as shown by persistence of marker proteins and by direct visualization of mitochondria by electron microscopy.

Animals↗
PubMed2001

Characterization of the prfA virulence gene cluster insertion site in non-hemolytic Listeria spp.: probing the evolution of the Listeria virulence gene island.

The prfA virulence gene cluster is present between prs and ldh in the pathogenic L. monocytogenes and L. ivanovii, but absent from the non-pathogenic L. innocua and L. welshimeri. To probe the evolution of this virulence gene cluster, we sequenced the prs-ldh intergenic region in L. welshimeri and L. innocua. Two ORFs (ORFA and ORFB) were found in both species as well as in L. monocytogenes. Another ORF of unknown function (ORFZ) was found in L. monocytogenes and L. innocua, while two unique ORFs were present in L. welshimeri. ORFA and ORFB showed significant functional constraint, suggesting that further investigations in the functions of these genes, including possible roles in horizontal gene transfer or sequence deletion, are warranted. DNA sequences homologous to Tn1545 integration consensus sequences were found downstream of prs and ORFB, thus defining the likely junctions of the virulence gene island and indicating that the prs-ldh intergenic region may represent a Tn insertion hot spot. Our results are consistent with the hypothesis that a combination of horizontal gene transfer and deletion events mayhave been involved in the evolution of the prfA virulence gene cluster in Listeria.

Animals↗
PubMed2001

Molecular studies on the ecology of Listeria monocytogenes in the smoked fish processing industry.

We have applied molecular approaches, including PCR-based detection strategies and DNA fingerprinting methods, to study the ecology of Listeria monocytogenes in food processing environments. A total of 531 samples, including raw fish, fish during the cold-smoking process, finished product, and environmental samples, were collected from three smoked fish processing facilities during five visits to each facility. A total of 95 (17.9%) of the samples tested positive for L. monocytogenes using a commercial PCR system (BAX for Screening/Listeria monocytogenes), including 57 (27.7%) environmental samples (n = 206), 8 (7.8%) raw material samples (n = 102), 23 (18.1%) samples from fish in various stages of processing(n = 127), and 7 (7.3%) finished product samples (n = 96). L. monocytogenes was isolated from 85 samples (16.0%) using culture methods. Used in conjunction with a 48-h enrichment in Listeria Enrichment Broth, the PCR system had a sensitivity of 91.8% and a specificity of 96.2%. To track the origin and spread of L. monocytogenes, isolates were fingerprinted by automated ribotyping. Fifteen different ribotypes were identified among 85 isolates tested. Ribotyping data established possible contamination patterns, implicating raw materials and the processing environment as potential sources of finished product contamination. Analysis of the distribution of ribotypes revealed that each processing facility had a unique contamination pattern and that specific ribotypes persisted in the environments of two facilities over time (P < or = 0.0006). We conclude that application of molecular approaches can provide critical information on the ecology of different L. monocytogenes strains in food processing environments. This information can be used to develop practical recommendations for improved control of this important food-borne pathogen in the food industry.

Animals↗
PubMed2001

Characterization and pathogenic potential of Listeria monocytogenes isolates from the smoked fish industry.

This study was designed to evaluate the hypothesis that some of the Listeria monocytogenes subtypes associated with foods, specifically smoked fish, may have an attenuated ability to cause human disease. We tested this hypothesis by using two different approaches: (i) comparison of molecular subtypes found among 117 isolates from smoked fish, raw materials, fish in process, and processing environments with subtypes found among a collection of 275 human clinical isolates and (ii) the evaluation of the cytopathogenicity of industrial isolates. Ribotyping and PCR-restriction fragment length polymorphism typing of the hlyA and actA genes differentiated 23 subtypes among the industrial isolates and allowed classification of the isolates into three genetic lineages. A significantly higher proportion of human isolates (69.1%) than industrial isolates (36.8%) were classified as lineage I, which contains human sporadic isolates and all epidemic isolates. All other industrial isolates (63.2%) were classified as lineage II, which contains only human sporadic isolates. Lineage I ribotypes DUP-1038B and DUP-1042B represented a significantly higher proportion of the human isolates than industrial isolates (5.1%). Lineage II ribotypes DUP-1039C, DUP-1042C, and DUP-1045, shown previously to persist in the smoked fish processing environment, represented nearly 50% of the industrial isolates, compared to 7.6% of the human isolates. Representatives of each subtype were evaluated with a tissue culture plaque assay. Lineage I isolates formed plaques that were significantly larger than those formed by lineage II isolates. Isolates from the smoked fish industry representing three ribotypes formed no plaques or small plaques, indicating that they had an impaired ability to infect mammalian cells. While L. monocytogenes clonal groups linked to human listeriosis cases and outbreaks were isolated, our data also suggest that at least some L. monocytogenes subtypes present in ready-to-eat foods may have limited human-pathogenic potential.

Animals↗
PubMed2001

Correlations between molecular subtyping and serotyping of Listeria monocytogenes.

To define relationships between Listeria monocytogenes genetic lineages, ribotypes, and serotypes, 235 L. monocytogenes isolates were characterized by serotyping and automated EcoRI ribotyping. Genetic lineage predicted the following serovar clusters: lineage I, comprising serotypes 1/2b, 3b, 3c, and 4b; lineage II, comprising serotypes 1/2a, 1/2c, and 3a; and lineage III, comprising serotypes 4a and 4c. Some EcoRI ribotypes contained multiple serotypes; a subset of these isolates was further differentiated with PvuII ribotyping. Of the 12 resultant EcoRI-PvuII combination types, only 4 contained multiple serotypes, demonstrating the potential of ribotyping for serotype prediction.

Animals↗
PubMed2001

Automated ribotyping using different enzymes to improve discrimination of Listeria monocytogenes isolates, with a particular focus on serotype 4b strains.

To develop improved automated subtyping approaches for Listeria monocytogenes, we characterized the discriminatory power of different restriction enzymes for ribotyping. When 15 different restriction enzymes were used for automated ribotyping of 16 selected L. monocytogenes isolates, the restriction enzymes EcoRI, PvuII, and XhoI showed high discriminatory ability (Simpson's index of discrimination > 0.900) and produced complete and reproducible restriction cut patterns. These three enzymes were thus evaluated for their ability to differentiate among isolates representing the two major serotype 4b epidemic clones, those having ribotype reference pattern DUP-1038 (51 isolates) and those having pattern DUP-1042 (20 isolates). Among these isolates, PvuII provided the highest discrimination for a single enzyme (nine different subtypes; index of discrimination = 0.518). A combination of PvuII and XhoI showed the highest discriminatory ability (index of discrimination = 0.590) for these isolates. A group of 44 DUP-1038 isolates and a group of 12 DUP-1042 isolates were identical to each other even when the combined data for all three enzymes were used. We conclude that automated ribotyping using different enzymes allows improved discrimination of L. monocytogenes isolates, including epidemic serotype 4b strains. We furthermore confirm that most of the isolates representing the genotypes linked to the two major epidemic L. monocytogenes clonal groups form two genetically homogeneous groups.

Bacterial Typing Techniques↗
PubMed2001

Comparative evaluation of culture- and BAX polymerase chain reaction-based detection methods for Listeria spp. and Listeria monocytogenes in environmental and raw fish samples.

Two commercial polymerase chain reaction (PCR)-based Listeria detection systems, the BAX for Screening/Listeria monocytogenes and the BAX for Screening/Genus Listeria, and a culture-based detection system, the Biosynth L. monocytogenes Detection System (LMDS), were evaluated for their ability to detect L. monocytogenes and Listeria spp. in raw ingredients and the processing environment. For detection of L. monocytogenes from raw fish, enrichment was performed in Listeria enrichment broth (LEB), followed by plating on both Oxford agar and LMDS L. monocytogenes plating medium (LMPM). Detection of Listeria and L. monocytogenes from environmental samples was performed using LMDS enrichment medium, followed by plating on both Oxford agar and LMPM. A total of 512 environmental samples and 315 raw fish were taken from two smoked fish processing facilities and screened using these molecular and cultural Listeria detection methods. The BAX for Screening/L monocytogenes was used to screen raw fish and was 84.8% sensitive and 100% specific. The BAX for Screening/Genus Listeria was evaluated on environmental samples and had 94.7% sensitivity and 97.4% specificity. In conjunction with enrichment in LEB, LMPM had a sensitivity and specificity for detection of L. monocytogenes from raw fish of 97.8 and 100%, respectively. Use of LMDS enrichment medium followed by plating on LMPM allowed for sensitivity and specificity rates of 94.8 and 100%, respectively, for detection of L. monocytogenes from environmental samples. We conclude that both the BAX systems and the use of LMPM allow for reliable and rapid detection of Listeria spp. and L. monocytogenes. While the BAX systems provide screening results in about 3 days, the use of LMPM allows for L. monocytogenes isolation in 4 to 5 days.

Animals↗
PubMed2000

The alpha and beta subunit of the nascent polypeptide-associated complex have distinct functions.

Nascent polypeptide-associated complex (NAC) is probably the first cytosolic protein to contact nascent polypeptide chains emerging from ribosomes. In this way NAC prevents inappropriate interactions with other factors. Eventually other factors involved in targeting and folding, like the Signal Recognition Particle or cytosolic chaperones, must gain access to the nascent chain. All NAC preparations to date consist of two copurifying polypeptides. Here we rigorously show that these two polypeptides, termed alpha- and betaNAC, form a very stable complex in vivo and in vitro and that a functional complex can be reconstituted from the individual subunits. A dissection of the contributions of the individual subunits to NACs function revealed that both subunits are in direct contact with nascent polypeptide chains on the ribosome and that both contribute to the prevention of inappropriate interactions. However, betaNAC alone directly binds to the ribosome and is sufficient to prevent ribosome binding to the endoplasmic reticulum membrane.

Amino Acid Sequence↗
PubMed2000

In vitro binding of ribosomes to the beta subunit of the Sec61p protein translocation complex.

The Sec61p complex forms the core element of the protein translocation complex (translocon) in the rough endoplasmic reticulum (rough ER) membrane. Translating or nontranslating ribosomes bind with high affinity to ER membranes that have been stripped of ribosomes or to liposomes containing purified Sec61p. Here we present evidence that the beta subunit of the complex (Sec61beta) makes contact with nontranslating ribosomes. A fusion protein containing the Sec61beta cytoplasmic domain (Sec61beta(c)) prevents the binding of ribosomes to stripped ER-derived membranes and also binds to ribosomes directly with an affinity close to the affinity of ribosomes for stripped ER-derived membranes. The ribosome binding activity of Sec61beta(c), like that of native ER membranes, is sensitive to high salt concentrations and is not based on an unspecific charge-dependent interaction of the relatively basic Sec61beta(c) domain with ribosomal RNA. Like stripped ER membranes, the Sec61beta(c) sequence binds to large ribosomal subunits in preference over small subunits. Previous studies have shown that Sec61beta is inessential for ribosome binding and protein translocation, but translocation is impaired by the absence of Sec61beta, and it has been proposed that Sec61beta assists in the insertion of nascent proteins into the translocation pore. Our results suggest a physical interaction of the ribosome itself with Sec61beta; this may normally occur alongside interactions between the ribosome and other elements of Sec61p, or it may represent one stage in a temporal sequence of binding.

Animals↗
PubMed2000

YidC mediates membrane protein insertion in bacteria.

The basic machinery for the translocation of proteins into or across membranes is remarkably conserved from Escherichia coli to humans. In eukaryotes, proteins are inserted into the endoplasmic reticulum using the signal recognition particle (SRP) and the SRP receptor, as well as the integral membrane Sec61 trimeric complex (composed of alpha, beta and gamma subunits). In bacteria, most proteins are inserted by a related pathway that includes the SRP homologue Ffh, the SRP receptor FtsY, and the SecYEG trimeric complex, where Y and E are related to the Sec61 alpha and gamma subunits, respectively. Proteins in bacteria that exhibit no dependence on the Sec translocase were previously thought to insert into the membrane directly without the aid of a protein machinery. Here we show that membrane insertion of two Sec-independent proteins requires YidC. YidC is essential for E. coli viability and homologues are present in mitochondria and chloroplasts. Depletion of YidC also interferes with insertion of Sec-dependent membrane proteins, but it has only a minor effect on the export of secretory proteins. These results provide evidence for an additional component of the translocation machinery that is specialized for the integration of membrane proteins.

ATP-Binding Cassette Transporters↗